,,transcrib]',s ,,note3 ,9 transcrib+ ?is book1 ! pro(read]s f\nd & correct$ sev]al m9or typographical errors :i* did n affect ! s5se ( ! text4 ,9 ! caption to ,figure #eda1 ! equation = ! voltage ( a ,we/on cell at diff]5t temp]atures 0 miss+ a digit #a & ?is has be5 correct$4 ,!re is a ref]5ce to a ,figure #fai b no su* figure exi/s 9 ! orig9al text4 ,!re are ref]5ces to a ,figure #aai & a ,figure #ddc2 ^! presumably exi/ 9 "o ( ! prec$+ volumes ( ! s]ies4 ,?r\gh\t1 ! use ( italic type is indicat$ by und]scores4 ,9 equations1 sup]scripts are indicat$ by a c>et & braces1 z 9 ,x#b = ,x squ>$4 ,subscripts are indicat$ by und]score & braces1 z 9 ,et to mean ,e sub t4 ,,! ,,?\ght ,,is ,,9 ,,! ,,"q ,,! ,,in=mation ,,is ,,9 ,,! ,,answ] ,,hawk9s ,,electrical ,,guide ,,numb] ,,?ree ,,que/ions ,,answ]s ,,illu/rations ,a ,,progressive ,,c\rse ,,( ,,/udy ,,= ,,eng9e]s1 ,,electricians1 ,,/ud5ts ,,& ,,^? ,,desir+ ,,to ,,acquire ,a ,,work+ ,,k ,,( ,,electricity ,,& ,,its ,,applications ,a ,,practical ,,treatise by ,,hawk9s ,,& ,,/aff ,,!o4 ,,audel ,,co4 #gb ,,fif? ,,ave4 ,,new ,,york ,,copyright$1 #aiad1 by ,,!o4 ,,audel ,,co41 ,new ,york4 ,pr9t$ 9 ! ,unit$ ,/ates4 ,,table ,,( ,,cont5ts ,,guide ,,no4 #c4 ,,galvanomet]s #dca to #dfd ,action ( compass ne$le--simple galvanomet]--diff]5ce betwe5 galvanoscope & galvanomet]--s5sibility--action ( %ort & long coil galvanomet]s--classes ( galvanomet]--a/atic galvanomet]--tang5t galvanomet]--graduation ( tang5t galvanomet] scale--table ( galvanomet] con/ants--me*anical explanation ( tang5t law--s9e galvanomet]--table ( natural s9es & tang5ts--comp>ison ( s9e & tang5t galvanomet]s--diff]5tial galvanomet]--balli/ic galvanomet]--kick--damp+ effect--use ( mirrors 9 galvanomet]s--lamp & scale--damp+--,d',arsonval galvanomet]3 con/ruction1 op]ation2 uses--galvanomet] con/ant or figure ( m]it--%unts4 ,,te/+ ,,& ,,te/+ ,,app>atus #dfe to #ecf ,pressure measurem5t--,cl>k cell--,we/on cadmium cell--pressure measurem5t error ) ord9>y voltmet]--,int]national volt--hydraulic analogy ( amp]es--c\lombs--curr5t measurem5t--,int]national amp]e--voltamet]s--,ohm's law & ! ohm--,int]national ohm--ohm table--practical /&>ds ( resi/ance--v>i\s me?ods ( resi/ance measurem5t--direct deflection me?od--me?od ( sub/itution--resi/ance box--fall ( pot5tial me?od--diff]5tial galvanomet] me?od--drop me?od--voltmet] me?od--,:eat/one bridge--usual arrangem5t ( resi/ances ( ,:eat/one bridge--ratio coils ( ,:eat/one bridge--! decade plan--two plug arrangem5t--plug out & plug 9 type ( resi/ance box--te/+ sets--direct deflection me?od ) ,que5 ,acme set--ohmmet]--fall ( pot5tial me?od ) ,que5 ,acme set--app>atus = measur+ l[ resi/ances--h[ to *eck a voltmet]--,kelv9 wire bridge--int]nal resi/ance measurem5t--,ev]%$ portable ohmmet] set--,l & ,n fault f9d]--ammet] te/--diagram ( ,que5 /&>d pot5tiomet]--diagrams illu/rat+ loop te/+--! ,murray loop--! ,v>ley loop--special loop--! pot5tiomet]--location ( op5s--to pick out faulty wires 9 a cable--voltage ( cell measurem5t ) pot5tiomet]--c>e ( pot5tiomet]--location ( faults :]e ! loop is compos$ ( cables ( diff]5t cross sections4 ,,ammet]s1 ,,voltmet]s1 ,,& ,,wattmet]s #ecg to #egb ,def9ition ( ammet]--classification ( ammet] & voltmet]s--mov+ iron type in/rum5t--,key/one voltmet]--w9d+ 9 ammet]s & volts--connections = s]ies & %unt ammet]s--voltmet] connections--,we/+h\se ammet] %unts--v>i\s types ( in/rum5t--plung] type in/rum5t--magnetic vane in/rum5t--incl9$ coil in/rum5t--,:itney hot wire in/rum5ts--pr9ciple ( electro/atic in/rum5ts--multipli]s--portable %unts--,siem5s electro-dynamomet]--/ation in/rum5ts--,?ompson watt h\r met]--h[ to read a met]--in/allation ( wattmet]s--,we/+h\se watt h\r met]--,?ompson prepaym5t watt h\r met]--h[ to te/ a met]--,sangamo watt h\r met]--,columbia watt h\r met]--,duncan watt h\r met]4 ,,op]ation ,,( ,,dynamos #egc to #eif ,be=e />t+ a dynamo--adju/+ ! bru%es--bru% position--h[ to set ! bru%es--me?od ( sold]+ cable to c>bon bru%--bru% contact pressure--direction ( rotation--me?od ( w9d+ cables ) m>l9--me?od ( assembl+ core discs--/>t+ a dynamo--t9n+ block = electric sold]+ tool--%unt dynamos 9 p>allel--%unt dynamos on ?ree wire sy/em--h[ to />t a s]ies ma*9e--! t]m build up--h[ to />t a %unt or comp\nd ma*9e--pick+ up--indication ( rev]s$ connections--h[ to correct rev]s$ pol>ity--f9d+ ! rev]s$ coil--loss ( residual magnetism--rem$y = rev]s$ dynamo--att5tion :ile runn+--lead ( bru%es--me?od ( tak+ temp]ature--lubrication--oils--all[able degree ( heat+--att5tion to bru%es & bru% ge>4 ,,c\pl+ ,,( ,,dynamos #eig to #faj ,s]ies & p>allel connections--c\pl+ s]ies dynamos 9 s]ies2 9 p>allel--equaliz]--%unt dynamos 9 s]ies2 9 p>allel--swit*+ dynamo into & out ( p>allel--to cut out a ma*9e--divid+ ! lead--comp\nd dynamos 9 s]ies2 9 p>allel--equaliz] connection--swit*+ a comp\nd dynamo into & out ( p>allel--equaliz+ ! load--%unt & comp\nd dynamos 9 p>allel4 ,,dynamo ,,fails ,,to ,,excite #faa to #fbb ,v>i\s causes--bru%es n prop]ly adju/$--defective contacts--incorrect adju/m5t ( regulators--spe$ too l[--te/+ = break--insuffici5t residual magnetism2 rem$y--op5 circuits--te/ = field circuit break]s--probable location ( breaks--,watson armature discs--,=t ,wayne commutator tru+ device--%ort circuits--,watson armature--wrong connections--rev]s$ field magnetism4 ,,armature ,,tr\bles #fbc to #fcd ,causes--h[ avoid$--v>i\s faults--%ort circuit 9 individual coils--location ( faulty coil--te/ = break 9 armature lead--b> to b> te/ = op5 or %ort circuit 9 coil or betwe5 segm5ts--%ort circuits betwe5 adjac5t coils--alt]nate b> te/ = %ort circuits betwe5 sections--%ort circuits betwe5 sections ?r\gh frame or core ( armature2 betwe5 sections ?r\gh b9d+ wires--p>tial %ort circuits 9 armatures--me?od ( te/+ = breaks--burn+ ( armature coils--,watson field coils--gr\nds 9 armatures--me?od ( locat+ gr\nd$ armature coil--magneto te/ = gr\nd$ armatures--me?od ( b9d+ armature w9d+--breaks 9 armature circuit4 ,,c>e ,,( ,,! ,,commutator ,,& ,,bru%es #fce to #feb ,conditions = satisfactory op]ation--oil = commutator--att5tion to bru%es--,bissell bru% ge>--two k9ds ( sp>k+--commutator clamp--causes ( sp>k+--bad adju/m5t ( bru%es--rock+--bad condition ( bru%es--bru%es mak+ bad contact--bad condition ( commutator--detection ( untrue commutator--high segm5ts--flats--causes ( flats2 rem$y--me?od ( repair+ brok5 jo9t betwe5 commutator segm5t & lug--segm5ts loose or knock$ 9--h[ to re-turn a commutator--,bissell commutators--ov]load ( dynamo--me?od ( repair+ l>ge hole burn$ 9 two adjac5t b>s ( a commutator--op]at+ dynamos ) metal bru%es--indication ( excessive voltage--me?od ( smoo?+ commutator ) a /one--causes ( excessive voltage--loose connections1 t]m9als1 etc41--breaks 9 armature circuit--s&pap] hold] = commutator--%ort circuits1 9 armature circuits2 9 field--breaks 9 field--s&pap] block--%ort circuits 9 commutator4 ,,heat+ #fec to #ffb ,v>i\s causes--h[ detect$--proc$ure--heat+1 ( connections2 ( bru%es1 commutator & armature--excessive heat+--v5tilat$ commutator--self-oil+ be>+--"s causes ( hot be>+--effect ( hot be>+s--po9ts relat+ to hot be>+s--op]ation above rat$ voltage & bel[ normal spe$--=c$ sy/em ( lubrication--heat+ ( field magnets--causes ( eddy curr5ts 9 pole pieces--detection ( moi/ure 9 field coils--indication ( %ort circuits 9 field coils4 ,,op]ation ,,( ,,motors #ffc to #fif ,be=e />t+ a motor--/>t+ a motor--v>i\s />t+ resi/ances--/>t+ boxes--spe$ regulators--,cutl] ,hamm] />t]--"t requir$ to />t motor--h[ to />t--slid+ contact />t]s--s]ies motors on batt]y circuits--/>t+ a %unt motor--multiple swit* />t]s--effect ( rev]se voltage--rheo/at ) no voltage & ov]load release--failure to />t--/>t+ panel--,cutl] ,hamm] />t+ rheo/ats--,all5 ,bradley automatic />t]--,monitor />t] ) relay = pu% button control--a remote control ( %unt motors--regulation ( motor spe$2 v>i\s me?ods--,monitor pr9t+ press controll]--spe$ regulation ( s]ies motor1 by %ort circuit+ sections ( ! field w9d+--v>y+ ! spe$ ( %unt & comp\nd motors--,cutl] ,hamm] multiple swit* />t]--regulation by armature resi/ance--,comp\nd />t]--regulation by %unt field resi/ance--,holz] ,cabot in/ructions = %unt w\nd motor--,reliance adju/able spe$ motor--,cutl] ,hamm] rev]sible />t]--comb9$ armature & %unt field control--selection ( />t]s & regulators--,watson commutators--organ bl[] spe$ regulator--,g5]al ,electric controll]--spe$ regulation ( traction motors--controll] ( ! ,rau* & ,lang electric vehicles--two motor regulation--controll] connection diagrams--/opp+ a motor4 ,,*apt] ,,xxvi ,,galvanomet]s ,if a compass ne$le be all[$ to come to re/ 9 its natural position1 & a curr5t ( electricity be pass$ ?r\gh a wire j ov] x f nor? to s\?1 ! nor? seek+ end ( ! ne$le w be deflect$ t[>d ! ea/4 ,if ! wire be plac$ "u ! ne$le & ! curr5t cont9u$ f nor? to s\? ! ne$le w be deflect$ t[>d ! we/4 ,aga91 if ! curr5t be pass$ f nor? to s\? ov] ! ne$le1 & back f s\? to nor? "u ! ne$le1 z %[n 9 fig4 #ejd1 ! magnetic effect w be d\bl$1 & ! ne$le deflect$ proportionately4 ,^u ^! ph5om5a dep5d ! work+ ( galvanomet]s4 ,illu/ration3 ,fig4 #ejc4--;,effect ( neighbor+ curr5t ^u a magnetic ne$le4 ,above ! ne$le & p>allel to x is a conductor c>ry+ an electric curr5t1 ! curr5t fl[+ 9 ! direction indicat$ by ! arr[4 ,?is causes ! nor? pole ( ! ne$le to turn t[>d ! ea/4 ,if ! conductor be held bel[ ! ne$le1 its nor? pole w turn 9 ! opposite direction or t[>d ! we/4 ,^! movem5ts are easily det]m9$ by ,amp]e's rule z foll[s3 ,if a man c\ld swim 9 ! conductor ) ! curr5t1 & turn to face ! ne$le1 !n ! nor? pole ( ! ne$le w be deflect$ t[>d 8 left h&4 ,ques4 ,describe a simple galvanomet]4 ,ans4 ,x consi/s ess5tially ( a magnetic ne$le susp5d$ )9 a coil ( wire1 & free to sw+ ov] ! face ( a graduat$ dial4 ,ques4 ,:at is a galvanoscope & h[ does x diff] f a galvanomet]8 ,ans4 ,a galvanoscope1 z %[n 9 fig4 #ejd1 s]ves m]ely to indicate ! pres5ce ( an electric curr5t )\t measur+ its /r5g?4 ,x is an indicator ( curr5ts :]e ! movem5t ( ! ne$le %[s ! direction ( ! curr5t1 & indicates :e!r x is a /rong or a weak "o4 ,:5 ! value ( ! read+s has be5 det]m9$ by exp]im5t or calculation any galvanoscope becomes a galvanomet]4 ,illu/ration3 ,fig4 #ejd4--;,effect ^u a magnetic ne$le ( a neighbor+ curr5t 9 a loop4 ,9 ?is arrangem5t ! same conductor is simply c>ri$ back b5ea? ! ne$le & h5ce bo? ! upp] & l[] portions t5d to turn x 9 ! same direction1 :ile ! side bran* or v]tical section is ineffective4 ,9 accordance ) ,amp]e's swimm+ rule1 ! upp] wire causes ! ,n pole ( ! ne$le to turn to ! left1 :ile if a man c imag9e himself swimm+ 9 ! l[] wire 9 ! direction ( ! curr5t1 & fac+ ! ne$le 7t is1 swimm+ on 8 back71 ! ,n pole ( ! ne$le w turn to 8 left--t is to ! ea/4 ,! effect ( ! loop !n has d\ble ! effect ( ! s+le wire 9 fig4 #ejc4 ,ques4 ,= :at use are galvanomet]s employ$8 ,ans4 ,!y are us$ = detect+ ! pres5ce ( an electric curr5t1 & = det]m9+ its direction & /r5g?4 ,ques4 ,h[ is ! direction & /r5g? ( ! curr5t indicat$8 ,ans4 ,:5 a galvanomet] is connect$ 9 a circuit1 ! direction ( ! curr5t is indicat$ by ! side t[>ds :i* ! nor? pole ( ! ne$le moves1 & ! curr5t /r5g? by ! ext5t ( ! ne$le's deflection4 ,illu/ration3 ,fig4 #eje4--;,effect ^u a magnetic ne$le ( a neighbor+ curr5t 9 a coil4 ,! coil z %[n1 is equival5t to sev]al loops1 t is1 ! =ce t5d+ to deflect ! ne$le is equal to t ( a s+le loop multipli$ by ! numb] ( turns4 ,h5ce1 by us+ a coil ) a l>ge numb] ( turns1 a galvanomet] may be made v s5sitive s t ! ne$le w be p]ceptibly deflect$ by v feeble curr5ts4 ,an in/rum5t1 z %[n 9 ! figure is call$ a galvanoscope4 ,:5 x is accurately con/ruct$1 & suppli$ ) a scale %[+ h[ _m degrees ! ne$le is deflect$ x is !n call$ a galvanomet]4 ,ques4 ,h[ %\ld a galvanomet] be set up be=e us+8 ,ans4 ,:5 no curr5t is fl[+1 ! coil %\ld be p>allel to ! magnetic ne$le :5 at re/4 ,ques4 ,:at is a s5sitive galvanomet]8 ,ans4 ,"o :i* requires a v small curr5t or pressure to produce a /at$ deflection4 ,x does n foll[ t a galvanomet] :i* is s5sitive = curr5t measurem5t w also be s5sitive = pressure measurem5t4 ,illu/ration3 ,fig4 #ejf4--;,bunnell simple detector galvanomet]4 ,x has middle clamps & scale divid$ into degrees4 ,ques4 ,def9e ! t]m s5sibility4 ,ans4 ,) ref]5ce to mirror reflect+ galvanomet]s x may be def9$ 9 ?ree ways4 ,fir/1 9 megohms1 ! s5sibility be+ ! numb] ( megohms ?r\gh :i* "o volt w produce a deflection ( "o millimet] ) ! scale at "o met] di/ance4 ,second1 9 micro-volts1 ! s5sibility be+ ! numb] ( micro-volts :i* appli$ directly to ! t]m9als ( ! galvanomet] w produce a deflection ( "o millimet] on a scale "o met] f mirror4 ,! s5sibility is be/ /at$ 9 megohms = high resi/ance galvanomet]s & 9 micro-volts = l[ resi/ance galvanomet]s1 & is frequ5tly giv5 bo? = galvanomet]s = int]m$iate resi/ance4 ,?ird1 9 micro-amp]es1 ! s5sibility be+ ! numb] ( micro-amp]es t w give "o millimet] deflection ) scale at a di/ance ( "o met]4 ,ques4 ,^u :at does ! s5sibility dep5d8 ,ans4 #a1 ,^u ! numb] ( times ! curr5t circulates ar\nd ! coil1 #b1 ! di/ance ( ! ne$le f ! coil1 #c1 ! weight ( ! ne$le1 #d1 ! curr5t /r5g?1 & #e1 ! am\nt ( friction produc$ by its movem5t4 ,illu/ration3 ,fig4 #ejg4--;,breguet upright galvanomet] ) glass %ade4 ,illu/ration3 ,fig4 #ejh4--;,bunnell horizontal galvanomet]4 ,x has two coils1 "o ( :i* is ( z]o resi/ance & "o ( fifty ohms resi/ance adapt+ x to a v>iety ( te/4 ,! ne$le is usually q small1 & (t5 a comp\nd "o4 ,9 v s5sitive galvanomet]s1 ! coils are w\nd ) ?\s&s ( turns ( v f9e wire1 & %unts are g5]ally us$ 9 connection ) !m4 ,,note4--,/rong curr5ts mu/ n be pass$ ?r\gh v s5sitive galvanomet]s1 = ev5 if !y be n ru9$1 ! deflections ( ! ne$le w be too l>ge to give accurate measurem5ts4 ,9 su* cases ! galvanomet] is us$ ) a %unt1 or coil ( wire arrang$ s t ! great] "p ( ! curr5t w fl[ ?r\gh x1 & only a small portion ?r\gh ! galvanomet]4 ,ques4 ,:at two k9ds ( coil are us$8 ,ans4 ,! %ort coil & ! long coil4 ,ques4 ,:at is ! diff]5ce betwe5 a %ort coil & a long coil galvanomet]8 ,ans4 ,a %ort coil galvanomet] has a coil consi/+ ( a few turns ( heavy wire2 a long coil galvanomet] is w\nd ) a l>ge numb] ( turns ( f9e wire4 ,illu/ration3 ,fig4 #eji4--;,bunnell galvanomet] = measurem5ts ( in/rum5ts1 l9es1 batt]ies1 wires & any object f #a_/ajj to #aj1jjj ohms or m4 ,ques4 ,:at is ! action ( %ort & long coil galvanomet]s8 ,ans4 ,) a giv5 curr5t1 ! total magnetiz+ =ce :i* deflects ! ne$le is ! same1 b ) a %ort coil1 x is produc$ by a l>ge curr5t circulat+ ar\nd a few turns1 in/ead ( a small curr5t circulat+ ar\nd ?\s&s ( turns z 9 ! long coil4 ,! %ort coil be+ ( l[ resi/ance is us$ to measure ! curr5t1 & ! long coil ) high resi/ance1 is suitable = measur+ ! pressure4 ,h5ce1 a %ort coil in/rum5t ) its scale directly graduat$ 9 amp]es is an ammet]1 & ! long coil type ) graduation 9 volts is a voltmet]4 ,classes ( ,galvanomet]4--,!re are num]\s k9ds ( galvanomet] design$ to meet ! v>i$ requirem5ts4 ,accord+ to con/ruction1 galvanomet]s may be divid$ into two classes1 z ^? hav+3 #a4 ,movable magnet & /ation>y coil2 #b4 ,/ation>y magnet & movable coil4 ,illu/ration3 ,fig4 #eaj4--;,a/atic ne$les4 ,two magnetic ne$les ( equal mom5t are m\nt$ 9 opposition on a light support4 ,! :ole sy/em is susp5d$ by a delicate fibre1 & :5 plac$ 9 a uni=m magnetic field su* z t ( ! e>?1 !re w be no t5d5cy to assume any fix$ direction1 ! only re/ra9+ influ5ce on ! ne$les be+ t due to torsion 9 ! susp5sion fibre4 ,ei!r type may be con/ruct$ ) %ort or long coil1 & !re are sev]al ways 9 :i* ! deflections are indicat$4 ,! pr9cipal =ms ( galvanomet] are z foll[s3 #a4 ,a/atic2 #b4 ,tang5t2 #c4 ,s9e2 #d4 ,diff]5tial2 #e4 ,balli/ic2 #f4 ,d',arsonval4 ,a/atic ,galvanomet]4--,x has be5 po9t$ out h[ a compass ne$le is affect$ :5 a wire c>ry+ a curr5t is held ov] or "u x1 ! ne$le be+ turn$ 9 "o direction 9 ! fir/ in/ance1 & 9 ! opposite direction = ! second position ( ! wire4 ,illu/ration3 ,fig4 #eaa4--;,connections ( s+le coil a/atic ne$les4 ,! coil surr\nds ! l[] ne$le & ! direction ( ! curr5t betwe5 ! two ne$les t5ds to turn !m ! same way4 ,! e>?'s magnetism naturally holds ! compass ne$le nor? & s\?4 ,! magnetic field encircl+ ! wire1 be+ at "r angles to ! ne$le 7:5 ! wire itself is p>allel !re)71 op]ates to turn x f its normal position1 nor? & s\?1 s z to set x p>tially ea/ & we/4 ,h[ev]1 on acc\nt ( ! fact t ! e>?'s magnetism does ex]t "s =ce t5d+ to hold ! ne$le nor? & s\?1 x is evid5t t no matt] h[ /rong ! curr5t1 ! latt] c nev] succe$ 9 turn+ ! ne$le entirely ea/ & we/4 ,! accompli%m5t ( ?is is fur!r prev5t$ by ! reason ( ! po9ts ( ! ne$le1 :]e ! magnetic effect is greate/1 quickly pass+ out ( ! rea* ( ! magnetic field1 :]e x is n[ practically op]at$ on only 9 a slight degree4 ,?us x w\ld take q a p[]ful curr5t to hold ! ne$le deflect$ any appreciable di/ance4 ,! use ( a %ort] ne$le is1 !re=e1 m desirable4 ,x is evid5t 9 ?is /yle ( in/rum5t t ! effect ( ! curr5t _c be accurately measur$1 because x acts 9 opposition to ! e>?'s magnetism1 & z ?is is con/antly v>y+1 "s me?od mu/ be employ$ :i* w ei!r de/roy ! e>?'s magnetism or else neutralize x4 ,9 ! a/atic galvanomet]1 ! e>?'s magnetism is neutraliz$ by means ( a/atic ne$les4 ,^! consi/ ( a comb9ation ( two magnetic ne$les ( equal size & /r5g?1 connect$ rigidly toge!r ) _! poles po9t+ 9 opposite & p>allel directions1 z %[n 9 fig4 #eaj4 ,z ! nor? pole ( ! e>? attracts ! s\? pole ( "o ( ! ne$les1 x repels ) equal /r5g? ! nor? pole ( ! o!r ne$le1 h5ce1 ! comb9ation is indep5d5t ( ! e>?'s magnetism & w rema9 at re/ 9 any position4 ,illu/ration3 ,fig4 #eab4--;,connections ( d\ble coil a/atic ne$les4 ,) ?is arrangem5t1 ! direction ( curr5t 9 bo? coils w t5d to turn ! sy/em 9 ! same direction1 mak+ ! ne$les m s5sitive ?an ) a s+le coil z 9 fig4 #eaa4 ,if "o ( ! ne$les be surr\nd$ by a coil1 z %[n 9 fig4 #eaa1 ! magnetic effect ( ! curr5t w be correctly indicat$ by ! deflection ( ! ne$le4 ,sometimes ea* ne$le is surr\nd$ by a coil1 z 9 fig4 #eab1 ! coils be+ s connect$ t ! direction ( curr5t 9 ea* w t5d to deflect ! ne$les 9 ! same direction4 ,ques4 ,= :at use is ! a/atic galvanomet] adapt$8 ,ans4 ,= ! detection ( small curr5ts4 ,x is us$ 9 ! nil or z]o me?ods1 9 :i* ! curr5t betwe5 ! po9ts to :i* ! galvanomet] is connect$ is r$uc$ to z]o4 ,illu/ration3 ,fig4 #eac4--,que5 reflect+ a/atic galvanomet]4 ,x is m\nt$ on a mahogany base ) levell+ screws4 ,a pla9 mirror is atta*$ above ! upp] ne$le4 ,! entire comb9ation ( mirror & ne$les is susp5d$ by unspun silk f ! int]ior ( a brass tube1 :i* also c>ries a weak controll+ magnet4 ,a dial #d in*es 9 diamet] & graduat$ 9 degrees1 enables ! deflections ( ! ne$le to be accurately read4 ,! mirror c be us$ ) a read+ telescope & scale1 or by means ( a lant]n1 ! image ( a slit may be reflect$ f ! mirror to a scre54 ,resi/ance1 4#e to #a1jjj ohms4 ,ques4 ,^u :at does ! movem5t ( ! ne$les dep5d8 ,ans4 ,^u ! comb9$ effect ( ! magnetic attraction ( ! curr5t :i* t5ds to deflect ! ne$les1 & ! torsion 9 ! susp5sion fibre :i* t5ds to keep ! ne$le at ! z]o position4 ,ques4 ,does ! a/atic galvanomet] give correct read+s = diff]5t values ( ! curr5t8 ,ans4 ,:5 ! deflections are small 7t is1 less ?an #aj or #ae71 !y are v ne>ly proportional to ! /r5g? ( ! curr5ts t produce !m4 ,?us1 if a curr5t produce a deflection ( #f x is kn[n to be approximately ?ree times z /rong z a curr5t :i* only turns ! ne$le ?r\gh #b4 ,b ?is approximate proportion ceases to be true if ! deflection be m ?an #ae or #bj4 ,illu/ration3 ,fig4 #ead4--;,c5tral ,sci5tific ,co4 tang5t galvanomet]4 ,a #i in* brass r+ is m\nt$ on a mahogany base :i* rotates on a tripod provid$ ) levell+ screws4 ,! ne$le has an alum9um po9t] & jewell$ be>+4 ,! w9d+ consi/s ( #cjj turns ( magnet wire s connect$ to ! plugs 9 front t #bj1 #dj1 #hj1 or #afj turns or any comb9ation ( ^! numb]s may be us$4 ,= heavy curr5ts a b& ( copp] is us$ by connect+ to ! extra pair ( b9d+ po/s 9 ! re> ( ! in/rum5t4 ,ques4 ,:y does ! in/rum5t n give accurate read+s = l>ge deflections8 ,ans4 ,! ne$les are n s advantage\sly act$ ^u by ! curr5t1 s9ce ! poles are no long] )9 ! coils1 b protrude at ! side4 ,moreov]1 ! ne$les be+ oblique to ! =ce act+ on !m1 "p only ( ! =ce is turn+ !m aga9/ ! directive =ce ( ! fibre2 ! o!r "p is uselessly pull+ or pu%+ !m along _! l5g?4 ,illu/ration3 ,fig4 #eae4--;,bunnell tang5t galvanomet]4 ,?is in/rum5t is m\nt$ on a circul> h>d rubb] base1 #g-c_/h in*es diamet]1 provid$ ) levell+ screws & an*or+ po9ts4 ,! galvanomet] consi/s ( a magnetiz$ ne$le #g_/h in* 9 l5g?1 susp5d$ at ! c5t] ( a rubb] r+ six in*es 9 diamet]1 conta9+ ! coils4 ,!re are five coils ( #j1 #a1 #aj1 #ej & #aej ohms resi/ance4 ,! fir/ is a /\t copp] b& ( inappreciable resi/ance2 ! o!rs are ( diff]5t siz$ copp] wires1 c>efully insulat$4 ,five t]m9als are provid$1 m>k$1 respectively1 #j1 #a1 #aj1 #ej & #aej4 ,! ends ( ! coils are s arrang$ t ! plug ins]t$ at ! t]m9al m>k$ #ej puts 9 circuit all ! coils2 m>k$ at ! t]m9al #ej--;all except ! #aej ohm coil2 & s on1 till at ! z]o t]m9al only ! copp] b& is 9 circuit4 ,fix$ to ! ne$le1 :i* is balanc$ on jewel & po9t1 is an alum9um po9t] at "r angles1 ext5d+ across a five in* dial imm$iately b5ea?4 ,"o side ( ! dial is divid$ into degrees2 on ! o!r side1 ! graduations correspond to ! tang5t ( ! angles ( deflection4 ,ques4 ,h[ may correct read+s be obta9$8 ,ans4 ,! in/rum5t may be calibrat$1 t is1 x may be asc]ta9$ by special measurem5ts1 or by comp>ison ) a /&>d in/rum5t1 ! am\nts ( deflection correspond+ to p>ticul> curr5t /r5g?s4 ,?us1 if x be once kn[n t a deflection ( #cb on a p>ticul> galvanomet] is produc$ by a curr5t ( #a_/ajj ( an amp]e1 !n a curr5t ( t /r5g? w always produce on t in/rum5t ! same deflection1 unless f any accid5t ! torsion =ce or ! int5sity ( ! magnetic field be alt]$4 ,illu/ration3 ,fig4 #eaf4--,tang5t galvanomet]4 ,x consi/s ( a %ort magnetic ne$le susp5d$ at ! c5t] ( a coil ( l>ge diamet] & small cross section4 ,9 practice1 ! diamet] ( ! coil is ab\t #ag times ! l5g? ( ! ne$le4 ,if ! in/rum5t be s plac$ t1 :5 !re is no curr5t 9 ! coil1 ! susp5d$ magnet lies 9 ! plane ( ! coil1 t is1 if ! plane ( ! coil be set 9 ! magnetic m]idian1 !n ! curr5t pass+ ?r\gh ! coil is proportional to ! tang5t ( ! angle by :i* ! magnet is deflect$ f ! plane ( ! coil1 or z]o position--h5ce ! "n3 tang5t galvanomet]4 ,! ,tang5t ,galvanomet]4--,x is n possible to con/ruct a galvanomet] 9 :i* ! angle 7z measur$ 9 degrees ( arc7 ?r\gh :i* ! ne$le is deflect$ is proportional ?r\gh\t its :ole range to ! /r5g? ( ! curr5t4 ,b x is possible to con/ruct a v simple galvanomet] 9 :i* ! tang5t ( ! angle ( deflection %all be accurately proportional to ! /r5g? ( ! curr5t4 ,illu/ration3 ,fig4 #eag4--;,horizontal section ?r\gh middle ( tang5t galvanomet]1 %[+ magnetic :irls ar\nd ! coil & correspond+ deflection ( ne$le4 ,illu/ration3 ,fig4 #eah4--;,diagram ( =ces act+ on ! ne$le ( a tang5t galvanomet]4 ,a simple =m ( tang5t galvanomet] is %[n 9 fig4 #eaf4 ,! coil ( ?is in/rum5t consi/s ( a simple circle ( /\t copp] wire f t5 to fifte5 in*es 9 diamet]4 ,at ! c5t] is delicately susp5d$ a magnetiz$ /eel ne$le n exce$+ "o in* 9 l5g?1 & usually furni%$ ) a light index ( alum9um4 ,:5 ! galvanomet] is 9 use1 ! plane ( ! r+ mu/ be v]tical & 9 ! magnetic m]idian4 ,a horizontal section ?r\gh ! middle ( ! in/rum5t is %[n 9 fig4 #eag4 ,= simplicity1 ! coil is suppos$ to h b a s+le turn ( wire1 ! circles surr\nd+ ! wire repres5t+ ! magnetic l9es ( =ce4 ,by ext5d+ ! l9es ( =ce until !y rea* ! ne$le1 x w be se5 t ) a %ort ne$le1 ! deflect+ =ce acts 9 an ea/ & we/ direction :5 ! galvanomet] is plac$ ) its coil 9 ! magnetic m]idian4 ,if1 9 fig4 #eah1 ab repres5t ! deflect+ =ce act+ on ! ,n end ( ! ne$le1 ! compon5t ( ?is =ce t acts at a "r angle to ! ne$le w be ab cos x 9 :i*1 x is ! angle ( ! deflection4 ,! controll+ =ce is ad ,h & :5 ! ne$le is 9 equilibrium1 ! compon5t ae ,h s9 x is equal & opposite to ac1 h5ce ab cos x ,h s9 x f :i* ab ,h7s9 x _/ cos x7 ,h tan x ,s9ce ab is proportional to ! curr5t1 ab k ,c ,h tan x 9 :i* k is a con/ant dep5d+ ^u ! in/rum5t4 ,= any o!r curr5t ,c'1 k ,c' ,h tan x' h5ce ,c3 ,c' tan x 3 tan x' ,?is means t ! curr5ts pass+ ?r\gh ! coil ( a tang5t galvanomet] are proportional1 n to ! angle ( deflection1 b to ! tang5t ( t angle4 ,illu/ration3 ,fig4 #eai4--;,diagram illu/rat+ ! tang5t law4 ,?is is ! law ( ! comb9$ action ( two magnetic fields ^u a magnetic ne$le4 ,if two magnetic fields be at "r angles 9 direction z indicat$ 9 ! figure1 ! resultant field is obta9$ by ! p>allelogram ( =ces & x makes an angle !ta ) "o ( ! compon5t fields su* t tan !ta ,m ,h :]e ,m & ,h are ! /r5g?s ( ! compon5t fields4 ,9 ! tang5t galvanomet] ?is pr9ciple is employ$ 9 ! measurem5t ( curr5ts4 ,a magnetic ne$le is pivot$ 9 a field ( kn[n /r5g?4 ,! curr5t to be measur$ is pass$ r\nd a coil 7or coils7 :i* g5]ates a field at "r angles to ! orig9al field4 ,! ne$le !n lies along ! direction ( ! resultant field1 & by f9d+ ! tang5t ( its angle ( deflection1 & kn[+ ! field /r5g? produc$ by unit curr5t 9 ! coil1 ! curr5t /r5g? c be f\nd4 ,illu/ration3 ,fig4 #ebj4--;,graduation ( tang5t galvanomet] scale ) divisions repres5t+ tang5t values4 ,9 ! figure let a tang5t ,,ot be drawn to ! circle1 & along ?is l9e let any numb] ( equal divisions be set (f1 beg9n+ at ,o4 ,f ^! po9ts draw l9es back to ! c5t]4 ,! circle w ?us be divid$ into a numb] ( spaces1 ( :i* ^? ne> ,o are ne>ly equal1 b :i* get small] & small] z !y rec$e f ,o4 ,^! unequal spaces correspond to equal increm5ts ( ! tang5t4 ,if ! scale 7 divid$ ?us1 ! read+s w\ld be proportional to ! tang5ts4 ,ques4 ,^u :at does ! s5sibility ( a tang5t galvanomet] dep5d8 ,ans4 ,x is directly proportional to ! numb] ( turns ( ! coil & inv]sely proportional to ! diamet] ( ! coil4 ,ques4 ,h[ may ! tang5t galvanomet] be us$ z an ammet]8 ,ans4 ,! /r5g? ( ! curr5t may be calculat$ 9 amp]es by ! =mula giv5 bel[ :5 ! dim5sions ( ! in/rum5t are kn[n4 ,! ne$le is suppos$ to be subject to only ! e>?'s magnetism & to move 9 a horizontal plane4 ,! curr5t is calculat$ z foll[s3 7#a7 amp]es 77,h r7_/,n7 tan x 9 :i* ,h con/ant f table bel[2 r radius ( coil2 ,n numb] ( turns ( coil2 x angle ( deflection ( ne$le4 ,! con/ant ,h1 giv5 9 ! foll[+ table repres5ts ! horizontal =ce ( ! e>?'s magnetism = ! place :]e ! galvanomet] is us$4 ,ea* value has be5 multipli$ by 7#bpi7_/#aj s t ! =mula 7#a7 = amp]es is correct z giv54 ,table ( ,galvanomet] ,con/ants4--,values ( ,h4 ,bo/on 4#fii ,*icago 4#gei ,d5v] 4#iai ,jacksonville #a4jid ,london 4#gde ,m9neapolis 4#fha ,new ,york 4#gdd ,new ,hav5 4#gca ,philadelphia 4#ghc ,portl&1 ,me4 4#fgd ,san ,francisco #a4jba ,/4 ,l\is 4#hga ,wa%+ton 4#haj ,illu/ration3 ,fig4 #eba4--,me*anical explanation ( ! tang5t law4 ,con/ruct an app>atus z %[n 9 ! figure4 ,! %ort wood5 block1 ,,ns1 repres5ts ! magnetic ne$le4 ,?is piece ( wood turns ar\nd its c5t]1 ,c1 :i* may be an ord9>y nail4 ,x w n[ be se5 t two diff]5t =ces act ^u ,n2 namely1 ! weight1 ,g 7"o or two ounces71 & ! *angeable weights :i* are plac$ 9 ! scoop1 ,w 7made ( c>dbo>d74 ,! height ( ! roll1 or :eel1 ,r1 is su* t ! cord1 ,,rn1 runs horizontally1 :5 ,,ns /&s v]tically1 i4e41 :5 !re is no weight 9 ! little scoop4 ,if ! :eel1 ,r1 be plac$ suffici5tly f> f ,,ns1 ! /r+ ,,rn1 w always rema9 almo/ horizontal1 ev5 if ,,ns be deviat$4 ,! ?9 h& on ,,ns moves ov] a v]tical scale1 :i* is divid$ into equal p>ts1 z %[n4 ,?is scale may be made ( c>dbo>d4 ,if ! h& po9t to division #a :5 "o ounce is plac$ 9 ! scoop1 x w po9t to #b = two ounces1 to #c = ?ree ounces1 etc4 ,at #de ! ne$le is deviat$ at its greate/ angle1 & ?is is1 !re=e1 ! s5sitivity angle ( ! tang5t galvanomet]4 ,! deviat+ values are1 !re=e1 proportionate to ! scale p>ts #ja1 #jb1 & #jc1 & s on2 &1 inasmu* z ^! !mselves are tang5ts1 ! tang5t law w hold good4 ,ques4 ,h[ is ! tang5t galvanomet] con/ruct$ to give direct read+s8 ,ans4 ,to obviate ref]5ce to a table1 ! circul> scale ( ! in/rum5t is sometimes graduat$ into tang5t values1 z 9 fig4 #ebj1 in/ead ( be+ divid$ into equal degrees4 ,illu/ration3 ,fig4 #ebb4--,que5 tang5t & s9e galvanomet]4 ,?is in/rum5t prop]ly adju/$ c be us$ z a /&>d in/rum5t = laboratory "w4 ,! brass r+ is #ab in*es 9 diamet]1 & ! grooves 9 :i* ! wire is w\nd are c>efully turn$ s z to be ( true rectangul> cross section1 ?us all[+ ! con/ant ( ! in/rum5t to be accurately calculat$ & comp>$ ) ! con/ant z obta9$ by o!r me?ods4 ,! compass box is #e in*es 9 diamet] & is s held 9 position t x may be rais$ or l[]$1 rotat$ on its v]tical axis1 %ift$ out ( ! plane ( ! coil1 etc41 ?us enabl+ ! op]ator to acquire pr(ici5cy ) ! in/rum5t & to meet all cases ( d]angem5t possible4 ,! dial is graduat$ to s+le degrees1 & ! ne$le is susp5d$ by a v light cocoon fibre4 ,! :ole in/rum5t c be turn$ ab\t its v]tical axis1 & a quadrant graduat$ 9 degrees ^u ! base all[s ! am\nt ( rotation to be accurately measur$1 & ! laws ( ! s9e galvanomet] inve/igat$4 ,! in/rum5t is w\nd to measure 4#be amp]e to #h amp]es4 ,ques4 ,:at is ! objection to ! scale ) tang5t values8 ,ans4 ,x is m difficult to divide an arc into tang5t l9es ) accuracy ?an into equal degrees4 ,ques4 ,:at disadvantage has ! tang5t galvanomet]8 ,ans4 ,! coil be+ mu* l>g] ?an ! ne$le1 & h5ce f> away f x1 r$uces ! s5sitiv5ess ( ! in/rum5t4 ,! ,s9e ,galvanomet]4--,?is type ( in/rum5t has a v]tical coil :i* may be rotat$ ar\nd a v]tical axis1 s t x c be made to foll[ ! magnetic ne$le 9 its deflections4 ,9 ! s9e galvanomet]1 ! coil is mov$ s z to foll[ ! ne$le until x is p>allel ) ! coil4 ,"u ^! circum/ances1 ! /r5g? ( ! deflect+ curr5t is proportional to s9e ( angle ( deflection4 ,illu/ration3 ,fig4 #ebc4--;,c5tral ,sci5tific ,co4 univ]sal tang5t galvanomet]4 ,?is in/rum5t may be us$ z a tang5t1 ,gauga91 ,helmholtz-,gauga91 s9e1 cos9e1 ,wi$emann or detector galvanomet]4 ,! coils1 :i* slide on a beam p>allel to ! "o c>ry+ ! ne$le box1 are w\nd on brass r+s #ab in*es 9 diamet]4 ,on ea* r+ are w\nd two coils ( #dh turns ea*1 connect$ to sep>ate b9d+ po/s1 & d\ble w\nd s z to be ( equal resi/ance4 ,! coils & ne$le box are ea* provid$ ) an indicator = read+ _! position on ! scale4 ,! ne$le box is swivell$ & removable & "o coil may be rotat$ ab\t its v]tical axis & its position read on a disc graduat$ 9 degrees4 ,curr5ts may be measur$ rang+ f 4#jjjjjb amp]e to #ajj amp]es4 ,ques4 ,describe ! con/ruction ( a s9e galvanomet]4 ,ans4 ,a =m ( s9e galvanomet] is %[n 9 fig4 #ebd4 ,! v]tical wire coil is se5 at ,m4 ,a ne$le ( any l5g? less ?an ! diamet] ( ! coil ,m1 moves ov] ! graduat$ circle ,n4 ,! coil ,m1 & graduat$ circle ,n may be rotat$ on a v]tical axis1 & ! am\nt ( angul> movem5t necess>y to br+ ! ne$le to z]o1 measur$ on ! graduat$ circle ,h4 ,ques4 ,h[ is ! curr5t /r5g? measur$8 ,ans4 ,x is proportional to ! s9e ( ! angle measur$ on ! horizontal circle ,h1 ?r\gh :i* x is necess>y to turn ! coil ,m1 f ! plane ( ! e>?'s magnetic m]idian to ! plane ( ! ne$le :5 x is n fur!r deflect$ by ! curr5t4 ,illu/ration3 ,fig4 #ebd4--,s9e galvanomet]4 ,x diff]s f ! tang5t galvanomet] 9 t ! v]tical coil & magnetic ne$le are m\nt$ ^u a /&>d free to revolve ar\nd a v]tical axis1 ) provision = det]m9+ ! angul> position ( ! coil4 ,! ne$le may be ( any l5g? %ort] ?an ! diamet] ( ! coil4 ,9 ! figure ! p>ts are3 ,m1 coil2 ,n1 graduat$ dial ( magnetic ne$le2 ,h1 graduat$ dial by :i* ! am\nt ( rotation necess>y to br+ ! ne$le to z]o is measur$2 ,e1 t]m9als ( ! coil2 ,o1 upright /&>d c>ry+ coil & graduat$ dial ( magnetic ne$le2 ,c1 base ) levell+ screws4 ,ques4 ,h[ is ! s9e galvanomet] op]at$8 ,ans4 ,9 us+ ! in/rum5t1 aft] ! ne$le has be5 set to z]o1 ! curr5t is s5t ?r\gh ! coil1 produc+ a deflection ( ! ne$le4 ,! coil is !n rotat$ to foll[ ! motion ( ! ne$le1 ! curr5t be+ kept con/ant1 ! rotation be+ cont9u$ until ! z]o on ! upp] dial aga9 regi/]s ) ! ne$le4 ,! curr5t !n is proportional to ! s9e ( ! angle ?r\gh :i* ! coil has be5 turn$1 z det]m9$ by ! l[] dial4 ,ques4 ,has ! s9e galvanomet] a l>ge range8 ,ans4 ,= a giv5 controll+ field1 x does n admit ( a v l>ge range ( curr5t measurem5t1 s9ce1 = l>ge deflection1 on rotat+ ! coil ! position ( in/ability is soon rea*$4 ,,table ,,( ,,natural ,,s9es ,,& ,,tang5ts ,angle ,s94 ,tan4 #j 4#jjjj 4#jjjj #a 4#jage 4#jage #b 4#jcdi 4#jcdi #c 4#jebc 4#jebd #d 4#jfih 4#jfii #e 4#jhga 4#jhge #f 4#ajde 4#ajea #g 4#abai 4#abbh #h 4#acib 4#adje #i 4#aefd 4#aefd #aj 4#agcf 4#agfc #aa 4#aijh 4#aidd #ab 4#bjgi 4#babf #ac 4#bbej 4#bcji #ad 4#bdai 4#bdic #ae 4#behh 4#bfgi #af 4#bgef 4#bhfg #ag 4#bibd 4#cjeg #ah 4#cjij 4#cbdi #ai 4#cbef 4#cddc #bj 4#cdbj 4#cfdj #ba 4#cehd 4#chci #bb 4#cgdf 4#djdj #bc 4#cijg 4#dbde #bd 4#djfg 4#ddeb #be 4#dbbf 4#dffc #bf 4#dchd 4#dhgg #bg 4#dedj 4#ejie #bh 4#dfie 4#ecag #bi 4#dhdh 4#eedc #cj 4#ejjj 4#eggd #ca 4#eaej 4#fjji #cb 4#ebii 4#fbdi #cc 4#eddf 4#fdid #cd 4#eeib 4#fgde #ce 4#egcf 4#gjjb #cf 4#ehgh 4#gbfe #cg 4#fjah 4#gecf #ch 4#faeg 4#ghac #ci 4#fbic 4#hjih #dj 4#fdbh 4#hcia #da 4#fefa 4#hfic #db 4#ffia 4#ijjd #dc 4#fhbj 4#icbe #dd 4#fidg 4#ifeg #de 4#gjga #a4jjjj #df 4#gaic #a4jcee #dg 4#gcad #a4jgbd #dh 4#gdca #a4aajf #di 4#gedg #a4aejd #ej 4#gffj #a4aiah #ea 4#ggga #a4bcdi #eb 4#ghhj #a4bgii #ec 4#gihf #a4cbgj #ed 4#hjij #a4cgfd #ee 4#haib #a4dbha #ef 4#hbij #a4dhbf #eg 4#hchg #a4ecii #eh 4#hdhj #a4fjjc #ei 4#hegb #a4ffdc #fj 4#hffj #a4gcba #fa 4#hgdf #a4hjdj #fb 4#hhbi #a4hhjg #fc 4#hiaj #a4ifbf #fd 4#hihh #b4jejc #fe 4#ijfc #b4adde #ff 4#iace #b4bdfj #fg 4#ibje #b4ceei #fh 4#ibgb #b4dgea #fi 4#icci #b4fjea #gj 4#icig #b4gdge #ga 4#idee #b4ijdb #gb 4#ieaa #c4jggb #gc 4#iefc #c4bgji #gd 4#ifac #c4dhgd #ge 4#ifei #c4gcba #gf 4#igjc #d4jajh #gg 4#igdd #d4ccae #gh 4#igha #d4gjdf #gi 4#ihaf #e4addf #hj 4#ihdh #e4fgac #ha 4#ihgg #f4cach #hb 4#iijc #g4aaed #hc 4#iibe #h4addc #hd 4#iide #i4eadd #he 4#iifb #aa4dc #hf 4#iigf #ad4cj #hg 4#iihf #ai4jh #hh 4#iiid #bh4fd #hi 4#iiih #eg4bi ,ques4 ,:at is ! position ( in/ability8 ,ans4 ,! position ( ! ne$le beyond :i* ! rotation ( ! coil w cause x to turn all ! way r\nd4 ,ques4 ,h[ may ! range be increas$8 ,ans4 ,by an adju/able controll+ field or a %unt4 ,ques4 ,:at advantage has ! s9e galvanomet] ov] ! tang5t in/rum5t8 ,ans4 ,its advantage is 9 ! case :]e ! relative values ( two or m curr5ts are requir$ to be measur$1 or :]e ! con/ant ( ! in/rum5t is obta9$ by comp>ison ) a /&>d measur+ in/rum5t & n calculat$ f ! dim5sions ( ! coil1 because all galvanomet]s ?us us$ foll[ ! s9e law indep5d5tly ( ! %ape ( ! coil1 :ile only circul> coils w foll[ ! s9e law4 ,illu/ration3 ,fig4 #ebe4--;,diff]5tial galvanomet]4 ,x consi/s ( two coils ( wire1 s w\nd z to h opposite magnetic effects on a magnetic ne$le susp5d$ c5trally betwe5 !m4 ,! ne$le ( a diff]5tial galvanomet] %[s no deflection :5 two equal curr5ts are s5t ?r\gh ! coils 9 opposite directions1 s9ce1 "u ^! conditions1 ea* coil neutralizes ! effect ( ! o!r4 ,sometimes ! curr5t is s s5t ?r\gh ! two coils1 t ea* coil deflects ! ne$le 9 ! same direction4 ,9 ?is case ! in/rum5t is no long] diff]5tial 9 action4 ,if1 :5 ?is condition obta9s1 ! magnetic ne$le be susp5d$ at ! exact c5t] ( ! l9e :i* jo9s ! c5t]s ( ! coils1 ! advantage is ga9$ by obta9+ a field ( m ne>ly uni=m int5sity ar\nd ! ne$le4 ,:5 ! ne$le is susp5d$ by a silk fibre1 a f9al & mo/ delicate adju/m5t c be obta9$ by rais+ or l[]+ "o ( ! levell+ screws slightly1 s z to tilt ! ne$le ne>] to or f>!r f "o ( ! coils4 ,! ,diff]5tial ,galvanomet]4--,?is is a =m ( galvanomet] 9 :i* a magnetic ne$le is susp5d$ betwe5 two coils ( equal resi/ance s w\nd z to t5d to deflect ! ne$le 9 opposite directions4 ,! ne$le ( a diff]5tial galvanomet] %[s no deflection :5 two equal curr5ts are s5t ?r\gh ! coils 9 opposite directions1 s9ce "u ^! conditions1 ea* coil neutralizes ! o!r's effects4 ,su* in/rum5ts may be us$ 9 comp>+ resi/ances1 al?\gh ! ,:eat/one bridge1 9 mo/ cases1 af=ds a pref]able me?od4 ,ques4 ,:at is ! special use ( ! diff]5tial galvanomet]8 ,ans4 ,x is us$ = comp>+ two curr5ts4 ,ques4 ,:at is ! me?od ( comp>+ curr5ts8 ,ans4 ,if two equal curr5ts be s5t 9 opposite directions ?r\gh ! coils ( ! galvanomet]1 ! ne$le w n move2 if ! curr5ts be unequal1 ! ne$le w be deflect$ by ! /rong] ( !m ) an int5sity correspond+ to ! diff]5ce ( ! /r5g?s ( ! two curr5ts4 ,ques4 ,h[ are ! coils adju/$8 ,ans4 ,?is is done by c\pl+ !m 9 s]ies 9 su* a way t !y t5d to turn ! ne$le 9 opposite directions1 & :5 a curr5t is pass+ ?r\gh !m1 !y are mov$ ne>] to ! ne$le or f>!r f x until ! ne$le /&s at z]o ) any curr5t4 ,if ! coils be n movable1 a turn or m c be unw\nd f ! coil giv+ ! greate/ magnetic effect until a balance is obta9$1 ! wire s unw\nd c !n be coil$ 9 ! base ( ! in/rum5t4 ,balli/ic ,galvanomet]4--,?is type ( galvanomet] is design$ to measure ! /r5g? ( mom5t>y curr5ts1 su* = in/ance1 z ! dis*>ge ( a cond5s]4 ,9 con/ruction ! magnetic sy/em is giv5 consid]able weight1 & arrang$ to give ! lea/ possible damp+ effect4 ,! t]m damp+ effect means ! (f]+ ( a ret>d+ =ce to control sw++ vibrations1 su* z ! movem5ts ( a galvanomet] ne$le1 & to br+ !m quickly to re/4 ,if a mom5t>y curr5t be pass$ ?r\gh a balli/ic galvanomet]1 ! impulse giv5 to ! ne$le does n cause appreciable movem5t to ! magnetic sy/em until ! curr5t ceases1 ow+ to ! in]tia ( ! heavy mov+ p>ts1 ! result be+ a sl[ sw+ ( ! ne$le4 ,illu/ration3 ,fig4 #ebf4--,que5 dead beat & balli/ic reflect+ galvanomet]4 ,z illu/rat$1 ! coils are easily removable & enclose a heavy block ( copp] fix$ 9 a c5tral =k4 ,9 a cyl9drical hole bor$ 9 ?is block hangs ! bell magnet :i* ) its mirror is susp5d$ by a long cocoon fibre1 & ! eddy curr5ts induc$ 9 ! copp] br+ ! sy/em quickly to re/ aft] a deflection4 ,by lift+ ! copp] block out ( ! frame ! in/rum5t is made balli/ic4 ,! in/rum5t is made ) coils ( any desir$ resi/ance up to #a1jjj ohms4 ,ques4 ,:at "n is giv5 to ! sw+ ( a balli/ic galvanomet] ne$le8 ,ans4 ,x is call$ ! kick4 ,ques4 ,h[ is ! curr5t measur$8 ,ans4 ,z ! ne$le sw+s sl[ly ar\nd x adds up1 z x 71 ! v>y+ impulses receiv$ dur+ ! passage ( ! mom5t>y curr5t1 & ! quantity ( electricity t has pass$ is proportional to ! s9e ( half ! angle ( ! fir/ sw+ or kick4 ,if a reflect+ me?od be us$ ) a /raight scale1 ! obs]v$ deflection dep5ds ^u ! tang5t ( twice ! angle ( movem5t ( ! ne$le4 ,= small deflections1 h[ev]1 ! *ange ( flux c be tak5 z directly proportional to ! obs]v$ deflection4 ,illu/ration3 ,fig4 #ebg4--,?ompson galvanomet] ) mirror reflect+ sy/em = read+ ! deflections ( a galvanomet] ne$le by ! movem5ts ( a spot ( light reflect$ f a mirror atta*$ to ! ne$le or movable magnetic sy/em4 ,use ( ,mirrors 9 ,galvanomet]s4--,9 ord] t small curr5ts may be measur$ accurately1 "s means mu/ be provid$ to easily read a small deflection ( ! ne$le4 ,accord+ly1 x is desirable t ! po9t] be v long s t a l>ge numb] ( scale divisions may correspond to small deflections4 ,9 con/ruction1 s9ce s5sitive galvanomet]s mu/ be made ) ! mov+ p>ts ( little weight1 x w\ld n d to use a long ne$le1 h5ce a ray ( light is us$ in/ead1 :i* is reflect$ on a di/ant scale by a small mirror atta*$ to ! mov+ "p4 ,9 ! ,?ompson mirror reflect+ galvanomet]1 z %[n 9 fig4 #ebh1 a small v]tical slit is cut 9 ! lamp scre5 bel[ ! scale1 & ! ray ( light f ! lamp1 pass+ ?r\gh ! slit1 /rikes ! mirror :i* is ab\t ?ree feet di/ant1 & :i* reflects ! beam back to ! scale4 ,x %\ld be not$ t ! angle betwe5 ! orig9al ray ( light & ! reflect$ ray is twice ! angle ( ! deflection ( ! mirror2 ! deflections ( ! ray ( light on ! scale1 h[ev]1 are practically proportional to ! /r5g? ( curr5ts ?r\gh ! in/rum5t4 ,! mirror arrangem5t z %[n 9 fig4 #ebh1 requires a d>k5$ room = its op]ation1 b su* is n necess>y :5 a telescope is us$ z 9 fig4 #ebi4 ,"h ! scale read+s are reflect$ 9 ! mirror & _! value obs]v$ by ! telescope )\t artificial light4 ,illu/ration3 ,fig4 #ebh4--,telescope me?od ( read+ galvanomet] deflections by reflection ( scale read+ 9 mirror4 ,"h two mirrors are us$1 b 9 mo/ cases ! telescope is po9t$ directly t[>d ! mirror on galvanomet] %[n 9 fig4 #ebg1 because ! two mirror sy/em1 z illu/rat$ 9 ! figure1 is us$ on portable galvanomet]s s9ce x is ! m compact4 ,damp+4--,?is relates to ! *eck+ or r$uction ( oscillations4 ,?us1 a galvanomet] is said to be damp$ :5 s con/ruct$ t any oscillations ( ! po9t] :i* may be />t$1 rapidly die away4 ,galvanomet]s are frequ5tly provid$ ) damp+ devices = ! purpose ( annull+ ^! oscillations1 ?us caus+ ! mov+ "p to assume its f9al position z quickly z possible4 ,sometimes ! in/rum5t is fitt$ ) a damp+ coil1 or clos$ coil s arrang$ ) respect to ! mov+ sy/em t ! oscillations ( ! latt] give rise to electric curr5ts 9 ! clos$ coil1 :]eby en]gy is dissipat$4 ,aga91 air vanes are employ$1 b any?+ 9 ! nature ( solid friction _c be us$4 ,illu/ration3 ,figs4 #ebi & #ecj4--;,galvanomet] lamp & scale = individual use4 ,! scale is et*$ on a gr\nd glass /rip #f c5timet]s wide by #fj c5timet]s long ) long c5timet] divisions & %ort millimet] divisions ! entire l5g?1 read+ bo? ways f z]o 9 ! c5t]4 ,x is m\nt$ 9 an adju/able wood5 frame4 ,a /raight filam5t lamp 7#aaj volts7 is enclos$ 9 a metal hood japann$ black to cut out all reflect$ light4 ,?is =m ( filam5t makes a s+le brilliant l9e on ! scale1 enabl+ clos] read+s ?an ! spot ( light arrangem5t4 ,! lamp hood is adju/able to any desir$ height on ! support rod4 ,d',arsonval ,galvanomet]4--,?is in/rum5t has a movable coil 9 place ( a ne$le1 & its op]ation dep5ds ^u ! pr9ciple t if a flat coil ( wire be susp5d$ ) its axis p]p5dicul> to a /rong magnetic field1 x w be deflect$ :5ev] a curr5t ( electricity passes ?r\gh x4 ,ques4 ,describe ! con/ruction ( a ,d',arsonval galvanomet]4 ,ans4 ,! ess5tial features are %[n 9 figs4 #ecb & #ecc4 ,! coil1 :i* is rectangul> 9 section is w\nd ^u a copp] =m1 & susp5d$ betwe5 a p]man5t magnet by f9e wires to ! po9ts ,a & ,b4 ,! magnet has its poles at ,n & ,s4 ,x is a s(t iron cyl9d] fix$ betwe5 ! poles 9 ord] to int5sify ! magnetic field across ! air gaps 9 :i* ! coil moves4 ,illu/ration3 ,fig4 #eca4--,que5 read+ telescope4 ,?is arrangem5t is utiliz$ to measure ! deflections ( a galvanomet] hav+ susp5d$ mirror mov+ sy/em4 ,x consi/s ( a read+ telescope m\nt$ z illu/rat$ ) a millimet] scale1 hav+ a l5g? ( #ej c5timet]s4 ,9 use1 ! image ( ! scale is se5 9 ! galvanomet] mirror ?r\gh ! telescope4 ,! eye piece ( ! telescope has a cross hair :i* acts z a ref]5ce l9e s t by not+ ! p>ticul> division on ! scale :5 ! galvanomet] is at re/1 ! am\nt ( deflection c be readily obs]v$ :5 ! galvanomet] is deflect$4 ,! in/rum5t has all ! necess>y adju/m5ts to set x up quickly & = br++ ! cross hair & scale 9 focus4 ,x is g5]ally plac$ at a di/ance ( "o met] f ! galvanomet] mirror4 ,ques4 ,expla9 its op]ation4 ,ans4 ,an enl>g$ horizontal cross section ( ! galvanomet] on l9e ,,xy is %[n 9 fig4 #ecc4 ,! curr5t is fl[+ 9 ! coil z 9 fig4 #ecb1 up on ! left side & d[n on ! "r4 ,! position ( ! coil :5 no curr5t is fl[+ is indicat$ by n' s'4 ,by apply+ ! law ( mutual action betwe5 magnetic poles1 x is se5 t :5 ! curr5t is appli$1 ! poles develop$ at n' s' w move into ! position n'' s''4 ,see fig4 #aai4 ,ques4 ,h[ is ! coil affect$ by a *ange 9 ! direction ( ! curr5t8 ,ans4 ,! pol>ity ( ! coil is rev]s$ & consequ5tly ! direction ( ! deflection4 ,illu/ration3 ,figs4 #ecb & #ecc4--;,diagrams %[+ ess5tial features ( con/ruction & pr9ciple ( op]ation ( ,d',arsonval galvanomet]4 ,ques4 ,^u :at does ! s5sitiv5ess ( ! in/rum5t dep5d8 ,ans4 ,^u ! /r5g? ( ! field ( ! p]man5t magnet1 ! numb] ( turns 9 ! susp5d$ coil1 & ! torsion ( ! wires by :i* x is susp5d$4 ,ques4 ,:5 is ?is galvanomet] call$ dead beat8 ,ans4 ,:5 ! con/ruction is su* t ! mov+ "p comes quickly to re/ )\t a s]ies ( dim9i%+ vibrations4 ,illu/ration3 ,figs4 #ecd to #ecf4--,que5 horizontal magnet ,d',arsonval galvanomet] ) telescope & scale4 ,x is v s5sitive & is us$ 9 _m electrical measurem5ts1 includ+ comm]cial te/+1 su* z measur+ insulation ( cables1 fault location1 etc4 ,x is n affect$ by surr\nd+ magnetic di/urbances1 & may1 !re=e1 be us$ 9 proximity to dynamos & swit*bo>ds4 ,! in/rum5t has a pair ( b9d+ po/ t]m9als1 "o ( :i* connects to a bottom spiral ( ! sy/em & ! o!r =ms a junction ) ! top ( ! tube hold+ ! sy/em1 =m+ a complete circuit ?r\gh ! coil4 ,! tube conta9+ ! sy/em may be readily remov$ f ! magnet & ano!r tube hav+ a diff]5t sy/em ins]t$ z is requir$ = v>i\s k9ds ( electrical measurem5t4 ,! entire sy/em ) its susp5sion may be inspect$ by ! removal ( a ?umb screw4 ,to inspect int]ior ( tube fir/ be sure t ! screw ,b is turn$ s t ! coil is clamp$4 ,entirely remove screw ,c1 &1 hold+ ! outside tube ne> ! w9d[1 press firmly ) ! f+] on ! extreme top ( ! susp5sion support4 ,! inside rib1 ) complete susp5sion1 w draw f ! tube1 & ! work+ p>ts c be fully inspect$4 ,c>efully return same to its orig9al position 9 tube1 sett+ tight ! screw ,c4 ,! galvanomet] is design$ s t ! coil is clamp$ 9 position :5 ! galvanomet] mu/ be transport$4 ,! insulation ( ! galvanomet] t]m9als & b9d+ po/s is su* z to gu>d aga9/ any possible leakage4 ,z a fur!r protection1 ea* levell+ screw is provid$ ) a h>d rubb] insulator4 ,?is feature is ess5tial s9ce1 9 mak+ insulation measurem5ts1 ! op]ator wi%es to be assur$ t ! deflection be+ obta9$ is ! result ( leakage ^u ! cable or wire be+ measur$ & n leakage betwe5 ! galvanomet] t]m9als4 ,! galvanomet] is provid$ ) an atta*$ telescope & scale = not+ ! deflections4 ,! deflections produc$ by ?is galvanomet] are proportional to ! curr5t4 ,to facilitate quickly sett+ up ! in/rum5t1 two way levels are provid$4 ,ques4 ,:at causes ?is8 ,ans4 ,! in/rum5t is made dead beat by w9d+ ! coil on a copp] or alum9um frame1 s t :5 9 op]ation1 curr5ts are induc$ 9 ! frame by ! motion ( ! coil 9 ! magnetic field2 ^! curr5ts oppose ! motion ( ! coil4 ,ques4 ,= :at s]vice is ! ,d',arsonval galvanomet] adapt$8 ,ans4 ,x is desirable = g5]al use z x is n mu* affect$ by *anges 9 ! magnetic field4 ,x may be made ) high en\gh p]iod & s5sibility to be satisfactory z a balli/ic in/rum5t1 b = extreme s5sibility an in/rum5t ( ! a/atic type is m g5]ally us$4 ,galvanomet] ,con/ant or ,figure ( ,m]it4--,9 ord] t a galvanomet] %all be ( value z a measur+ in/rum5t1 ! relation betwe5 ! curr5t & ! deflection produc$ by x mu/ be kn[n4 ,?is may be obta9$ exp]im5tally by det]m9+ ! value ( ! curr5t requir$ to produce "o scale division4 ,! galvanomet] con/ant !n may be def9$ z ! resi/ance ?r\gh :i* ! galvanomet] w give a deflection ( "o scale division :5 ! curr5t appli$ is at a pressure ( "o volt4 ,accord+ly1 ! deflection z indicat$ on ! scale mu/ be multipli$ by its con/ant or figure ( m]it1 9 ord] to obta9 ! correct read+4 ,if ! scale read+s be n directly proportional to ! quantity to be measur$1 ! law ( ! in/rum5t mu/ also be consid]$4 ,?us 9 a tang5t galvanomet] z previ\sly expla9$ ,i ,k tan phi :]e ,i curr5t1 phi ! deflection or scale read+1 & ,k ! galvanomet] con/ant4 ,illu/ration3 ,fig4 #ecg4--;,diagram %[+ me?od ( connect+ galvanomet] %unt4 ,by ! use ( a %unt ! range ( measurem5t ( a galvanomet] c be greatly increas$4 ,illu/ration3 ,fig4 #ech4--;,diagram ( a =m ( univ]sal %unt box = use ) galvanomet]s ( widely diff]5t resi/ances4 ,! galvanomet]1 z indicat$ at ,g1 is connect$ across ! ends ( a s]ies ( resi/ances ,,ab4 ,! ma9 wires are connect$1 "o to end ,a ( ! s]ies & ! o!r to a travell+ po9t ^: position is v>i$ by means ( plugs or by a dial swit*4 ,galvanomet] ,%unts4--,! s5sitiv5ess ( a galvanomet] us$ = measur+ curr5t may be r$uc$ to any desir$ ext5t by connect+ a resi/ance ( kn[n value 9 p>allel ) x4 ,?us1 if x be desir$ to measure a curr5t great] ?an c be measur$ directly by ! galvanomet]1 a "p ( ! curr5t c be s5t ?r\gh ! resi/ance or %unt1 & ! total value ( ! curr5t calculat$4 ,a galvanomet] %unt be>s a def9ite ratio to ! resi/ance ( ! galvanomet]1 be+ usually adju/$ s t only 4#a1 4#ja1 or 4#jja "p ( ! curr5t passes ?r\gh ! galvanomet]4 ,! degree 9 :i* a %unt increases ! range ( deflection ( a galvanomet] is call$ its multiply+ p[]4 ,illu/ration3 ,fig4 #eci4--;,ayrton-,ma!r univ]sal %unt4 ,?is %unt may be us$ ) any galvanomet]4 ,! total resi/ance is #aj1jjj ohms1 ) %unt p[]s ( #a1 #e1 #aj1 #ej1 #ajj1 #ejj1 & #a1jjj4 ,x is also fitt$ ) positions 9 :i* ! galvanomet] is %ort$ & (f4 ,! coils are ( con/antan wire4 ,if 4#a ( ! curr5t fl[+1 pass$ ?r\gh ! galvanomet] & 4#i ?r\gh ! %unt1 !n ! curr5t 9 ! circuit w\ld be t5 times t ?r\gh ! galvanomet]4 ,accord+ly ! curr5t 9 ! galvanomet] mu/ be multipli$ by ! multiply+ p[] ( ! %unt to obta9 ! true value ( ! curr5t 9 ! circuit4 ,9 ord] to det]m9e ! resi/ance necess>y to be us$ ) a c]ta9 galvanomet]1 ! resi/ance ( ! latt] is to be divid$ by ! multiply+ p[] desir$ less "o4 ,,example4--,:at mu/ be ! resi/ance ( a %unt = a galvanomet] ( #b1jjj ohms resi/ance :]e only "o fif? ( ! curr5t is to pass ?r\gh ! galvanomet]8 ,! multiply+ p[] less "o is #e - #a #d & ! requir$ resi/ance is #b1jjj #d #ejj ohms4 ,:5 x is ess5tial t ! total resi/ance ( ! circuit %\ld n be alt]$ by an alt]nation ( ! galvanomet] %unt1 a comp5sat+ box %\ld be us$ :i* automatically ins]ts a resi/ance = ea* %unt 9 s]ies ) ! %unt$ galvanomet] to br+ ! total resi/ance up equal to ! un%unt$ value4 ,?us ! curr5t 9 ! ma9 circuit is n alt]$4 ,,*apt] ,,xxvii ,,te/+ ,,& ,,te/+ ,,app>atus ,! practical electrician frequ5tly has to make te/s ( v>i\s k9ds :i* require ! rapid & accurate measurem5t ( voltage1 curr5t & resi/ance4 ,x is !re=e ess5tial t he und]/& ! me?ods employ$ 9 te/+ & ! op]ation ( ! in/rum5ts us$4 ,mo/ te/s are made ) a galvanomet]1 & ! devices1 su* z resi/ances1 swit*es1 etc41 :i* are us$ 9 connection ) ! galvanomet] may be obta9$ put up 9 a neat & sub/antial box toge!r ) ! galvanomet]1 ! comb9ation be+ call$ a te/+ set4 ,num]\s =ms ( te/+ set are illu/rat$ 9 ?is *apt]4 ,! con/ruction1 use1 & op]ation ( ! v>i\s types ( galvanomet] h be5 expla9$ 9 *apt] tw5ty-six4 ,ammet]s & voltmet]s1 :i* are simply special =ms ( galvanomet]1 & :i* are l>gely us$ are fully describ$ 9 ! prec$+ *apt]4 ,pressure ,measurem5t4--,an electromotive =ce has be5 def9$ z t :i* causes or t5ds to cause a curr5t2 x is analog\s to wat] pressure2 pot5tial diff]5ce corresponds to diff]5ce ( level4 ,! total electromotive =ce ( a circuit is indep5d5t ( resi/ance or curr5t1 & _c be limit$ to mean ! fall ( pressure betwe5 any two po9ts1 z = in/ance ! t]m9als ( a batt]y4 ,if ! pressure ( a batt]y be two volts :5 measur$ on op5 circuit by a /atic voltmet]1 !re w /ill be two volts on clos$ circuit1 b !re w n[ be a loss ( pressure ?r\gh ! int]nal resi/ance ( ! batt]y & ! voltage across ! t]m9als w be less ?an ! total voltage4 ,! /atic voltmet]1 nev] clos+ ! circuit1 actually measures ! total voltage4 ,illu/ration3 ,fig4 #edj4--;,cl>k cell 7,kahle's modification ( ! ,rayleigh ,h =m71 ! /&>d = ! ,int]national volt4 ,! cell has = its positive electrode1 m]cury1 & = its negative electrode1 amalgamat$ z9c4 ,! electrolyte consi/s ( a saturat$ solution ( z9c sulphate & m]cur\s sulphate4 ,! pressure is #a4dcd volts at #ae;,c41 & betwe5 #aj;,c4 & #be;,c4 ! pressure decreases 4#jjaae ( a volt = ea* increase ( #a;,c4 ,! conta9+ glass vessel consi/s ( two limbs1 clos$ at bottom & jo9$ above to a common neck fitt$ ) a gr\nd glass /opp]4 ,! diamet] ( ! limbs %\ld be at lea/ #b cms41 & _! l5g? at lea/ #c cms4 ,! neck %\ld be n less ?an #a4e cms4 9 diamet]4 ,at ! bottom ( ea* limb a plat9um wire ( ab\t 4#d mm4 9 diamet] is seal$ ?r\gh ! glass4 ,to set up ! cell1 place m]cury 9 "o limb1 & 9 ! o!r hot liquid amalgam1 conta9+ #ij p>ts m]cury & #aj p>ts z9c4 ,! plat9um wires at ! bottom mu/ be completely cov]$ by ! m]cury & ! amalgam1 respectively4 ,on ! m]cury1 place a lay] #a cm4 ?ick ( ! z9c & m]cur\s sulphate pa/e4 ,bo? ?is pa/e & ! z9c amalgam mu/ be cov]$ ) a lay] ( ! neutral z9c sulphate cry/als #a cm4 ?ick4 ,! :ole vessel mu/ !n be fill$ ) ! saturat$ z9c sulphate solution1 & ! /opp] ins]t$ s t x %all j t\* x1 leav+1 h[ev]1 a small bubble to gu>d aga9/ breakage :5 ! temp]ature rises4 ,be=e f9ally ins]t+ ! glass /opp] a /rong alcoholic solution ( %ellac is appli$ to ! upp] edge1 aft] :i* ! /opp] is press$ firmly 9 place4 ,ques4 ,:at error is introduc$ 9 measur+ ! pressure ( a batt]y ) an ord9>y voltmet]8 ,ans4 ,s9ce ! measurem5t is made on clos$ circuit ! read+ does n give ! total pressure ( ! batt]y4 ,! error is v slight because ! resi/ance ( ! voltmet] is v high & ! curr5t s small t ! loss ( pressure 9 ! batt]y c be neglect$4 ,illu/ration3 ,fig4 #eda4--,we/on ,cadmium ,cell4 ,x is made 9 two =ms2 "o kn[n z ! ,we/on normal cell1 9 :i* ! solution ( cadmium sulphate is saturat$ at all temp]atures at :i* ! cell may be us$4 ,! o!r1 kn[n z ! ,we/on /&>d cell1 9 :i* ! cadmium sulphate solution is unsaturat$ at all temp]atures above #d;,c4 ,! ,we/on normal cell1 or saturat$ =m is slightly affect$ by *anges 9 temp]ature1 b1 on acc\nt ( ! fact t x c be accurately reproduc$1 x 0 adopt$ by ! ,london ,conf]5ce 9 #aijh1 z a conv5i5t voltage /&>d4 ,! value ( its voltage sugge/$ by ! committee ( ! ,london ,conf]5ce on ,electrical ,units & ,/&>ds1 & adopt$ by ! ,bureau ( ,/&>ds at ,wa%+ton1 ,jan4 #a/1 #aiaa1 is #a4jahc ,int]national volts at #bj;,c4 ,at any o!r temp]ature its voltage is3 ,et ,e#bj - #j4jjjjdjf7t-#bj7 - #j4jjjjjjie7t-#bj7b #j4jjjjjjja7t-#bj7c ,! ,we/on /&>d cell1 or unsaturat$ =m is practically unaffect$ by *anges 9 temp]ature & is ! =m mo/ commonly us$ = laboratory "w & g5]al te/+4 ,! av]age pressure ( ?is =m is #a4jahg ,int4 volts4 ,ques4 ,def9e ! ,int]national volt4 ,ans4 ,x is ! electromotive =ce t1 /eadily appli$ to a conductor ^: resi/ance is "o ,int]national ohm1 w produce a curr5t ( "o ,int]national amp]e1 & :i* is repres5t$ suffici5tly well = practical use by #a1jjj_/a1dcd ( ! voltage betwe5 ! poles ( ! ,cl>k cell at a temp]ature ( #ae ,c41 :5 prep>$ z 9 fig4 #edj4 ,! relation betwe5 ! units volt1 amp]e & ohm1 are %[n graphically 9 figs4 #edb & #edc4 ,illu/ration3 ,figs4 #edb & #edc4--;,diagrams %[+ hydraulic analogy illu/rat+ ! diff]5ce betwe5 amp]es & c\lombs4 ,! rate ( curr5t fl[ ( "o amp]e 9 fig4 #edc may be comp>$ to ! rate ( dis*>ge ( a pump z 9 fig4 #edb4 ,assum+ ! pump to be ( su* size t x dis*>ges a gallon p] /roke & is mak+ #fj /rokes p] m9ute1 ! quantity ( wat] dis*>g$ p] h\r 7c\lombs 9 fig4 #edc7 is #a #fj #fj #c1fjj gallons4 ,foll[+ ! analogy fur!r 79 fig4 #edc71 ! pressure ( "o volt is requir$ to =ce ! electricity ?r\gh ! resi/ance ( "o ohm betwe5 ! t]m9als ,a & ,b4 ,9 fig4 #edb1 ! boil] mu/ furni% /eam pressure on ! pump pi/on to ov]come ! friction 7resi/ance7 (f]$ by ! pipe & raise ! wat] f ! l[] level ,a' to ! high] level ,b'4 ,! diff]5ce ( pressure betwe5 ,a & ,b 9 ! electric circuit corresponds to ! diff]5ce ( pressure betwe5 ,a' & ,b'4 ,! cell furni%es ! en]gy to move ! curr5t by ma9ta9+ a diff]5ce ( pressure at its t]m9als ,c & ,d2 simil>ly1 ! boil] furni%es en]gy to raise ! wat] by ma9ta9+ a diff]5ce ( pressure betwe5 ! /eam pipe ,c & exhau/ pipe ,d'4 ,illu/ration3 ,fig4 #edc4 ,if ! curr5t /r5g? 9 fig4 #edc be "o amp]e1 ! quantity ( electricity pass+ any po9t 9 ! circuit p] h\r is #a #fj #fj #c1fjj c\lombs4 ,curr5t ,measurem5t4--,x is necess>y to adopt "s arbitr>y /&>d 9 ord] to comp>e curr5ts ( diff]5t /r5g?s4 ,! t]m /r5g? ( a curr5t1 or curr5t /r5g? means ! rate ( fl[ pa/ any po9t 9 ! circuit 9 a giv5 unit ( "t4 ,! unit ( curr5t1 call$ ! amp]e1 is def9$ z ! unv>y+ curr5t :i*1 :5 pass$ ?r\gh a solution ( nitrate ( silv] 9 wat] 7#ae p] c5t4 by weight ( ! nitrate7 deposits silv] at ! rate ( 4#jjaaah gramme p] second4 ,illu/ration3 ,fig4 #edd4--,que5 weight voltamet] = det]m9+ ! /r5g? ( curr5t by ! weight ( metal deposit$ 9 a giv5 "t4 ,! two outside plates =m ! anode & are jo9$ toge!r & to "o b9d+ po/1 :ile ! ca?ode is plac$ betwe5 !m & connect$ to ! o!r b9d+ po/4 ,! ca?ode ?us receives a deposit on bo? sides4 ,an adju/able arm s]ves to l[] ! plates into ! electrolyte4 ,to calculate ! /r5g? ( an unkn[n curr5t :i* has pass$ ?r\gh a weight voltamet]1 divide ! ga9 9 weight by ! numb] ( seconds ! curr5t fl[s ?r\gh ! in/rum5t & by ! weight deposit$ by "o amp]e 9 "o second4 ,t is1 curr5t /r5g? 9 amp]es ga9 9 weight 7"t 9 seconds 4#jjjcbhf74 ,ques4 ,h[ mu* copp] or z9c w "o amp]e deposit 9 "o second8 ,ans4 4#jjjcbhf gramme ( copp] 9 a copp] voltamet]1 or 4#jjjcchf gramme ( z9c 9 a z9c voltamet]4 ,ques4 ,:at is ! diff]5ce betwe5 an amp]e & a c\lomb8 ,ans4 ,an amp]e is ! unit rate ( fl[ ( ! curr5t1 & a c\lomb is ! unit quantity ( electricity1 t is1 ! amp]e is ! rate ( curr5t fl[ t w deposit 4#jjjcbhf grammes ( copp] 9 "o second & a c\lomb is ! quantity ( electricity t passes a giv5 po9t 9 "o second :5 ! curr5t /r5g? is "o amp]e4 ,9 o!r words a c\lomb is "o amp]e second4 ,illu/ration3 ,fig4 #ede4--;,gas voltamet] = det]m9+ ! /r5g? ( curr5t by ! volume ( gas evolv$4 ,to use1 connect up z %[n 9 ! illu/ration4 ,adju/ s t ! z]o position ( ! burette is ab\t "o-half in* bel[ ! level ( ! top ( ! ,u tube4 ,p\r acidulat$ wat] into ! m\? ( ! burette till ! wat] 9 ! ,u tube is ab\t "o-half in* f ! top4 ,) ! electrodes ins]t$ ?r\gh ! corks1 c>efully place ea* "o 9 position by giv+ a slight twi/ to ! "r z ! cork ent]s4 ,! wat] level 9 ! ,u tube & burette %\ld n[ be ! same1 or fur!r adju/m5t mu/ be made to atta9 ?is result4 ,! level 9 ! burette does n necess>ily h to correspond ) ! z]o graduation1 b mu/ n be bel[ x4 ,unclamp ! burette & hold x ne>ly horizontal4 ,! liquid w n run out if ! corks be tight1 s t ?is is ! air leakage te/4 ,atta* ! connectors & wires f ! curr5t s\rce 7:i* %\ld h a pressure ( #b or m volts7 plac+ a swit* 9 ! circuit4 ,:5 ! swit* is clos$1 bubbles ( gas w rise 9 ! ,u tube f bo? electrodes1 displac+ ! wat] & =c+ x up ! burette4 ,hydrog5 w be lib]at$ ov] ! negative electrode1 & oxyg5 ov] ! positive electrode 9 ! proportion ( twice z mu* hydrog5 z oxyg54 ,to calculate ! curr5t /r5g?1 divide ! volume ( gas lib]at$ by ! "t 9 seconds1 & by ! volume ( gas lib]at$ 79 cubic c5timet]s7 by "o amp]e 9 "o second & by 4#agcc2 t is3 amp]es volume ( gas lib]at$ 7"t 9 seconds 4#agcc74 ,,example4--,if an arc lamp require a curr5t ( #h amp]es1 h[ mu* electricity does x consume p] h\r8 ,s9ce "o c\lomb "o amp]e second1 ! quantity ( electricity consum$ p] h\r is #h amp]es 7 #fj #fj 7 #bh1hjj c\lombs4 ,voltamet]4--,a voltamet] is an electrolytic cell employ$ to measure an electric curr5t by ! am\nt ( *emical decomposition ! curr5t causes 9 pass+ ?r\gh ! cell4 ,!re are two classes ( voltamet]3 #a4 ,weight voltamet]s2 #b4 ,gas voltamet]s4 ,ques4 ,:at is ! diff]5ce betwe5 ^! two classes ( voltamet]8 ,ans4 ,9 "o1 ! curr5t /r5g? is det]m9$ by ! weight ( metal deposit$ or weight ( wat] decompos$1 & 9 ! o!r by ! volume ( gas lib]at$4 ,fig4 #edd %[s a weight voltamet] & fig4 #ede a gas voltamet]4 ,ques4 ,h[ %\ld ! plates ( a weight voltamet] be treat$ be=e use8 ,ans4 ,!y mu/ be ?or\ghly clean$ & poli%$ ) s&pap]1 ! s& be+ aft]w>ds remov$ by plac+ !m 9 runn+ wat]4 ,! f+]s mu/ n be plac$ on any "p ( ! plate :i* is to receive ! deposit4 ,ques4 ,:at =m ( voltamet] has be5 select$ to measure ! ,int]national amp]e8 ,ans4 ,! silv] voltamet] arrang$ z "h specifi$3 ,! ca?ode on :i* ! silv] is to be deposit$ %all take ! =m ( a plat9um b[l1 n less ?an #aj cms4 9 diamet]1 & f #d to #e cms4 9 dep?4 ,! anode %all be a disc or plate ( pure silv] "s #cj sq4 cms4 9 area1 & #b or #c cms4 9 ?ickness4 ,?is %all be support$ horizontally 9 ! liquid ne> ! top ( ! solution by a silv] rod rivet$ ?r\gh its c5t]4 ,to prev5t ! dis9tegrat$ silv] :i* is =m$ on ! anode fall+ ^u ! ca?ode1 ! anode %all be wrapp$ ar\nd ) pure filt] pap]1 secur$ at ! back by suitable fold+4 ,! liquid %all consi/ ( a neutral solution ( pure silv] nitrate conta9+ ab\t #ae p>ts by weight ( ! nitrate to #he p>ts ( wat]4 ,ques4 ,:at is ! value ( ! ,int]national amp]e z measur$ ) ! silv] voltamet]8 ,ans4 ,! ,int]national amp]e is repres5t$ suffici5tly well = practical use by ! unv>y+ curr5t :i*1 :5 pass$ ?r\gh a silv] voltamet] 7z describ$ above7 deposits silv] at ! rate ( 4#jjaaah gramme p] second4 ,illu/ration3 ,fig4 #edf4--,s+le contact & %ort circuit+ key4 ,?is key is int5d$ especially = use ) ,d',arsonval galvanomet]s 9 z]o deflection me?ods4 ,! key is connect$ 9 circuit ) ! galvanomet] s t :5ev] ! key is n depress$1 ! galvanomet] is %ort circuit$1 & its oscillations quickly damp$ out by ! curr5ts induc$ 9 its coil4 ,! back end ( ! spr+ is held 9 a slot 9 a rubb] block atta*$ to ! base4 ,ohm's ,law & ! ,ohm4--,! v>i\s te/s "h describ$ dep5d = _! tru? ^u ! def9ite relation exi/+ betwe5 ! electric curr5t1 its pressure1 & ! resi/ance :i* ! circuit (f]s to its fl[4 ,?is relation 0 fully inve/igat$ by ,ohm 9 #ahbg4 ,us+ ! same conductor1 he prov$ n only t ! curr5t v>ies ) ! pressure1 b t x v>ies 9 direct proportion4 ,ohm's law has already be5 discuss$ 9 a previ\s *apt] & ! sev]al ways ( express+ x are repeat$ "h = conv5i5ce3 volts #a4 ,amp]es -------2 ohms #b4 ,volts amp]es ohms2 volts #c4 ,ohms ---------4 amp]es ,v>i\s values h be5 assign$1 f "t to "t1 to ! ohm or unit ( resi/ance1 ! unit 9 use at ! pres5t "t be+ kn[n z ! ,int]national ohm4 ,?is 0 recomm5d$ at ! meet+ ( ! ,briti% ,association 9 #ahib1 0 adopt$ by ! ,int]national ,electrical ,congress held 9 ,*icago 9 #ahic1 & 0 legaliz$ = use 9 ! ,unit$ ,/ates by act ( ,congress 9 #ahid4 ,! ,int]national ohm 9 graphically def9$ 9 fig4 #edh4 ,! previ\s values giv5 to ! ohm :i* 7 m or less g5]ally accept$ are z foll[s3 ,! ,siem5s' ,ohm4--,a resi/ance due to a column ( m]cury #ajj cm4 long & #a sq4 mm4 9 cross section at #j ,c4 ,b4 ,a4 7,briti% ,association7 ,ohm4--,a resi/ance due to a column ( m]cury approximately #ajd4i cm4 long & #a sq4 mm4 9 cross section at #j ,c4 ,legal ,ohm4--,a resi/ance due to a column ( m]cury #ajf cm4 long & #a sq4 mm4 9 cross section at #j ,c4 ,?is unit 0 adopt$ by ! ,p>is conf]5ce ( #ahhd4 ,,ohm ,,table,a ,int]- ,date national ,legal,b4 ,a4 ,siem5s' ,ohm ,ohm,ohm ,ohm ---------------------------------------- ----------------------- ,int]national ,ohm #ahic-d #a4jjjj #a4jjbh #a4jacf #a4jfcj ,legal ,ohm #ahhd 4#iigb #a4jjjj #a4jajg #a4jfjj ,b4 ,a4 ,ohm #ahfd 4#ihff 4#ihid #a4jjjj #a4jdhh ,siem5s' ,ohm 4#idjg 4#idcd 4#iece #a4jjjj ,a ,,note4--,9 ! above table to r$uce1 = in/ance1 ,briti% ,association ohms to ,int]national ohms1 multiply by 4#ihff1 or divide by #a4jacf2 to r$uce legal ohms to ,int]national ohms1 multiply by 4#iigb1 or divide by #a4jjbh1 etc4 ,illu/ration3 ,fig4 #edg4--;,d\ble contact key4 ,x is ( especial value 9 connection ) a ,:eat/one bridge4 ,:5 us$ ) ! latt] x =ms a comb9ation batt]y & galvanomet] key4 ,! batt]y is wir$ to ! top leaves ( ! key & ! galvanomet] to ! l[] leaves4 ,h5ce1 :5 op]at$1 ! batt]y circuit w be clos$ be=e ! galvanomet] circuit1 z x is desirable to avoid undue di/urbance ( ! ne$le4 ,illu/ration3 ,fig4 #edh4--,! int]national ohm4 ,x is def9$ z ! resi/ance ( #ad4deb grammes ( m]cury 9 ! =m ( a column ( uni=m cross section #ajf4c c5timet]s 9 l5g?1 at a temp]ature ( #j ,c4 ,?is is approximately equival5t to a column #ajf4c cm4 long1 hav+ a uni=m cross section ( #a sq4 mm4 ,9 ! figure ! int]national ohm is def9$ graphically4 ,! resi/ance ( ! ext]nal circuit & ! /&>d "o volt cell is assum$ to be z]o4 ,illu/ration3 ,fig4 #edi4--,le$s & ,nor?rup "o ohm /&>d resi/ance 7,rei*san/alt =m72 adju/$ at #bj ,c4 ,l[ resi/ance /&>ds may be prop]ly divid$ into two classes3 #a4 ^? :i* are design$ prim>ily z resi/ance /&>ds1 & #b4 ^? design$ z curr5t c>ry+ /&>ds4 ,^? ( ! fir/ m5tion$ class are (t5 us$ to measure curr5ts up to _! capacity4 ,! above /&>d has bo? pressure & curr5t t]m9als4 ,! b9d+ po/s = ! =m] are m\nt$ on high po/s s z to be easily accessible :5 ! /&>d is imm]s$ 9 oil4 ,:5 us$ z a resi/ance /&>d ( precision1 x %\ld n be subject$ to a curr5t ( m ?an "o amp]e1 & :5 us$ z a curr5t c>ry+ /&>d ( less] accuracy1 a curr5t ( #b or #c amp]es may be us$4 ,practical ,/&>ds ( ,resi/ance4--,! column ( m]cury z %[n 9 fig4 #edh1 is ! recogniz$ /&>d = resi/ance1 h[ev]1 9 practice1 x is n conv5i5t to comp>e resi/ances ) su* a piece ( app>atus1 & !re=e second>y /&>ds are made up & /&>diz$ ) a great degree ( precision4 ,^! second>y /&>ds are made ( wire4 ,! mat]ial g5]ally us$ be+ mangan9 or plat9oid4 ,illu/ration3 ,fig4 #eej4--;,direct deflection me?od ( te/+ resi/ances2 a useful & simple me?od :i* may be us$ 9 num]\s te/s4 ,galvanomet] read+s are tak5 ?r\gh ! kn[n1 & unkn[n resi/ances1 & ! curr5t be+ proportional to ! deflections1 ! value ( ! unkn[n resi/ance is easily calculat$4 ,resi/ance ,measurem5t4--,resi/ance is t :i* (f]s opposition to ! fl[ ( electricity4 ,ohm's law %[s t ! /r5g? ( ! curr5t falls (f 9 proportion z ! resi/ance 9 ! circuit increases4 ,?is gives a basis = measur+ resi/ance4 ,!re are v>i\s me?ods by :i* an unkn[n resi/ance may be measur$1 z by !3 #a4 ,direct deflection me?od2 #b4 ,me?od ( sub/itution2 #c4 ,fall ( pot5tial me?od2 #d4 ,diff]5tial galvanomet] me?od2 #e4 ,drop me?od2 #f4 ,voltmet] me?od2 #g4 ,:eat/one bridge me?od4 ,direct ,deflection ,me?od4--,?is me?od is bas$ on ! fact t ! great] ! curr5t ?r\gh a galvanomet] ! great] ! deflection ( ! ne$le2 x is a simple me?od & is capable ( ext5d$ application4 ,! app>atus requir$ consi/s ( batt]y1 galvanomet]1 kn[n resi/ance1 & d\ble contact key4 ,! connections are made z 9 fig4 #eej4 ,! kn[n resi/ance is put 9 circuit ) ! galvanomet] & aft] not+ ! deflection1 ! key is mov$ s z to cut out ! kn[n resi/ance & ?r[ into circuit ! unkn[n resi/ance4 ,! deflection ( ! galvanomet] is aga9 not$ & comp>$ ) ! fir/ deflection4 ,illu/ration3 ,fig4 #eea4--;,*>ge & dis*>ge key1 adapt$ to cond5s] te/+ :]e ! cond5s] is to be alt]nately *>g$ & dis*>g$4 ,! insulat$ h&le enables ! key to be us$ )\t insulat+ ! body4 ,illu/ration3 ,fig4 #eeb4--,pohl commutator4 ,?is is equival5t to a two pole d\ble ?r[ swit*4 ,! depressions 9 ! base are fill$ ) m]cury into :i* ! contacts dip 9 clos+ ! circuit4 ,if ! deflections be proportional to ! curr5t1 ! unkn[n resi/ance w be z _m times ! kn[n resi/ance z ! deflection ) ! kn[n resi/ance is great] ?an ! deflection ) ! unkn[n resi/ance4 ,me?od ( ,sub/itution4--,?is is ! simple/ me?od ( measur+ resi/ance4 ,! resi/ance to be measur$ is ins]t$ 9 s]ies ) a galvanomet] & "s con/ant s\rce ( curr5t1 & ! galvanomet] deflection not$4 ,a kn[n adju/able resi/ance is !n sub/itut$ = ! unkn[n & adju/$ till ! same deflection is aga9 obta9$4 ,! value ( ! adju/able resi/ance ?us obta9$ is equal to t ( ! resi/ance be+ te/$4 ,illu/ration3 ,fig4 #eec4--,sub/itution me?od ( te/+ resi/ances4 ,! connections & app>atus are ! same z 9 fig4 #eej1 except t a resi/ance box is us$ 9 place ( ! kn[n resi/ance4 ,9 mak+ ! te/1 fir/ note deflection ) unkn[n resi/ance 9 circuit1 !n press key s t ! curr5t w pass ?r\gh ! resi/ance box1 & adju/ ! resi/ance 9 ! box s t ! deflection ( ! galvanomet] is ab\t ! same z ) ! unkn[n4 ,n[ swit* f "o circuit to ! o!r1 *ang+ ! resi/ance 9 ! box until equal deflections are obta9$4 ,:5 ?is obta9s1 ! resi/ance 9 ! box is ! same z ! resi/ance be+ te/$4 ,ques4 ,:at k9d ( adju/able resi/ance is us$ 9 mak+ ! above te/8 ,ans4 ,a resi/ance box4 ,ques4 ,describe a resi/ance box4 ,ans4 ,x consi/s ( a box conta9+ num]\s resi/ance coils ) _! ends connect$ to t]m9als & provid$ ) plugs s t !y may be ?r[n into or out ( circuit at w1 ?us v>y+ ! resi/ance 9 ! circuit4 ,illu/ration3 ,fig4 #eed4--,ord9>y resi/ance box4 ,x conta9s sets ( /&>d resi/ances consi/+ ( coils ( insulat$ wire hav+ l[ conductivity & small temp]ature coeffici5t4 ,! ends ( ! coils are jo9$ to ! section ( ! b> betwe5 ! plugs4 ,! ins]tion ( a plug cuts out a coil4 ,9 us+1 c>e %\ld be tak5 to put ! plugs 9 ) a slight twi/ s t !re %all be no resi/ance introduc$ by poor contact4 ,fall ( ,pot5tial ,me?od4--,?is is a v simple me?od ( measur+ resi/ances1 & "o t is conv5i5t = practical "w 9 electrical /ations because x requires only an ammet]1 voltmet]1 batt]y & swit*--app>atus to be f\nd 9 e /ation4 ,! connections are made z %[n 9 fig4 #eee4 ,9 mak+ ! te/ ! ammet] & voltmet] read+s are tak5 at ! same "t1 & ! unkn[n resi/ance calculat$ f ,ohm's law4 ,accord+ly1 s9ce3 7#a7 amp]es volts _/ ohms solv+ = ! resi/ance1 7#b7 ohms volts _/ amp]es ,illu/ration3 ,fig4 #eee4--;,fall ( pot5tial me?od ( te/+ resi/ances2 a conv5i5t me?od = te/+ at /ations1 requir+ only ! usual in/rum5ts to be f\nd at a /ation4 ,! resi/ance ( ! voltmet] mu/ be v high1 o!rwise ! te/ mu/ be made z 9 fig4 #eef4 ,,example4--,if 9 fig4 #eee ! read+s %[ #f volts & #b amp]es h[ _m ohms is ! resi/ance be+ te/$8 ,sub/itut+ 9 =mula 7#b7 ohms #f_/b #c ,ques4 ,c ?is te/ be made ) any k9d ( voltmet]8 ,ans4 ,its resi/ance mu/ be v high to avoid error4 ,:5 a voltmet] hav+ small resi/ance is us$1 x %\ld be connect$ s z to measure ! fall ( pressure across bo? ammet] & unkn[n resi/ance z %[n 9 fig4 #eef4 ,illu/ration3 ,fig4 #eef4--;,fall ( pot5tial me?od ( te/+ resi/ances2 diagram %[+ connections = te/+ ) l[ resi/ance voltmet]4 ,! resi/ance measur$ ) ?is connection w be ! sum ( ! resi/ances ( ! coil & ! ammet]4 ,! resi/ance ( ! ammet] is usually kn[n & c be subtract$ f ! sum to obta9 ! requir$ resi/ance4 ,diff]5tial ,galvanomet] ,me?od4--,?is is :at is kn[n z a nil or z]o me?od1 t is1 a me?od ( mak+ electrical measurem5ts 9 :i* comp>ison is made betwe5 two quantities by r$uc+ "o to equality ) ! o!r1 ! abs5ce ( deflection f z]o ( ! in/rum5t scale %[+ t ! equality has be5 obta9$4 ,! te/ is made ) a diff]5tial galvanomet]1 & resi/ance box connect$ z 9 fig4 #eeg4 ,! curr5t !n w divide s t "p ( x fl[s ?r\gh ! resi/ance be+ te/$ & ar\nd "o set ( coils ( ! galvanomet] :ile ! o!r "p w fl[ ?r\gh ! resi/ance box & ! o!r set ( coils z indicat$4 ,:5 ! resi/ance box has be5 s adju/$ t its resi/ance is ! same z ! unkn[n resi/ance ! curr5t 9 ! two bran*es w be equal1 & ! ne$le ( ! galvanomet] w %[ no deflection4 ,illu/ration3 ,fig4 #eeg4--;,diff]5tial galvanomet] me?od ( te/+ resi/ances4 ,9 mak+ ! te/1 ! resi/ance box is adju/$ till ! galvanomet] ne$le %[s no deflection4 ,:5 ?is condition obta9s1 ! resi/ance 9 circuit 9 ! resi/ance box is equal to ! unkn[n resi/ance1 h5ce1 a read+ ( ! box gives ! value ( ! unkn[n resi/ance4 ,ques4 ,:at "n is giv5 to ?is me?od ( te/+8 ,ans4 ,x is call$ a z]o me?od1 di/+ui%+ x f deflection me?ods4 ,ques4 ,= :at k9d ( resi/ance is ! me?od adapt$8 ,ans4 ,s9ce x is a nil or z]o me?od1 x is bett] adapt$ to ! measurem5t ( non-inductive ?an ( inductive resi/ances4 ,ques4 ,:at precaution %\ld be tak5 ) inductive resi/ances8 ,ans4 ,! curr5t mu/ be all[$ to fl[ until x becomes /eady to ov]come ! influ5ce ( self-induction4 ,ques4 ,:at may be said ) respect to ! diff]5tial galvanomet] me?od8 ,ans4 ,) an accurate in/rum5t x is v reliable4 ,illu/ration3 ,fig4 #eeh4--;,drop me?od ( te/+ resi/ances4 ,! app>atus is connect$ z %[n & read+s tak5 ) voltmet] across kn[n & unkn[n resi/ance4 ,! unkn[n resi/ance is !n easily calculat$4 ,drop ,me?od4--,?is is a conv5i5t me?od1 & "o :i* may be us$ = measur+ ei!r high or l[ resi/ances ) precision4 ,x is us$ = _m practical measurem5ts1 & requires only a voltmet]1 batt]y1 kn[n resi/ance & a two way swit*4 ,! in/rum5ts are connect$ z 9 fig4 #eeh1 & 9 mak+ ! te/1 ! voltmet] is swit*$ into circuit across ! kn[n resi/ance & !n across ! unkn[n resi/ance1 read+s be+ tak5 9 ea* case4 ,! value ( ! unkn[n resi/ance1 is !n easily calculat$ f ! foll[+ proportion3 drop across kn[n resi/ance kn[n resi/ance ------------------------------ ------------------ drop across unkn[n resi/ance unkn[n resi/ance f :i* unkn[n kn[n resi/ance drop across unkn[n resi/ance resi/ance ---------------------------------------- ----------------- drop across kn[n resi/ance ,illu/ration3 ,fig4 #eei4--,le$s & ,nor?rup portable galvanomet] 7po9t] type ,a74 ,! s5sitiv5ess ( ?is in/rum5t is su* t x may be sub/itut$ 9 num]\s cases = ! non-portable reflect+ type ( galvanomet]2 z = in/ance1 9 ! *eck+ ( ammet]s & voltmet]s to an accuracy ( 4#b by ! pot5tiomet] me?od1 & on almo/ all ,:eat/one bridge measurem5ts to comm]cial accuracies4 ,a curr5t ( #b micro-amp]es w cause ! po9t] to move #a mm4 ov] ! scale1 t is1 x has a s5sibility ( #ejj1jjj ohms4 ,! me?od ( susp5d+ ! mov+ sy/em is su* z to practically elim9ate initial friction :i* is ( value 9 all z]o deflect+ me?ods4 ,! susp5sions & mov+ sy/em are gu>d$ by spr+s1 :i* toge!r ) ! solid con/ruction ( ! case r5d] ! in/rum5t capable ( )/&+ r\gh usage4 ,ov]all dim5sions are #e-a_/d #b-e_/h #c-a_/b2 weight ab\t #c p\nds4 ,ques4 ,:at may be sub/itut$ = ! voltmet]8 ,ans4 ,a high resi/ance galvanomet]1 ^: deflections are proportional to ! curr5t1 ! value ( ! deflections be+ sub/itut$ 9 ! =mula4 ,ques4 ,:at precaution %\ld be tak5 9 mak+ ! te/8 ,ans4 ,! curr5t us$ %\ld n be /rong en\gh to appreciably heat ! resi/ance1 & if ! curr5t be n v /eady1 sev]al read+s %\ld be tak5 ( ea* measurem5t & ! av]age values us$ 9 ! =mula4 ,ques4 ,h[ are ! mo/ accurate results obta9$8 ,ans4 ,by select+ ! kn[n resi/ance z ne> z possible to ! suppos$ value ( ! unkn[n resi/ance4 ,illu/ration3 ,fig4 #efj4--,voltmet] me?od ( te/+ resi/ances4 ,kn[+ ! resi/ance ( ! voltmet]1 turn swit* to ! left & f read+ calculate resi/ance correspond+ to "o division ( ! scale4 ,turn swit* to "r & multiply read+ by resi/ance requir$ = deflection ( "o division4 ,?is gives resi/ance ( voltmet] & unkn[n resi/ance2 subtract+ f ?is ! resi/ance ( voltmet] gives value ( ! unkn[n resi/ance4 ,voltmet] ,me?od4--,?is is a direct deflection me?od & consi/s 9 det]m9+ fir/ ! resi/ance t w deflect ! ne$le ?r\gh "o division ( ! scale on a giv5 batt]y curr5t1 !n ) ?is z a basis = comp>ison ! voltmet] is connect$ across ! unkn[n resi/ance ^: value is easily calculat$ f ! read+4 ,9 mak+ ! te/1 ! in/rum5ts are connect$ z 9 fig4 #efj4 ,! curr5t f batt]y is fir/ pass$ ?r\gh ! galvanomet] by turn+ swit* z %[n4 ,illu/ration3 ,fig4 #efa4--,megohm box or set ( /&>d high resi/ances4 ,! box conta9s five resi/ances ( #bjj1jjj ohms ea*4 ,! six pill>s are petticoat insulat$1 ! resi/ances be+ plac$ betwe5 ea* pair ( pill>s4 ,!re is a d\ble contact po/ on top ( ea* pill> s t ^! c be connect$ toge!r ) copp] l9ks4 ,assum+ t ! resi/ance ( ! in/rum5t is #h1jjj ohms & t ! curr5t deflects ! ne$le ?r\gh #aj divisions ( ! scale1 !n = a deflection ( "o division ! resi/ance is #h1jjj #aj #hj1jjj ohms4 ,accord+ly1 if1 :5 ! swit* is mov$ to ! "r1 connect+ ! voltmet] across ! unkn[n resi/ance1 ! ne$le be mov$ ?r\gh #f divisions ( ! scale1 ! comb9$ resi/ance ( ! voltmet] & unkn[n resi/ance is #hj1jjj #f #ac1ccc-a_/c ohms1 & subtract+ ! resi/ance ( ! voltmet]1 ! value ( ! unkn[n resi/ance is #ac1ccc-a_/c - #h1jjj #e1ccc-a_/c ohms4 ,ques4 ,= :at k9ds ( te/ is ! voltmet] me?od be/ adapt$8 ,ans4 ,= measur+ high resi/ances1 z ! insulation ( wires1 etc4 ,ques4 ,:at may be said ) respect to ! curr5t us$8 ,ans4 ,its voltage %\ld be z high z possible )9 ! limits ( ! voltmet] scale4 ,illu/ration3 ,fig4 #efc4--,/&>d resi/ance box3 #ajj1jjj ohms1 9 f\r units ( #aj1jjj1 #bj1jjj1 #cj1jjj1 & #dj1jjj ohms4 ,an inf9ity plug sep>ates ea* coil f ! ones adjac5t4 ,segm5ts are elevat$ f ! h>d rubb] top by special wa%]s 9 ord] to increase insulation4 ,b9d+ po/s are s arrang$ z n to be 9 ! way :5 plugs are us$4 ,illu/ration3 ,fig4 #efb4--,/&>d high resi/ance box3 #ajj1jjj ohms4 ,x is m\nt$ 9 a brass box ) a h>d rubb] top4 ,connections %\ld be made to t]m9als m>k$ #c & #d4 ,:5 ! flexible cord is on plug #a1 ! box is %ort circuit$1 b :5 on plug #b1 ! resi/ance ( #ajj1jjj ohms is 9 s]ies4 ,! box is especially suit$ to rapid cable te/+4 ,ques4 ,9 te/+ cable insulation :at is desirable ) respect to voltmet] & curr5t8 ,ans4 ,a l[ read+ voltmet] %\ld be us$ 9 connection ) a l>ge batt]y4 ,illu/ration3 ,fig4 #efd4--;,diagram %[+ pr9ciple ( ,:eat/one's bridge4 ,a1 ,b1 ,c1 & ,d1 are ! f\r memb]s :i* con/itute ! bridge4 ,! curr5t f ! batt]y divides at ,p1 "p trav]s+ ,,dc1 & "p trav]s+ ,,ba4 ,! galvanomet] connect$ to ,m & ,n w indicate :5 ! curr5ts are equal 9 ! two bran*es by giv+ no deflection4 ,?is is !n a z]o or nil me?od ( te/+4 ,! resi/ances & keys requir$ 9 te/+ are %[n 9 fig4 #efe4 ,9 ! actual in/rum5t1 ! memb]s ,a1 ,b1 ,c1 & ,d are kn[n by ! names giv5 9 ! figure4 ,:eat/one ,bridge ,me?od4--,= accurate measurem5ts ( resi/ance ?is me?od is almo/ univ]sally us$4 ,! s-call$ ,:eat/one bridge 0 inv5t$ by ,*ri/ie1 & improp]ly cr$it$ to ,:eat/one1 :o simply appli$ ,*ri/ie's inv5tion to ! measurem5t ( resi/ances4 ,illu/ration3 ,fig4 #efe4--;,diagram %[+ arms ( ,:eat/one bridge1 resi/ances & me?od ( connect+ galvanomet]1 batt]y & unkn[n resi/ance4 ,! bridge consi/s ( a sy/em ( conductors z %[n 9 fig4 #efd4 ,! circuit ( a con/ant batt]y is made to bran* at ,p into two p>ts1 :i* re-unite at ,q1 s t "p ( ! curr5t fl[s ?r\gh ! po9t ,m1 ! o!r "p ?r\gh ! po9t ,n4 ,! f\r conductors ,a1 ,b1 ,c1 ,d1 are spok5 ( z ! arms ( ! balance or bridge4 ,x is by ! proportion exi/+ betwe5 ! resi/ances ( ^! arms t ! resi/ance ( "o ( !m c be calculat$ :5 ! resi/ances ( ! o!r ?ree are kn[n4 ,:5 ! curr5t :i* />ts f ! batt]y arrives at ,p1 ! pressure w h fall5 to a c]ta9 value4 ,! pressure 9 ! upp] bran* falls aga9 to ,m1 & cont9ues to fall to ,q4 ,! pressure ( ! l[] bran* falls to ,n1 & aga9 falls till x rea*es ! value at ,q4 ,n[ if ,n be ! same proportionate di/ance along ! resi/ances betwe5 ,p & ,q1 z ,m is along ! resi/ances ( ! upp] l9e betwe5 ,p & ,q1 ! pressure w h fall5 at ,n to ! same value z x has fall5 to at ,m2 or1 9 o!r words1 if ! ratio ( ! resi/ance ,c to ! resi/ance ,d be equal to ! ratio betwe5 ! resi/ance ,a & ! resi/ance ,b1 !n ,m & ,n w be at equal pressures4 ,to f9d out if ?is condition obta91 a s5sitive galvanomet] is plac$ 9 a bran* wire betwe5 ,m & ,n :i* w %[ no deflection :5 ,m & ,n are at equal pressure or :5 ! f\r resi/ances ( ! arms balance "o ano!r by be+ 9 proportion1 ?us3 7#a7 ,a3,c ,b3,d ,if1 !n1 ! value ( ,a1 ,b1 & ,c be kn[n1 ,d c be calculat$4 ,! proportion 7#a7 is r$uc$ to ! foll[+ equation be=e sub/itut+4 ,d ,,bc_/,a ,= in/ance1 if ,a & ,c be1 z 9 fig4 #efe1 #aj ohms & #ajj ohms respectively1 & ,b be #ae ohms1 ,d w be 7#ae #ajj7 #aj #aej ohms4 ,illu/ration3 ,fig4 #eff4--;,diagram %[+ usual arrangem5t ( resi/ances 9 arms ( ,:eat/one's bridge4 ,9 practice ! bridge is seldom or nev] made 9 ! loz5ge %ape ( ! diagrams1 figs4 #efd & #efe1 ^! be+ giv5 m]ely = cle>ness4 ,! resi/ance box ( fig4 #eed is1 9 itself1 a complete bridge1 ! appropriate connections be+ made by screws at v>i\s po9ts4 ,! lett]s 9 ! above diagram correspond ) ^? 9 figs4 #efd & #efe1 & ! ?ree figures %\ld be c>efully comp>$4 ,z con/ruct$1 ,:eat/one bridges are provid$ ) "s resi/ance coils 9 ! arms ,a & ,c1 z well z ) a complete set 9 ! arm ,b4 ,! advantage ( ?is arrangem5t is t by adju/+ ,a & ,c1 ! proportionality betwe5 ,b & ,d c be det]m9$1 & c1 9 c]ta9 cases1 be measur$ to fractions ( an ohm4 ,9 fig4 #efe resi/ances ( #aj1 #ajj1 & #a1jjj ohms are includ$ 9 ! arms ,a & ,c4 ,illu/ration3 ,fig4 #efg4--,/&>d resi/ance box & ,:eat/one bridge4 ,?is patt]n is a modification ( ! ,an?ony =m ( bridge4 ,all ! resi/ances are w\nd ^u metal spools4 ,! bridge ratio coils are #a1 #aj1 #ajj1 #a1jjj1 #aj1jjj4 ,! rheo/at coils are arrang$ 9 five r[s1 ( t5 coils ea*4 ,! ord9>y decade plan 7expla9$ 9 fig4 #egj7 is foll[$4 ,! coils may be jo9$ 9 s]ies 9 multiple1 or 9 any comb9ation ( s]ies & multiple4 ,! coils may ?us be *eck$ aga9/ ea* o!r 9 _m comb9ations4 ,= in/ance1 all ! t5 ohm coils tak5 9 p>allel may be comp>$ ) any "o ohm coil4 ,! precision ( adju/m5t is said to be #a_/bj? ( #a = ! coils ( ! t5? ohm s]ies1 & #a_/ej? ( #a = ! coils ( ! rheo/at4 ,! ratio coils are c]tifi$ to be l ea* o!r to )9 #a_/ajj? ( #a4 ,! box is suppli$ ) batt]y & galvanomet] keys ( sub/antial con/ruction4 ,ques4 ,describe ! me?od ( te/+ ) ! bridge4 ,ans4 ,fig4 #efg illu/rates ! g5]al arrangem5t ( resi/ances to be f\nd 9 an ord9>y bridge4 ,! connections are made z %[n4 ,9 te/+1 fir/ depress ! batt]y key1 !n tap ! galvanomet] key4 ,?is %\ld be repeat$ adju/+ ! resi/ances till no deflection is obta9$4 ,! resi/ance !n 9 ! arm ,b 7,c ,a7 w give ! value ( ! unkn[n resi/ance4 ,illu/ration3 ,fig4 #efh4--,ratio coils ( ,:eat/one bridge4 ,almo/ e box int5d$ to s]ve z a ,:eat/one bridge is furni%$ ) a set ( coils :i* =ms ! arms ( proportion or ratio arms ( ! bridge4 ,!re is a *oice ( sev]al diff]5t ways ( arrang+ ^! coils4 ,! figure %[s ! simple/ arrangem5t1 :i* is employ$ 9 boxes n int5d$ = ! highe/ accuracy4 ,! requir$ ratio1 z = in/ance #a3ajj1 is obta9$ by )draw+ a plug f ea* arm ,a & ,b4 ,ratios #a_/a1 #a_/aj1 #a_/ajj1 #aj_/ajj1 etc41 or #a1jjj_/a1 #a1jjj_/aj1 #a1jjj_/ajj1 #ajj_/ajj1 etc41 are obta9able 9 ?is mann]4 ,?is simple arrangem5t is op5 n only to ! objection t ! contact resi/ance ( ! plugs :i* rema9 9 is always includ$ ) ! resi/ance unplugg$1 b also to all o!r objections to be urg$ aga9/ ! use ( _m plugs :]e a few w d4 ,! me?od has ! limitation t x is n possible to rev]se ! arms ( ! bridge1 t is1 to transpose ! arms ,a & ,b4 ,ques4 ,:y %\ld ! batt]y key be depress$ be=e ! galvanomet] key8 ,ans4 ,to avoid ! sudd5 sw+ ( ! galvanomet] ne$le1 :i* occurs on clos+ circuit 9 consequ5ce ( self-induction4 ,ques4 ,h[ is x kn[n :e!r too mu* or too little resi/ance be unplugg$8 ,ans4 ,! galvanomet] ne$le w be deflect$ to "o side = too mu* resi/ance1 & to ! opposite side = too little resi/ance4 ,illu/ration3 ,fig4 #efi4--,me?od ( rev]s+ arms ( ,:eat/one bridge ) rev]s+ blocks4 ,! arrangem5t %[n 9 ! figure is classical1 be+ t us$ 9 ! ,engli% po/ (fice type ( ,:eat/one bridge4 ,x is op5 to ! objections :i* apply to ! use ( sev]al plugs1 "o ( :i* is )drawn to obta9 ! desir$ resi/ance4 ,ques4 ,:at is ! mean+ ( ,inf41 m>k$ on ! bridge8 ,ans4 ,x /&s = inf9ity1 because ! resi/ance coil at ! po9t m>k$ inf9ity is omitt$ s t adjac5t sections ( ! arm are disconnect$ :5 ! plug is tak5 out4 ,9 fact1 ! air gap int]pos$ by ! removal ( ! plug by no means provides an inf9itely great resi/ance1 b is usually call$ su* because x is va/ly great] ?an any ( ! o!r resi/ances ( ! bridge4 ,illu/ration3 ,fig4 #egj4 ,illu/ration3 ,figs4 #egj & #ega4--;,diagrams illu/rat+ ! decade plan ( comb9+ resi/ance coils4 ,9 ?is me?od ! coils are connect$ 9 s]ies & ! arrangem5t avoids ! disadvantage ( ! ord9>y ,:eat/one bridge 9 t ! latt] requires a l>ge numb] ( plugs to %ort circuit ! resi/ances n 9 use1 :i* introduces an elem5t ( unc]ta9ty z to resi/ance ( ! plug contacts & ! necessity ( add+ up ! values ( all ! unplugg$ resi/ances 9 ord] to det]m9e ! total resi/ance 9 circuit4 ,! necess>y regul> succession ( values 9 a rheo/at built on ! decade plan c be obta9$ ) ei!r n9e or t5 coils p] decade4 ,! *ief reason = us+ ! latt] numb] is f\nd 9 ! facility ) :i* all ! coils ( "o decade c be comp>$ ) "o coil ( ! next high] decade1 ?us p]mitt+ ! coils ( a rheo/at to be *eck$ among !mselves4 ,?us1 ! t5 #a ohm coils c be *eck$ ) a #aj ohm1 ! t5 #aj's ) a #ajj1 etc4 ,9 "s sets ! t5 coils ( a decade c be connect$ 9 s]ies or 9 p>allel1 & x !n becomes an advantage to h t5 coils to a decade1 s9ce ! coils 9 "o decade 9 p>allel equal "o ( ! coils ( ! next l[] decade4 ,:5 ^! latt] advantages are n requir$1 & especially :5 dials or slid+ swit*es are us$1 !re is little or no advantage 9 us+ m ?an n9e coils p] decade1 z %[n 9 fig4 #egj4 ,"h all ! coils ( ! set are connect$ 9 s]ies s t ! circuit is nev] op54 ,?us x is a slight advantage to h p]man5t connections a1 b1 & c1 because all ! coils ( a decade c be ?r[n 9 circuit by simply pull+ out a plug1 x n be+ necess>y to ins]t x aga91 z w\ld be ! case if ! a1 b1 & c connections 7 n us$4 ,moreov]1 if any plug make bad contact1 its effect is some:at less5$ by hav+ ?is bad contact %unt$ by ! rema9+ coils ( ! decade4 ,aga91 !re are occasions :]e viol5t deflections ( a galvanomet] are prev5t$ by n hav+ ! circuit entirely op5 :5 a plug is tak5 out4 ,! ,decade ,plan4--,9 ?is me?od ( comb9+ resi/ance coils1 !re are #i or #aj "o ohm coils = ! units place1 #i or #aj t5 ohm coils = ! t5s place1 #i or #aj "o hundr$ ohm coils = ! hundr$s place & s on4 ,ea* s]ies ( coils ( ! same value is designat$ a decade4 ,! connections are usually made z %[n 9 figs4 #egj & #ega4 ,x is app>5t f ! figure t any value 9 any "o decade c be obta9$ by ins]t+ betwe5 a b> & a block1 only "o plug2 moreov] if sev]al decades be 9 s]ies1 any value up to ! limit ( ! set c be read (f directly f ! position ( ! plugs )\t hav+ to add up ! unplugg$ resi/ance z 9 ! ord9>y arrangem5t4 ,illu/ration3 ,fig4 #egb4--,two plug arrangem5t ( ratio coils4 ,ea* ( ! ratio coils has "o ( its t]m9als connect$ to a common c5t] :i* corresponds to ! block m>k$ ,c 9 ! figure4 ,! o!r t]m9al ( ea* coil is connect$ to an individual block1 !re be+ "o block = ea* coil4 ,! b> ,b on "o side ( ^! blocks is jo9$ to ! rheo/at & ! b> ,a on ! o!r side to an ,x po/4 ,9 ! ord9>y use ( ?is set ( ratio coils two plugs only are us$4 ,"o plug is ins]t$ betwe5 ! b> ,a & "o ( ! blocks1 #a1 #a'1 #aj1 #aj'1 etc41 ( ! c5tral r[ ( blocks4 ,! o!r plug is ins]t$ betwe5 ! b> ,b & any "o ( ! o!r blocks ( ! c5tral r[4 ,!re are two ratio coils ( ea* value4 ,to obta9 an ev5 ratio z #a1jjj to #a1jjj'1 "o plug is ins]t$ betwe5 ! block #a1jjj & ! b> ,a1 & ! o!r plug betwe5 ! #a1jjj block & b> ,b1 ! ratio arms are rev]s$2 t is1 ! #a1jjj ohm coil is connect$ to ! ,x po/ & ! #a1jjj ohm coil to ! end ( ! rheo/at4 ,:5 unev5 ratios are us$1 ! same ratio c be obta9$ by f\r diff]5t comb9ations4 ,to obta9 ! ratio "o to t51 ins]t a plug betwe5 ,a & #a1 & ano!r betwe5 ,b & #aj1 or betwe5 ,a & #a'1 & ,b & #aj1 & get #a3aj1 or betwe5 ,a & #a1 & ,b & #aj'1 & get #a3aj'1 or aga91 betwe5 ,a & #a' & ,b & #aj'1 & get #a' to #aj'4 ,o!r ratios are obta9$ 9 a simil> mann]4 ,by us+ m ?an two plugs & connect+ c]ta9 ( ! coils 9 p>allel comb9ations1 a l>ge numb] ( o!r ratios may be obta9$4 ,?is arrangem5t (f]s a conv5i5t me?od ( measur+ ! s5sibility ( a bridge & galvanomet] comb9ation t is frequ5tly applicable4 ,if = in/ance ! "o ohm coil is us$ on ei!r side aft] a balance has be5 obta9$ ! "o ohm may be %unt$ ) ! #a1jjj ohm on ! same side4 ,?is w make a v>iation ( #a_/aj ( #a & ! galvanomet] deflection may be not$ = ?is v>iation4 ,simil>ly1 ! #a ohm may be %unt$ ) ! #ajj = a v>iation ( #a1 or ) ! #aj1jjj = a v>iation ( #a_/ajj ( #a4 ,! t5 ohm coil may be %unt$ ) ! #a1jjj = a v>iation ( #a & ) ! #aj1jjj = a v>iation ( #a_/aj ( #a4 ,9 ! arrangem5t ( ratio coils1 errors due to plug contacts are negligible because only two plug contacts ent] ! circuit1 & ) an ev5 ratio1 x is only ! diff]5ce 9 ! resi/ances ( ! two plug contacts t c affect ! result4 ,9 measur+ any ( ! ratio coils :ile 9 ! box x is only necess>y to connect to ! b> ,c & to ei!r ! b> ,a or ,b & plug 9 ! coils to be measur$4 ,illu/ration3 ,fig4 #egc4 ,illu/ration3 ,figs4 #egc & #egd4--,! ,le$s & ,nor?rup decade4 ,! object ( ?is arrangem5t is to r$uce ! numb] ( coils requir$4 ,9 fig4 #egc1 ! #a1 #c'1 #c & #b are connect$ 9 s]ies4 ,let ! t]m9als ( ! #a ohm & #b ohm coils be numb]$ 7#a71 7#b71 7#c71 7#d7 & 7#e7 7fig4 #egc74 ,! curr5t ent]s at po9t 7#a7 & leaves ! coils at ! po9t 7#e71 trav]s+ #a1 #c'1 #c1 #b #i ohms 9 all4 ,if ?is s]ies be multipli$ by any factor n1 !n n 7#a #c' #c #b7 n #i ohms4 ,x w be se5 t if ! po9ts 7#a7 & 7#e7 be connect$1 all ! coils are %ort circuit$1 & ! curr5t w trav]se z]o resi/ance4 ,if ! po9ts 7#b7 & 7#e7 be connect$1 ! #c'1 #c & #b ohm coils w be %ort circuit$ & ! curr5t w trav]se #a ohm4 ,by ext5d+ ! process s z to connect two & only two po9ts at a "t x is possible to obta9 ! regul> succession ( values n 7#j1 #a1 #b1 #c1 #d1 #e1 #f1 #g1 #h1 #i71 ! la/ be+ obta9$ :5 no po9ts are connect$4 ,fig4 #egd %[s ,le$s & ,nor?rup's me?od ( connect+ ^! po9ts two at a "t ) ! use ( a s+le plug4 ,! circles 9 ! diagram repres5t two r[s ( t5 brass blocks ea*4 ,to ! fir/ two blocks at ! top ( ! r[s1 ! po9ts 7#e7 & 7#a71 fig4 #egc1 are connect$2 to ! second two1 ! po9ts 7#b7 & 7#e7 are connect$1 etc41 no po9ts be+ connect$ to ! la/ pair ( blocks4 ,h5ce1 if a plug be ins]t$ betwe5 blocks #a & #e1 fig4 #ege1 ! po9ts 7#a7 & 7#e7 ( diagram fig4 #egc are connect$1 giv+ ! value ( #j1 if betwe5 ! blocks #b & #e ! po9ts 7#b7 & 7#e7 are connect$1 giv+ ! value #a1 & s on4 ,! value #i is obta9able :5 ! plug is 9 ! la/ pair ( blocks1 :i* h no connections4 ,fig4 #egb %[s a top view ( ! blocks ( a simple decade con/ruct$ ^u ?is plan4 ,ques4 ,:at o!r advantages are ga9$ ) ! decade arrangem5t8 ,ans4 ,! s+le plug us$ ) ea* decade is nev] out ( use1 be+ ei!r 9 ! z]o position or set on "s value1 & is !re=e n easily lo/ by be+ laid aside4 ,! use ( only "o plug 9 a decade makes x easy to asc]ta9 t ! plug is mak+ good contact z only "o block 9 a r[ is plugg$ at a "t1 ! o!r blocks are n kept "u a /ra9 by hav+ plugs =c$ tightly betwe5 !m4 ,?is /ra9 on ! blocks1 :i* always exi/s 9 ^? sets 9 :i* a resi/ance is ?r[n 9 by remov+ a plug1 t5ds to sep>ate or loos5 !m & (t5 to w>p ! h>d rubb] ^u :i* !y are m\nt$4 ,ano!r advantage ( ! decade plan is t x p]mits obta9+ a succession ( values by means ( slid+ contacts or dial swit*es1 a me?od :i* is becom+ des]v$ly m appreciat$4 ,illu/ration3 ,fig4 #ege4--,le$s & ,nor?rup dial ,:eat/one bridge4 ,rotat+ swit*es are us$ in/ead ( plugs1 :i* p]mits quick] adju/m5t ( ! resi/ances1 adapt+ x to rapid work+4 ,! ratio coils are arrang$ z 9 fig4 #efh4 ,!re are f\r dials :i* =m ! rheo/at4 ,! units dial conta9s #i "o ohm coils2 ! t5s dial1 #i t5 ohm coils2 ! hundr$s dial1 #i "o hundr$ ohm coils1 & ! ?\s&s dial #i "o ?\s& ohm coils4 ,! values ( ! ratio coils are #a1 #a1 #aj1 #aj1 #ajj1 #ajj1 #a1jjj1 #a1jjj1 #aj1jjj1 #aj1jjj4 ,ques4 ,:at is ! diff]5ce betwe5 plug out & plug 9 types ( resi/ance box8 ,ans4 ,9 ! plug out type1 resi/ance is put 9 ! circuit by remov+ plugs1 z 9 fig4 #efe2 9 ! plug 9 type1 resi/ance is put 9 ! circuit by ins]t+ plugs z 9 figs4 #egj & #ega4 ,illu/ration3 ,fig4 #egf4--,que5 ,acme portable te/+ set4 ,x consi/s ( a ,:eat/one bridge1 ) rev]sible arms1 batt]y ( f\r dry cells1 ,d',arsonval galvanomet]1 batt]y & galvanomet] keys4 ,!re are sixte5 resi/ance coils1 hav+ a comb9$ resi/ance ( #aa1aaj ohms4 ,ea* bridge arm is provid$ ) ?ree coils ( #a1 #aj1 #ajj ohms1 & #aj1 #ajj1 #a1jjj ohms respectively4 ,! commutator admits ( a ratio ( #a to #a1jjj on ei!r bridge arm1 giv+ ! set a !oretical range f 4#jja ( an ohm to #aa1aaj1jjj ohms4 ,= resi/ances above #a1jjj1jjj ohms1 ! normal batt]y p[] mu/ be increas$4 ,! contact keys are locat$ z %[n4 ,! batt]y key has s+le contact1 b ! galvanomet] key has d\ble contact2 depress+ x closes ! galvanomet] circuit1 & releas+ x %ort circuits ! galvanomet]1 br++ ! latt] quickly to re/4 ,te/+ ,sets4--,= conv5i5ce 9 te/+1 a comb9ation ( ! in/rum5ts us$ is put up 9 a neat & sub/antial case1 & kn[n z a te/+ set4 ,!re are innum]able =ms ( te/+ set1 a few ( :i* are %[n 9 ! accompany+ illu/rations4 ,! usual comb9ation is a ,:eat/one bridge1 galvanomet]1 batt]y & necess>y keys & connections4 ,illu/ration3 ,fig4 #egg4--;,connections & circuits ( ,que5 acme portable te/+ set4 ,!re are ?ree r[s ( blocks1 ,,ll'1 ,,mm'1 ,,nn'4 ,,ll is connect$ to ,,nn' by means ( a heavy copp] b>1 jo9+ ,l' & ,n'4 ,,ll' & ,,nn' con/itute ! rheo/at1 f :i* any resi/ance f #a ohm to #aa1aaj ohms may be obta9$ by remov+ ! prop] plugs4 ,! block ,n ( ! rheo/at is connect$ to ! l[] l9e po/ ,d4 ,! upp] l9e po/ ,c is connect$ to ! block ,x ( ! commutator4 ,! block ,c has no o!r p]man5t connection1 except key ,g4 ,! block ,r ( ! commutator is connect$ to ! block ,l ( ! rheo/at1 & has no o!r connection1 except+ by plugs4 ,ea* half ( ,,mm' con/itutes a bridge arm1 designat$ ,a & ,b respectively4 ,beg9n+ at ! l[] l9e po/ ,d1 ! connections =m a cont9u\s circuit ?r\gh ! rheo/at1 !nce ?r\gh ! bridge arm ,b1 !nce ?r\gh ! bridge arm ,a1 !nce to ! upp] l9e po/ ,c4 ,! commutator s]ves m]ely to rev]se ! bridge arms ,a & ,b4 ,! batt]y t]m9als are connect$ z %[n3 ! positive t]m9al directly to ! common junction ( ! two bridge arms1 & ! negative t]m9al ?r\gh ! batt]y key to ! rheo/at4 ,! positive t]m9al ( ! galvanomet] is connect$ ?r\gh ! galvanomet] key ) ! block ,x1 & ! negative t]m9al ) ! block ,r ( ! commutator or :at is equival5t1 ) ! block ,l ( ! rheo/at4 ,! commutator blocks ,a1 ,b1 ,r & ,x1 are connect$ by plugs z %[n4 ,:5 ! commutator plugs are 9 ! position ,,pq1 ! bridge arm ,b is connect$ to ! rheo/at & ! bridge arm ,a is connect$ to ! l9e1 ! ratio betwe5 ! bridge arms ratio be+ ,a ,b ,x ,r b :5 ! plugs are 9 ! position ,,/1 ! bridge arms are rev]s$ 9 position ,a1 be+ connect$ ) ! rheo/at & ,b1 ) ! l9e1 & ! bridge arm ratio becomes ,a ,b ,r ,x4 ,! connections ( ! te/+ set may be m readily und]/ood f ! simplifi$ diagram fig4 #egh4 ,illu/ration3 ,fig4 #egh4--,simplifi$ diagram %[+ connections ( ,que5 ,acme portable te/+ set4 ,ques4 ,describe ! op]ation ( ! ,que5 ,acme te/+ set figs4 #egf & #egg1 9 measur+ resi/ance4 ,ans4 ,connect ! t]m9als ( ! resi/ance to be measur$ to ! l9e po/s ,c & ,d4 ,place ! batt]y connections on ! two upp] tips #j & #a1 ?us ?r[+ "o end ( ! batt]y into circuit1 :i* is suffici5t until an approximate balance is obta9$4 ,employ ! #ajj ohm coil 9 ea* bridge arm1 & place ! commutator plugs 9 ! position ,,pq1 or 9 ! position ,,/4 ,!n remove plugs f ! rheo/at until ! value ( total resi/ance employ$1 or ne>ly z may be guess$ is equal to t ( ! unkn[n resi/ance4 ,n[ press ! batt]y key ,ba1 & hold+ x d[n mom5t>ily1 press ! galvanomet] key ,ga4 ,if ! galvanomet] ne$le sw+ to ! "r t[>d ! symbol ! resi/ance employ$ 9 ! rheo/at is too high & mu/ be r$uc$4 ,if ! ne$le sw+ to ! left t[>d -1 ! resi/ance employ$ is too l[ & mu/ be increas$4 ,by alt]+ ! resi/ance ( ! rheo/at accord+ly1 a value w soon be f\nd1 :i* :5 v>i$ slightly ei!r way1 w rev]se ! deflection ( ! galvanomet] ne$le4 ,n[ remove ! batt]y connection f tip #a1 & place x on ! tip #d1 ?us ?r[+ ! :ole batt]y into circuit4 ,!n press ! keys aga9 z be=e1 fir/ ! batt]y key1 !n ! galvanomet] key4 ,?is w increase ! deflection ( ! galvanomet] ne$le = ! same v>iation 9 ! rheo/at1 ?us enabl+ ! mak+ ( a m accurate adju/m5t4 ,! measurem5t ?us made w be ! be/ result t c be obta9$ ) bridge arms ( equal value1 b by select+ m suitable values ( ! two arms f ! foll[+ table ( bridge ratios a mu* high] degree ( accuracy may be obta9$4 ,illu/ration3 ,fig4 #egi4--;,diagram ( ! ,que5 dial decade portable te/+ set4 ,its dim5sions are #i-a_/b long1 #g wide & #g deep1 & weighs #aa-a_/b p\nds4 ,! resi/ances are arrang$ ^u ! dial decade plan1 be+ plac$ 9 circuit by means ( a rotat+ swit* contact4 ,! swit*es are s con/ruct$ t !y may be turn$ 9 ei!r direction1 !reby p]mitt+ !m to be turn$ quickly f ! highe/ resi/ance 9 any dial to ! l[e/ resi/ance 9 ! same dial4 ,?is arrangem5t avoids ! necessity ( turn+ back ?r\gh all ! rema9+ resi/ances 9 any p>ticul> gr\p ( coils & is ( value 9 locat+ sw++ crosses or conditions ( mom5t>y balances4 ,! connections = ! v>i\s te/s are made by ! manipulation ( "o small knife swit* 7,w4,b4--,m4,l47 & ! swit* ,,ba42 ^! are pla9ly lett]$1 ?us avoid+ ! necessity ( ref]r+ to a diagram ( connections4 ,9 con/ruction1 ! dial swit*es are made up ( eight lam9ations ( ,no4 #bh ,b4 ,s4 phosphor bronze1 & ! =m is su* z to prev5t we>+ grooves on ! top ( ! contact /uds4 ,9 ?is in/rum5t ! electrical circuits are sold]$ ?r\gh\t except+ ! swit* contact ^: resi/ance is negligible4 ,! resi/ances are w\nd ) mangan94 ,! batt]y comprises six cells sub-divid$ :i* are easily replaceable4 ,! galvanomet] is ! same z 9 ! ,que5 acme set1 b has ! addition ( an ,ayrton %unt1 :i* is useful 9 mak+ insulation measurem5ts4 ,! necess>y keys1 b9d+ po/s1 & swit*es are provid$ s z to facilitate ! use ( ! in/rum5t = ! v>i\s measurem5ts t c be made ) x4 ,table ,%[+ ! ,be/ ,values ( ,bridge ,arms = ,measur+ any ,desir$ ,resi/ance ,position ( ,be/ ,values ( ,commutator ,plugs z ,value ( ,resi/ance be+ measur$ %[n 9 ,a ,b fig4 #ehb ---------------------------------------- ------------------------ ,bel[ #a4e ohms #a #a1jjj ,,pq ,betwe5 #a4e & #aa ohms #a #ajj ,,pq #aa & #gh ohms #aj #ajj ,,pq #gh & #a1ajj ohms #ajj #a1jjj ,,pq #a1ajj & #f1ajj ohms #ajj #ajj ,,pq or ,,/ #f1ajj & #aaj1jjj ohms #a1jjj #ajj ,,/ #aaj1jjj & #a1aaj1jjj ohms #a1jjj #aj ,,/ #a1aaj1jjj & #aa1aaj1jjj ohms #a1jjj #a ,,/ ,ques4 ,9 te/+ ) ! ,que5 ,acme set h[ %\ld ! plugs be plac$ 9 ! commutator8 ,ans4 ,always make ! arm ,a ! small] except :5 ! two arms are ( equal value4 ,ques4 ,if ! resi/ance be+ measur$ is high] ?an #f1ajj ohms1 or l[] ?an #a1ajj ohms1 h[ %\ld ! commutator plugs be plac$8 ,ans4 ,if high] ?an #f1ajj ohms1 !y %\ld be plac$ 9 ! position ,,/2 if l[] ?an #a1ajj ohms1 9 position ,,pq4 ,:5 ! plugs are plac$ 9 ! ,,/ position1 ! unkn[n resi/ance is f\nd by divid+ ! value ( ! l>g] bridge arm by t ( ! small]1 & multiply+ ! total employ$ resi/ance 9 ! rheo/at by ! quoti5t4 ,:5 ! plugs are plac$ 9 ! ,,pq position1 ! employ$ resi/ance 9 ! rheo/at is divid$ by ! quoti5t4 ,illu/ration3 ,fig4 #ehj4--,que5 portable silv] *loride te/+ batt]y4 ,! silv] *loride cell has ! advantage ( long life1 light weight1 & compactness4 ,! pressure ( ea* cell :5 new is 4#h volt4 ,direct ,deflection ,me?od ) ,que5 ,acme ,set4--,to measure = in/ance1 insulation resi/ance by direct deflection connect a kn[n high resi/ance1 say #ajj1jjj ohms betwe5 ! l9e po/ ,c 7fig4 #egg71 & ! positive batt]y po/4 ,remove all plugs f ! commutator1 & place all plugs 9 ! rheo/at1 z any employ$ resi/ance 9 ! rheo/at w be 9 circuit ) ! galvanomet] & ! batt]y4 ,place ! batt]y connection s z to ?r[ only "o cell into circuit4 ,n[ press ! keys & obta9 a deflection ( ! galvanomet] ne$le4 ,= example3 assume t ! ne$le to be deflect$ ab\t #h divisions ( ! scale4 ,s9ce ?is deflection is due to ! curr5t f "o cell pass+ ?r\gh a resi/ance ( #ajj1jjj ohms1 !n #ajj1jjj #h 4#h megohms repres5ts ! resi/ance ?r\gh :i* "o cell w produce a deflection ( "o division on ! scale4 ,h5ce1 4#h megohms is ! con/ant ( ! galvanomet]4 ,illu/ration3 ,fig4 #eha4--,ohmmet]4 ,x consi/s ess5tially ( a slide wire ,:eat/one bridge1 ) ! scale divid$ to read ei!r directly 9 ohms1 or 9 p] c5t4 ( a fix$ resi/ance value4 ,a galvanomet] is m\nt$ on ! conta9+ case ( ea*1 & batt]y & galvanomet] keys are provid$4 ,9 ! direct read+ type1 ! scale is s cut t :5 ! galvanomet] is balanc$1 ! po9t] ( ! in/rum5t indicates ! value ( ! resi/ance betwe5 ! ,x po/s4 ,! scale is calibrat$ = any desir$ range4 ,^! ohmmet]s be+ slide wire bridges1 ! greate/ accuracy is at ! c5t] ( ! scale1 h5ce "o %\ld be select$ t w br+ ! "p ( ! scale likely to be ! mo/ us$ at or ne> ! c5t]4 ,a conv5i5t type is t 9 :i* ! scale is cut 9 p] c5t41 #ajj p] c5t4 be+ at ! c5t] ( ! scale4 ,fix$ coils ( #a1 #aj1 #ajj1 #a1jjj & #aj1jjj ohms are conta9$ 9 ! in/rum5t ) a plugg+ arrangem5t all[+ any "o to be us$4 ,:5 a balance is obta9$1 ! actual resi/ance is det]m9$ by multiply+ ! dial read+ by ! value ( ! fix$ coil 9 use4 ,?is am\nts simply to %ift+ ! decimal po9t4 ,= in/ance1 if ! #ajj ohm coil 7 be+ us$1 & ! po9t] 7 at 4#hge1 ! resi/ance w\ld be #hg4e ohms4 ,n[1 replace ! kn[n high resi/ance 7#ajj1jjj ohms7 by ! unkn[n resi/ance 7= in/ance su* z a cable7 ! value ( :i* is to be det]m9$4 ,add en\gh cells to produce z l>ge a deflection ( ! ne$le z possible4 ,assume t #ge cells give a deflection ( #a4e scale division4 ,!n1 ! galvanomet] con/ant multipli$ by ! numb] ( cells & ! product divid$ by ! deflection w give ! insulation resi/ance ( ! cable2 or #j4h megohm #ge cells #fj4j2 & #fj4j #a4e #dj megohms z ! resi/ance ( ! cable4 ,illu/ration3 ,fig4 #ehb4--;,commutator plug sett+ = comp>+ electromotive =ces by ! fall ( pot5tial me?od ) ,que5 acme set4 ,fall ( ,pot5tial ,me?od ) ,que5 ,acme ,set4--,to comp>e electromotive =ces by ?is me?od1 place ! batt]y connection 7fig4 #egg71 s z to ?r[ into circuit all ! cells1 tak+ c>e n to rev]se !m by cross+ ! batt]y cords4 ,plug ! commutator z %[n 9 fig4 #ehb1 & remove #a1jjj ohms f bridge arm ,b4 ,place all plugs 9 arm ,a4 ,f ! rheo/at unplug #e1jjj ohms4 ,!n connect "o ( ! cells be+ te/$1 ) its positive t]m9al to ! batt]y po/ & its negative t]m9al to ! l9e po/ ,c4 ,:5 ! keys are press$1 ! galvanomet] ne$le w sw+ ei!r to ! "r or to ! left4 ,if x sw+ t[>d 1 r$uce ! resi/ance 9 ! rheo/at2 if x sw+ t[>d -1 add resi/ance to ! rheo/at4 ,:5 a value is f\nd :]e9 a v>iation ( an ohm ei!r way rev]ses ! deflection1 add to ?is value ! resi/ance unplugg$ 9 arm ,b1 & divide ! sum by ! resi/ance 9 arm ,b4 ,! result gives ! ratio betwe5 ! voltages ( ! te/+ set batt]y & cell be+ te/$ respectively4 ,! division is decimal & may be readily accompli%$ by m]ely po9t+ (f z _m places z !re are ciph]s 9 ! resi/ance employ$ f arm ,b4 ,?is op]ation repeat$ ) any numb] ( diff]5t cells1 w give _! voltages 9 t]ms ( ! voltage ( ! te/+ set batt]y1 & f ^! ratios _! relative values may be readily obta9$4 ,illu/ration3 ,fig4 #ehc4--;,diagram ( app>atus = measur+ l[ resi/ances bas$ on ! pr9ciple ( ! ,kelv9 d\ble bridge4 ,9 ! diagram ,,ab repres5ts a heavy piece ( resi/ance metal ( uni=m cross section & uni=m resi/ance p] unit ( l5g?2 ,,cd is ano!r piece ( resi/ance metal ( small] cross section1 & ! two are jo9$ toge!r by a heavy copp] b>1 ,,ac1 into :i* bo? are silv] sold]$2 ,,ll are ! curr5t t]m9als & ,,pp are ! pressure t]m9als4 ,! resi/ance ( ,,ab betwe5 ! m>ks #j & #ajj on ! scale ,s is 4#jja ohm4 ,f ! po9t #a on ! resi/ance ,,cd to #j on ,,ab is also 4#jja ohm1 f #b to #j is 4#jjb & s on1 & f #i to #ajj is 4#ja ohm4 ,! slid] ,m moves along ! resi/ance ,,ab & its position is read on ! scale ,s :i* is divid$ into #ajj equal p>ts & c be read by a v]ni] to ?\s&?s4 ,subdivid$ 9 ?is way ! resi/ance betwe5 ! tap (f po9ts ,,pp may h any value f 4#jja to 4#ja ohms by /eps ( 4#jjjjja ohm4 ,if ! te/+ set batt]y be replac$ by a /&>d cell1 ! fir/ measurem5t gives at once ! voltage ( ! cell te/$4 ,if ! voltage ( ! cell or batt]y be+ te/$ exce$ t ( ! te/+ set batt]y1 rev]se ! position ( ! two batt]ies1 & ! subsequ5t op]ations1 z outl9$ above1 w give ! desir$ results4 ,h[ to *eck a ,voltmet] ) ! ,que5 ,acme ,set4--,9 us+ a set z 9 fig4 #egf1 fir/ remove ab\t #aj1jjj ohms f ! rheo/at1 plug ! commutator z %[n 9 fig4 #ehb1 remove #ajj ohms f ! arm ,b1 ( ! bridge1 & connect a /&>d cell ) ! positive t]m9al to ! batt]y po/ & ! negative t]m9al to ! l9e po/ ,c4 ,!n1 connect ! circuit to ! batt]y po/s ( ! te/+ set ! positive lead to ! po/ & ! negative lead to ! - po/4 ,n[1 press bo? keys & note ! direction ( ! deflection ( ! galvanomet] ne$le4 ,if x move t[>d 1 ! rheo/at resi/ance is too high2 if t[>d -1 too l[4 ,illu/ration3 ,fig4 #ehd4--,kelv9 bridge4 ,?is includes a l[ resi/ance /&>d ( 4#a ohm v>iable by /eps ( 4#jjjja ohm1 a set ( ratio coils1 & a hold] = rods or wires to be measur$1 ) a scale to measure _! l5g?4 ,x is also provid$ ) heavy flexibles to be us$ 9 measur+ ! resi/ances ( irregul>ly %ap$ pieces4 ,! connections are cle>ly %[n 9 ! diagram4 ,! range ( measurem5ts ( ?is bridge is3 #a ohm to 4#a ohm by /eps ( 4#jja ohm readily e/imat$ to 4#jjja2 4#a to 4#ja ohm by /eps ( 4#jjja ohm readily e/imat$ to 4#jjjja2 4#ja ohm to 4#jja ohm by /eps ( 4#jjjja ohm1 readily e/imat$ to 4#jjjjja2 4#jja ohm d[n by /eps ( 4#jjjja ohm1 readily e/imat$ to 4#jjjjja ohm4 ,*ange ! rheo/at resi/ance accord+ly until ! balance atta9$ is su* t a v slight v>iation ( ! rheo/at resi/ance "o way or ! o!r w rev]se ! galvanomet] deflection4 ,to f9d ! pressure on ! circuit1 add #ajj to rheo/at resi/ance & po9t (f two places4 ,multiply ?is value by ! voltage & ! product w be ! desir$ voltage4 ,if ! voltage ( ! /&>d cell be exactly "o volt1 ! total employ$ resi/ance repres5ts ! voltage on ! circuit4 ,illu/ration3 ,fig4 #ehe4--,que5 slide wire bridge4 ,x consi/s ( a portable slide wire1 ,:eat/one bridge arrang$ to read directly 9 ohms 9 addition to its use = locat+ crosses & gr\nds4 ,x is complete ) batt]y1 galvanomet] & telephone receiv]4 ,! bridge is balanc$ by mov+ ! h& /ylus until ! galvanomet] %[s no deflection or until !re is no s\nd 9 ! telephone receiv]4 ,9 ord] to provide a wide range ( measurem5t & maximum accuracy1 ratio coils or multipli]s hav+ values ( #a1 #aj1 #ajj1 #a1jjj & #aj1jjj are provid$4 ,! scale ( ! in/rum5t is arrang$ 9 two p>ts1 "o ( :i* indicates ohms & ! o!r is divid$ into uni=m divisions = use :5 locat+ crosses & gr\nds by ! ,murray & ,v>ley loop me?ods4 ,a small induction coil is includ$ s z to furni% an alt]nat+ curr5t :5 us+ ! telephone receiv]4 ,= in/ance1 9 mak+ a measurem5t on a #aaj volt circuit1 assume t ! employ+ ( #g1hdj ohms rheo/at resi/ance produces balance1 & t increas+ or decreas+ ?is resi/ance by two ohms1 rev]ses ! galvanomet] deflection4 ,?is indication t ! sett+ #g1hdj is unc]ta91 ab\t #a_/dj ( #a p] c5t4 ,s9ce ! rheo/at coils are adju/$ to an accuracy ( only #a_/e ( #a p] c5t41 t w be ab\t ! accuracy ( ! measurem5t4 ,if ! pressure ( ! /&>d cell be #a4jah volts1 !n #g1hdj #ajj #g1idj4 ,po9t+ (f two places1 gives #gi4dj1 :i* multipli$ by #a4jah gives #hj4hb = ! voltage on ! circuit4 ,to ,measure ,int]nal ,resi/ance ( ,cell ) ,que5 ,acme ,set4--,fir/ comp>e its voltage on op5 circuit ) ! pressure ( ! te/+ set batt]y4 ,!n1 %unt ! cell ) a kn[n resi/ance1 ab\t #ajj ohms1 & aga9 measure its t]m9al voltage4 ,! diff]5ce betwe5 ! two values ?us obta9$1 divid$ by ! value ( ! %unt resi/ance1 w give ! value ( ! curr5t4 ,to f9d ! int]nal resi/ance1 multiply ! value ( ! %unt resi/ance by ! ratio betwe5 ! fir/ & second measur$ values4 ,illu/ration3 ,fig4 #ehf4--;,ev]%$ portable ohmmet] set4 ,?is te/+ set consi/s ( a direct read+ ohmmet] :i* indicates by direct read+ ! value ( ! resi/ance be+ te/$1 also a portable h& dynamo :i* provides at any requir$ pressure ! curr5t necess>y to make ! te/4 ,x is adapt$ to ! ne$s ( supply /ations1 wir+ contractors & dynamo build]s4 ,x is also useful 9 te/+ ! insulation ( und]gr\nd & a]ial cables1 & is design$ s t x c be us$ by ord9>y workm5 :o are n exp]i5c$ 9 h&l+ delicate in/rum5ts & :o1 by its use1 are able to obta9 accurate results4 ,! dynamo is w\nd = #ajj1 #bjj1 #ejj1 or #a1jjj volts1 & is fitt$ ) spr+ drum inside ! case on :i* is coil$ a tw9 flexible cord provid$ ) a connector adapt$ = clamp+ "u ! ohmmet] t]m9als4 ,= in/ance1 assume t ! op5 circuit voltage ( ! cell be+ te/$ z comp>$ ) ! voltage ( ! te/+ set batt]y is 4#bab ( ! latt]1 & t :5 x is %unt$ ) a resi/ance ( #a1jjj ohms1 its t]m9al voltage is 4#agi4 ,!n1 ! total resi/ance is to ! #a1jjj ohms %unt resi/ance z 4#bab is to 4#agi or 74#bab_/4agi7 #a1jjj #a1ahd1 f :i* d$uct+ ! #a1jjj ohms %unt resi/ance1 gives #ahd ohms z ! int]nal resi/ance ( ! cell4 ,illu/ration3 ,fig4 #ehg4--,le$s & ,nor?rup fault f9d]4 ,a l9eman's in/rum5t = ! location ( faults1 crosses1 gr\nds1 & op5s 9 telephone & telegraph circuits1 & = ! measurem5t ( conductor & insulation resi/ance4 ,illu/ration3 ,fig4 #ehh4--;,diagram %[+ arrangem5t & connections ( ,le$s & ,nor?rup fault f9d]4 ,x is us$ to measure conductor resi/ance1 fault resi/ance1 to locate faults by f\r diff]5t te/s1 & :5 us$ ) a buzz] & telephone1 to locate op5s4 ,! ess5tial feature ( ! in/rum5t is ! uni=m resi/ance ,,ab1 :i* lies 9 a circle & :i* has a value ( ab\t #ajj ohms4 ,by a special con/ruction1 x is s arrang$ t ! contact c be made at any po9t along x1 & x is !re=e equival5t to a v high resi/ance slide wire4 ,x has a mov+ contact ,c & a uni=m scale ( #a1jjj divisions4 ,9 s]ies ) ?is1 !re are ! two resi/ances ,e & ,r :i* may be %ort circuit$ by ! swit*es ,u & ,v4 ,e has exactly ! same resi/ance z ! wire ,,ab4 ,r has a resi/ance ( #ajj ohms1 & is ! fix$ resi/ance ( ! bridge arrangem5t = resi/ance measurem5ts4 ,! resi/ances ( #a1jjj ohms & #i1jjj ohms connect$ to ! batt]y po/ are to protect ! batt]y & ! app>atus f excessive curr5t4 ,! #i1jjj ohms may be %ort circuit$ by ! swit* ,w4 ,ammet] ,te/ ) ,que5 ,acme ,set4--,connect a l[ resi/ance 9 s]ies ) ! ammet] & run leads f x to ! te/+ set1 ! positive lead to ! batt]y po/ & ! negative lead to ! l9e po/ ,c 7fig4 #egg74 ,ins]t a /&>d cell betwe5 ! batt]y po/s1 ) positive t]m9al to batt]y po/1 & negative t]m9al to - batt]y po/4 ,plug commutator z %[n 9 fig4 #ehb4 ,remove #aj1jjj ohms f rheo/at1 & #ajj ohms f bridge arm ,b4 ,det]m9e a balance 9 ! usual way by *ang+ ! value ( ! resi/ance 9 ! rheo/at4 ,?is op]ation w balance ! diff]5ce ( pressure at ! t]m9als ( ! %unt resi/ance aga9/ ! /&>d cell1 & its value is equal to 7#a4dj #ajj7 _/ 7,r #ajj7 #adj _/ 7,r #ajj7 ,to det]m9e ! curr5t fl[+1 divide ! value ( ! diff]5ce ( pressure ?us obta9$ by ! value ( ! %unt resi/ance4 ,illu/ration3 ,fig4 #ehi4--,resi/ance measurem5t ) ,le$s & ,nor?rup fault f9d]4 ,! diagram %[s ! prop] connections & swit* sett+s = measur+ conductor resi/ance4 ,z 9 ! ord9>y slide wire bridge1 ! resi/ance ,x betwe5 ! two po/s #a & #b is obta9$ f ! =mula ,x ,a 7#a1jjj - ,a7 ,r4 ,to avoid ! necessity ( solv+ 9 ea* case ! fraction ,a 7#a1jjj - ,a71 a table is furni%$ ) ! in/rum5t1 giv+ ! value ( ?is fraction = ea* value ( ,a4 ,! resi/ance is accord+ly det]m9$ 9 ea* case by simply sett+ ! contact ,c = a balance & read+ f ! table ! resi/ance opposite ! numb] correspond+ to ! scale read+ & multiply+ by #ajj1 ! value ( ,r4 ,to use an outside batt]y1 remove ! inside batt]y & connect ! outside batt]y betwe5 ! po/s ,gr & ,ba4 ,! pressure ( ?is batt]y %\ld n exce$ #aaj volts4 ,if x exce$ #be volts1 op5 swit* ,w4 ,,example--,) an unkn[n resi/ance connect$ betwe5 ! po/s #a & #b1 ! galvanomet] %[$ a balance = a dial read+ ( #chg4 ,! numb] opposite #chg 9 ! table is 4#fcac2 h5ce1 ,x 4#fcac #ajj #fc4ac ohms4 ,illu/ration3 ,fig4 #eij4--;,diagram ( ! ,que5 /&>d pot5tiomet]4 ,! circuit arrangem5t is a me?od ( sub-divid+ ! ma9 pot5tiomet] wire1 ,,mnopq1 s z to provide = v accurate read+4 ,! second>y voltage1 or t us$ to supply curr5t to ! ma9 pot5tiomet] circuit1 is adju/$ by regulat+ rheo/ats1 ,fa/1 ,m$ium1 & ,sl[ s t ! curr5t fl[ is exactly 4#jjja amp]e4 ,x is not$ t ?is in/rum5t requires a v small curr5t = its op]ation4 ,! in/rum5t is direct read+ = voltage measurem5ts1 n exce$+ #a4d4 ,9 ord] to det]m9e if ! curr5t fl[ ?r\gh ! pot5tiomet] be exactly 4#jjja amp]e1 ! t]m9als ( ! /&>d cell b9d+ po/s are connect$ 9 circuit s t ! drop ov] po9ts betwe5 :i* !y are connect$ are exactly equal to ! voltage ( ! /&>d cell us$4 ,b9d+ po/s are provid$ = connection ) v>i\s /&>d cells4 ,! unkn[n voltage to be measur$ is plac$ 9 opposition to ! curr5t fl[ 9 ! pot5tiomet] circuit by connect+ to ! b9d+ po/ ,,xemf4 ,obs]ve t pol>ity is connect$ z requir$4 ,! galvanomet] ) its %unt is plac$ 9 ! /&>d cell circuit1 or ,x circuit1 by means ( a d\ble pole1 d\ble ?r[ swit*4 ,! swit* at ,t provides = /&>d cells ( diff]5t values & ! sett+ at ,u all[s = temp]ature correction4 ,! range ( ! in/rum5t 9 volts c be increas$ by means ( multipli]s or volt boxes4 ,illu/ration3 ,fig4 #eia4 ,illu/ration3 ,fig4 #eib4 ,illu/ration3 ,fig4 #eic4 ,illu/ration3 ,figs4 #eia to #eid4--;,diagrams illu/rat+ loop te/+4 ,to prop]ly und]/& ! ,murray or ,v>ley loop te/s1 consid] a ,:eat/one bridge 7fig4 #eia7 ! arms ( :i* are equal4 ,9 loop te/+1 ! rheo/at is replac$ by a l5g? ( cable & ! unkn[n resi/ance also by a l5g? ( cable1 z 9 fig4 #eib1 bo? be+ simil> 9 resi/ance p] foot4 ,if bo? l5g?s be ! same1 _! resi/ances are ! same & ! bridge balances4 ,n[ %ort5 "o cable & add resi/ance 9 s]ies ) x until ! bridge aga9 balances z 9 fig4 #eic4 ,! add$ resi/ance equals t ( ! piece cut (f4 ,h5ce1 if ! resi/ance p] foot be kn[n1 ! l5g? ( ! %ort] piece c be easily calculat$4 ,9 ! ,murray & ,v>ley te/s1 ! batt]y circuit is by gr\nd connections in/ead ( by wire4 ,9 ! ,murray loop ! arrangem5t is simil> to fig4 #eib1 ! batt]y circuit be+ complet$ by gr\nd connection ?r\gh fault 9 defective cable4 ,fig4 #eid %[s ! g5]al arrangem5t ( ! ,v>ley loop4 ,loop ,te/4--,?is is a me?od ( locat+ a fault 9 a telegraph or telephone circuit :5 !re is a good wire runn+ p>allel ) ! defective "o4 ,9 ! process1 ! good & bad wires are jo9$ at _! di/ant ends & "o t]m9al ( ! batt]y is connect$ to a ,:eat/one bridge1 :ile ! o!r t]m9al is gr\nd$4 ,!re are diff]5t ways ( mak+ loop te/s z by3 #a4 ,! ,murray loop2 #b4 ,! ,v>ley loop2 #c4 ,special loop4 ,illu/ration3 ,fig4 #eie4--,! ,murray loop te/4 ,! app>atus is connect$ z 9 ! figure4 ,! rheo/at ( ! bridge is us$ 9 place ( ! second arm to p]mit l>ge adju/m5t4 ,x & ,y are ! resi/ances ( ! cable betwe5 ! fault & ! po9ts #a & #b respectively4 ,! ,murray ,loop4--,9 ?is te/ only "o ( ! two regul> bridge arms is us$1 ! o!r be+ replac$ by ! rheo/at giv+ an arm ( l>ge adju/m5t4 ,! connections are %[n 9 fig4 #eie4 ,9 mak+ ! te/1 close key & note ! deflection ( ! ne$le due to pressure ( *emical action at fault1 if any4 ,?is is call$ ! false z]o4 ,n[ apply ! positive or negative pole ( ! batt]y by depress+ ! batt]y key1 & balance to ! false z]o previ\sly obta9$ by v>y+ ! resi/ance 9 arms ,a or ,b4 ,!n by ,:eat/one bridge =mula3 ,,rx,,ay1 & ,l,x,y2 ,y,l-,x1 :5ce ,x ,a_/7,r,a7 ,y ,l7,r_/7,b,a77 ,illu/ration3 ,fig4 #eif4--,murray loop me?od ( fault location ) ,le$s & ,nor?rup fault f9d]4 ,case ,i :]e !re are two wires hav+ equal resi/ance1 9 "o ( :i* !re is a fault4 ,connect & set swit*es z %[n2 jo9 ! good wire to po/ #a & ! faulty wire to po/ #b4 ,! resi/ance ( ,e is equal to t ( ,,ab4 ,f ! symmetry ( ! arrangem5t1 x is evid5t t1 if ! fault 7 exactly at ! junction betwe5 ! good & bad wires1 ! contact po9t ,c w\ld re/ = a balance at #a1jjj on ! scale1 or at #ejj if ! fault 7 half-way along ! bad wire2 h5ce1 at :atev] po9t x comes to re/1 ! read+ divid$ by #a1jjj & multipli$ by ! l5g? ( ! bad wire is ! di/ance f ! in/rum5t to ! fault4 ,,example--,9 a pair ( equal wires1 #e4h miles long1 "o is gr\nd$4 ,) ! connections made z above1 & ! galvanomet] balanc$ = ! dial read+ #abd1 ! di/ance to ! fault is 7#abd #eh7 #a1jjj 4#gaib miles4 ,illu/ration3 ,fig4 #eig4--,murray loop me?od ( fault location ) ,le$s & ,nor?rup fault f9d]3 ,case ,,ii1 :]e ! good & bad wires are unequal4 ,! figure %[s ! connections4 ,x is ! ord9>y ,murray loop & x is evid5t t ! resi/ance a1 to ! fault w be obta9$ f ! =mula a 7,a #a1jjj7 r1 :]e r is ! resi/ance ( ! loop1 & ,a is ! read+ ( ! contact ,c on its scale4 ,! di/ance d1 to ! fault is obta9$ f ! =mula d ,ar 7#a1jjj ,m71 :]e ,m is ! resi/ance p] mile ( ! faulty wire4 ,,example--,a wire hav+ a resi/ance ,m ( #af4df ohms p] mile is gr\nd$4 ,?is wire 0 loop$ ) a wire ( unkn[n resi/ance & ! total resi/ance ( ! loop r 0 measur$ & f\nd to be #ed4jg ohms4 ,connections 7 made z 9 ! figure1 & ! read+ ,a 0 f\nd to be #ccb4 ,sub/itut+ ^! values 9 ! above =mula3 d 7#ccb #ed4jg7 7#a1jjj #af4df7 #a4ji miles4 ,ques4 ,h[ may ! di/ance f #b to ! fault be det]m9$ 9 knots or miles4 ,ans4 ,divide ,y by resi/ance p] knot or mile4 ,! ,v>ley ,loop4--,?is is a me?od ( locat+ a cross or gr\nd 9 a telephone or telegraph l9e or o!r cable by us+ a ,:eat/one bridge 9 a loop =m$ ( a good wire & ! faulty wire jo9$ at _! di/ance ends4 ,"o t]m9al ( ! batt]y is gr\nd$ & ! o!r connect$ to a po9t on ! bridge at ! junction ( ! ratio arms4 ,! rheo/at arm !n includes ! resi/ance ( ! rheo/at plus ! resi/ance ( ! fault1 :ile ! unkn[n arm includes ! resi/ance ( ! good wire plus ! resi/ance ( ! bad wire beyond ! fault4 ,:5 ! bridge is balanc$1 ! unkn[n resi/ances may be readily det]m9$ by a simple equation4 ,illu/ration3 ,fig4 #eih4--,! ,v>ley loop te/4 ,! diagram %[s ! v>i\s connections4 ,x & ,y are ! resi/ances ( ! cable betwe5 ! fault & ! po9ts #a & #b respectively4 ,l is ! resi/ance ( ! good & bad cable or ,x ,y4 ,9 mak+ ! ,v>ley loop te/1 ! resi/ance ( loop$ cable or conductors is measur$1 & !n connect$ z 9 fig4 #eih4 ,close ! batt]y key & adju/ ,r = balance4 ,:5 e>? curr5t is pres5t1 ! be/ results are obta9$ :5 ! fault is cle>$ by ! negative pole1 & j be=e x beg9s to pol>ize4 ,if ,x be ! resi/ance f #b to ! fault1 !n ,x 7,l - ,r7 _/ #b also1 ,x divid$ by ! resi/ance ( ! cable or conductor p] knot or mile gives ! di/ance ( fault 9 knot or miles4 ,:5 ! resi/ance ( ! good wire us$ to =m a loop ) ! defective wire1 toge!r ) t portion ( ! defective wire f ! jo9t to ! fault is less ?an ! resi/ance ( ! defective wire f ! te/+ /ation to ! fault1 ! resi/ance ,r mu/ be ins]t$ betwe5 po9t #a & ! good conductor1 ! defective wire be+ connect$ directly to po9t4 ,! =mula 9 ?is case is ,x 7,l ,r7 _/ #b ,illu/ration3 ,figs4 #eii & #fjj4--,v>ley loop me?od ( fault location ) ,le$s & ,nor?rup fault f9d]4 ,?is me?od may be us$ z a *eck on ! ,murray me?ods4 ,connect ! faulty wire to #a1 & measure ! resi/ance ( ! loop4 ,!n ?r[ swit*es z %[n 9 ! fig4 #fjj4 ,let3 a resi/ance to fault1 d di/ance to ! fault 9 miles1 ,m resi/ance ( ! faulty wire p] mile1 r resi/ance ( ! loop1 ,r resi/ance ( ! coil ,r1 or #ajj ohms1 ,t ,a 7#a1jjj - ,a7 to be read f ! table4 ,f ! ,:eat/one bridge relation3 a 7r - #ajj,t7 7,t #a71 & d 7r - #ajj,t7 7,t #a7,m4 ,,example--,a wire hav+ a resi/ance ( #af4df ohms p] mile is gr\nd$4 ,?is 0 loop$ ) a wire ( unkn[n resi/ance & ! resi/ance ( ! loop 0 f\nd to be #ed4jg ohms4 ,connections 7 made z 9 ! figure1 & ! read+ ,a 0 f\nd to be #bcd4 ,f ! table ,t 4#cjee1 & sub/itut+3 d 7#ed4jg - #cj4ee7 7#a4cjee #af4df7 #a4jid miles4 ,special ,loop4--,?is me?od may be us$ to advantage :]e ! l5g? ( ! cable or faulty wire only is kn[n & :]e !re are two o!r wires :i* may be us$ to complete ! loop4 ,x is n necess>y t ! resi/ance ( ! faulty wire & ! l5g? & resi/ance ( ! o!r wires be kn[n4 ,figs4 #fja to #fjd %[ ! connections & me?od ( te/+4 ,,example4--,all ! wires 9 a cable #aj1heb ft4 long 7 f\nd to be gr\nd$ s t none ( !m c\ld be us$ z good wires4 ,two wires 7 select$ out ( ano!r cable go+ to ! same place by a diff]5t r\te & securely jo9$ to "o ( ! gr\nd$ wires at ! di/ant end4 ,?is gr\nd$ wire & "o ( ! good ones 7 connect$ z %[n 9 figs4 #fja & #fjb & ! read+ ,a 0 f\nd to be #cjg4 ,connections 7 !n made z %[n 9 figs4 #fjc & #fjd & ,a 0 f\nd to be #faj4 ,:at is ! value ( d8 ,accord+ to =mula d ,,al_/,a 7#cjg #aj1hec7_/faj #e1dfa ft4 ,illu/ration3 ,figs4 #fja & #fjb4--,special loop te/ ) ,le$s & ,nor?rup fault f9d]4 ,= ! fir/ measurem5t connect ! faulty wire to #b1 ei!r ( ! good wires1 z ,z1 to #a1 ! po/ ,gr to gr\nd1 & %ort circuit ! coils ,r & ,e by clos+ swit*es ,u & ,v z 9 ! figures4 ,balance 9 ! usual way & call ! dial read+ ,a4 ,= ! second measurem5t1 connect ! po/ ,gr4 7disconnect$ f gr\nd71 to ! o!r good wire y z %[n 9 figs4 #fjc & #fjd1 & get ano!r balance2 call ?is read+ ,a'4 ,! di/ance d1 to ! fault is det]m9$ f ! simple =mula d ,,al ,a' :]e ,l is ! l5g? ( ! cable or faulty wire4 ,illu/ration3 ,figs4 #fjc & #fjd4--,special loop te/ z made ) ! ,le$s & ,nor?rup fault f9d]4 ,diagram %[+ connections = ! second measurem5t4 ,! special loop te/ may be us$ to advantage :]e ! l5g? ( ! cable or faulty wire only is kn[n1 & :]e !re are two o!r wires :i* may be us$ to complete ! loop4 ,to use an outside batt]y1 connect "o pole to ,ba1 & gr\nd ! o!r4 ,! pressure ( ?is batt]y mu/ nev] exce$ #aaj volts2 if x be ov] #be volts1 see t swit* ,w is op54 ,! ,pot5tiomet]4--,= ! rapid & accurate measurem5t ( voltage1 curr5t1 & resi/ance1 ! pot5tiomet] c be recomm5d$4 ,^? 9 *>ge ( electric light & p[] companies1 & also ^? :o pur*ase l>ge am\nts ( electrical en]gy are realiz+1 m & m1 ! necessity ( hav+ satisfactory prim>y /&>ds ) :i* to *eck _! volt-1 amp]e-1 & watt-met]s4 ,:5 x is realiz$ t an error ( "o p] c5t4 9 a comm]cial in/rum5t means an error ( "o doll> "o way or ! o!r 9 e "o hundr$ doll>s *>g$1 ! ne$ ( su* /&>dization app>atus becomes at once app>5t4 ,! pot5tiomet]1 x %\ld be not$1 relies = its accuracy1 only ^u ! con/ancy & accuracy ( resi/ances & ^u /&>d cells4 ,) ! mat]ials n[ available1 & ! skill :i* has be5 acquir$ 9 _! manufacture1 bo? ! resi/ances & ! /&>d cells are obta9able :i* are rem>kably con/ant1 & bo? c be readily *eck$ = accuracy4 ,location ( ,op5s4--,^! measurem5ts are bas$ on ! fact t ! capacity ( wires 9 a cable is ord9>ily a measurable quantity1 :i*1 9 wire ( uni=m diamet]1 is proportionate to l5g?4 ,9 mak+ ^! te/s1 a fault f9d] is us$ toge!r ) a buzz]1 dry cells to op]ate x1 small induction coil1 & telephone receiv]4 ,^! in/rum5ts are to be f\nd 9 any telephone ex*ange4 ,x is be/ to locate ! buzz] at "s di/ance f ! fault f9d] 9 ord] t x _c be he>d by ! op]ator4 ,illu/ration3 ,fig4 #fje4--,to use galvanomet] ( ,le$s & ,nor?rup fault f9d] 9 s]ies ) ! batt]y3 ,set swit*es z %[n1 & connect betwe5 po/s ,gr4 & #b 7see figs4 #ehg & #ehh74 ,! galvanomet] w h ! maximum s5sibility ) ! po9t] at #a1jjj & ! m9imum at z]o4 ,illu/ration3 ,fig4 #fjf4--,to measure high resi/ances1 su* z ! resi/ances ( faults ) ,le$s & ,nor?rup fault f9d]4 ,fir/ ,me?od4--,arrange ! swit*es z %[n 9 ! figure4 ,connect po/s ,gr4 & #b1 turn ! h&le until ! galvanomet] ne$le comes to re/ at an ev5 deflection ( t5 divisions4 ,call ! read+ ,a4 ,connect 9 ! unkn[n resi/ance betwe5 ,gr4 & #b4 ,n[ close ! swit* ,w1 s t ! figure #a appe>s on ! top ( ! block1 & aga9 br+ ! galvanomet] to a deflection ( t5 divisions & call ! read+ ,b4 ,!n ,x 7#aj1jjj ,b ,a7 - #a1jjj4 ,9 case ,x be a high resi/ance1 x w be f\nd t ! galvanomet] w n deflect t5 divisions = any position ( ! po9t]4 ,9 su* case1 *oose a numb] ( divisions :i* is a factor ( t51 su* z #e1 #b1 or #a1 & multiply 7#aj1jjj ,b ,a7 by t5 divid$ by ! numb] *os51 z #aj_/e1 #aj_/b1 #aj_/a4 ,= example1 = a deflection ( two divisions3 ,x 7#aj_/b77aj1jjj ,b ,a7 - #a1jjj4 ,! satisfactory range ( ! set = high resi/ance measurem5t may be increas$ by us+ an outside batt]y ( high] voltage4 ,) ! conta9$ batt]y1 satisfactory measurem5ts c be made up to #a or #b megohms4 ,:5 outside batt]y is us$1 connect "o t]m9al to ! po/ ,ba1 & ! o!r to #b = ! read+ ,a4 ,connect ! batt]y & unkn[n resi/ance 9 s]ies betwe5 ^! po/s = ! read+ ,b4 ,:5 an outside pressure ( #be volts or ov] is us$1 ! swit* ,w %\ld n be clos$ unless !re be a resi/ance 9 s]ies ) ! batt]y ( #aj1jjj ohms or ov]4 ,second ,me?od4--,= use z a voltmet] to measure high resi/ances4 7,m conv5i5t b n q z accurate z fir/ me?od47 ,set ! swit*es to ,,rv1 ,m & #aj4 ,turn ! knurl$ nut on ! galvanomet] s z to set ! ne$le to ! extreme "r h& side ( ! scale4 ,connect ! po/s #b & ,gr4 ) a %ort piece ( wire4 ,turn ! rotat+ po9t] on ! scale until ! galvanomet] ne$le moves ov] ab\t #bj scale divisions :5 ! batt]y key is clos$4 ,remove ! connection betwe5 #b & ,gr4 z ! voltmet] t]m9als4 ,?is makes a simple way ( te/+ = v>i\s k9ds & am\nts ( tr\ble4 ,on a wet cable a deflection ( #aj to #ae divisions indicates heavy en\gh tr\ble to locate ) ! fault f9d]4 ,) a little c>e1 tr\ble %[+ only #e or #f divisions c be locat$4 ,be=e attempt+ locations = op5s x is well to make ! foll[+ measurem5ts3 #a4 ,! insulation ( ! brok5 wire & ! insulation ( ! good wire ) :i* x is to be comp>$4 ,?is may be done z %[n 9 fig4 #fjf4 ,x is be/ t ! insulation resi/ance be fairly good1 b exp]im5ts indicate t good results c be obta9$ by ! me?ods :i* foll[1 ev5 :5 ! insulation is z l[ z #ajj1jjj ohms1 & fair results :5 z l[ z #ej1jjj to #ajj1jjj ohms4 ,illu/ration3 ,fig4 #fjg4--;,diagram ( connections 9 te/+ = op5s ) ,le$s & ,nor?rup fault f9d]4 ,! app>atus requir$ consi/s ( fault f9d]1 buzz]1 dry cell to op]ate buzz]1 small induction coil1 & telephone receiv]4 ,connect ! batt]y to ! prim>y ( ! induction coil1 "o t]m9al ( ! second>y to ! po/ ,ba1 & ! o!r to ! connect$ wires z %[n4 ,set swit*es ,u & ,v s z to %ort circuit ! two resi/ance coils4 #b4 ,! resi/ance betwe5 ! two sections ( ! brok5 wire %\ld be measur$4 ,?is may be done by jo9+ ! brok5 wire & a good wire at ! di/ant end ( ! cable & measur+ ! resi/ance ( ! loop4 ,to ensure close locations1 ?is resi/ance %\ld be ov] #ajj1jjj ohms4 ,fair locations c be made :5 ! resi/ance is mu* l[] & x is wor? :ile to attempt x ev5 if ! resi/ance be z l[ z #aj1jjj ohms4 ,! difficulty ( det]m9+ ! balance po9t increases z ! resi/ance decreases4 ,ques4 ,describe ! me?od ( locat+ an op5 ) a fault f9d]4 ,ans4 7,case ,i7 ,! brok5 wire w be "o ( a pair4 ,select ano!r pair 9 ! cable t w h ! same capacity p] mile & jo9 toge!r ! mate ( ! brok5 wire & "o wire ( ! o!r pair4 ,make ! connections z %[n 9 fig4 #fjg1 !n depress ! batt]y key & move ! contact to ! po9t ( m9imum s\nd 9 ! telephone4 ,! di/ance to ! break is equal to ,,la 7#a1jjj - ,a71 :]e ,l is ! l5g? ( ! good wire4 ,,example3 ,a cable #a4de miles long conta9$ a brok5 wire4 ,x 0 f\nd t ! insulation resi/ance ( ! end ( ?is wire 0 ov] #aj megohms1 z 0 t ( ! good pair select$ to te/ aga9/ x4 ,! resi/ance betwe5 ! two pieces ( ! good wire 0 also ov] #aj megohms4 ,connections 7 made z 9 fig4 #fjg1 & x 0 f\nd t ! balance po9t 0 #dgf4 ,accord+ly f ! table ,a _/ 7#a1jjj - ,a7 #j4ijhd & d #a4de 4#ijhd #a4cag miles4 ,illu/ration3 ,fig4 #fjh4--;,diagram ( connections 9 te/+ ) ,le$s & ,nor?rup fault f9d] = op5 wire 9 telegraph & o!r cables 9 :i* ! wires are n gr\p$ 9 pairs4 ,connect ! brok5 wire to #a4 ,select a good wire & jo9 to #b4 ,connect all o!r wires & gr\nd !m1 by connect+ to ! cable %ea?4 ,connect ! di/ant end ( ! brok5 wire to ! o!rs4 ,gr\nd ! end ( ! induction coil t is n connect$ to ! po/ ,ba4 ,location ( ,op5s4--7,case ,,ii7 ,op5 wire 9 telegraph or o!r cables 9 :i* ! wires are n gr\p$ 9 pairs4 ,! connections are made z 9 fig4 #fjh1 & ! measurem5t & calculation exactly z 9 ! prec$+ case4 ,! accuracy ( ! location ( bo? ( ! above me?ods dep5ds on ! good & brok5 pair1 or ! good & brok5 wires hav+ equal & uni=m capacity p] unit l5g?4 ,x is n always possible to select wires t are alike 9 ?is respect4 ,9 su* cases1 z = in/ance1 :]e !re is no good wire 9 ! cable conta9+ ! brok5 wire1 & a good wire has to be select$ f ano!r cable1 ! me?od ( ,case ,,iii may be us$4 ,illu/ration3 ,fig4 #fji4--;,diagram ( connections = read+ 9 te/+ = op5s ) ,le$s & ,nor?rup fault f9d]1 :5 brok5 wire & good wire are n 9 ! same cable4 ,illu/ration3 ,fig4 #faj4--,le$s & ,nor?rup pot5tiomet]4 ,x is direct read+ f 4#jjjjja volt to #af volts1 & ) accessories ! range may be ext5d$ to #afjj volts1 & curr5ts may be measur$ up to #cjjj amp]es4 ,! in/rum5t has fifte5 coils ( #e ohms ea*1 :i* are 9 s]ies ) an ext5d$ wire ab\t #aij long ( equal resi/ance4 ,! electrical circuits are %[n 9 ! diagram fig4 #faa4 ,x is well = ! us] to op5 up ! pot5tiomet] & make himself famili> ) its int]ior con/ruction1 9 ord] to fully und]/& ! op]ation ( ! rheo/at & o!r p>ts4 ,!re are no contact resi/ances 9 ! pot5tiomet] circuit prop]4 ,! pot5tiomet] has l[ int]nal resi/ance :i* gives x ! maximum s5sibility4 ,comp>$ ) high resi/ance pot5tiomet]1 ?is is especially advantage\s 9 measur+ ! electromotive =ce ( !rmoc\ples1 & ! fall ( pot5tial across /&>d l[ resi/ances4 ,z con/ruct$1 ! la/ "o-t5? volt is cov]$ by ! ext5d$ wire & ! h&le :i* c>ries ! contact po9t on ! wire may be manipulat$ rapidly s t a fluctuat+ voltage may be accurately foll[$4 ,:5 us$ ) any cadmium cell1 ! pot5tiomet] is direct read+4 ,! accuracy ( ! pot5tiomet] resi/ances c be v]ifi$ ) ! facilities ( ! ord9>y laboratory4 ,location ( ,op5s4--,case ,,iii1 9 :i* ! brok5 wire & good wire are n 9 ! same cable4 ,connect ! good wire & brok5 wire 9 ! same way z %[n 9 fig4 #fjg1 & set ! po9t] = a balance4 ,call ! read+ ,a4 ,!n connect ! good wire & ! brok5 wire at ! di/ant end & set ! po9t] = a new balance4 ,call ?is ,a'4 ,! connections = ?is read+ are %[n 9 fig4 #fji4 ,! di/ance to ! break w be d 7,a ,a' ,l7 _/ 7#a1jjj7;,a - ,a'7 ,a ,a'7 :]e ,l is ! total l5g? ( ! brok5 wire4 ,illu/ration3 ,fig4 #faa4--;,diagram %[+ connections ( ,le$s & ,nor?rup pot5tiomet]4 ,! coils 9 ! s]ies ,,ad are ea* #e ohms1 & betwe5 ea* two !re is a brass block ) a ream$ hole4 ,a pair ( flexible cords ) tap] plug t]m9als to fit ^! holes is furni%$4 ,^! coils c be measur$ ) an ord9>y ,:eat/one bridge & ?us comp>$ ) ea* o!r to a high degree ( accuracy1 ev5 if ! bridge be n accurate4 ,= pot5tiomet] "w1 ! ess5tial po9t is t !y %\ld be l ea* o!r1 n t !y %\ld be accurately any p>ticul> value4 ,9 ! same way ! resi/ance ( ! ext5d$ wire c be comp>$ ) ! resi/ance ( ! coils 9 ,,ad4 ,its resi/ance %\ld be #a4a times ! value ( any coil betwe5 ,a & ,d4 ,outside connection ) ! ext5d$ wire may be made by us+ ! po/s m>k$ ,,br & -,,ba4 ,?is adju/m5t = balanc+ an unkn[n electromotive =ce is accompli%$ by ! manipulation ( ! two contact po9ts ,m & ,m'4 ,! coils ,,ad are arrang$ 9 a circle1 a revolv+ swit* mov+ ,m4 ,a *eck+ device enables ! op]ator to set ?is swit* )\t tak+ 8 eye f ! galvanomet]4 ,! resi/ance ,s is ( su* value t :5 x %unts ! wire ,,ob1 ! total resi/ance betwe5 ,o & ,b is #a_/aj ( ! same un%unt$4 ,:5 ! %unt is appli$1 provid$ ! total curr5t rema9 ! same1 ! drop betwe5 any two po9ts on ,,ab w be #a_/aj ( its previ\s value4 ,! total curr5t w rema9 ! same provid$ ! total resi/ance 9 ! circuit rema9 ! same4 ,?is is accompli%$ by mak+ ! coil ,k su* t x exactly comp5sates = ! r$uction 9 resi/ance caus$ by plugg+ 9 ! %unt coil ,s4 ,! l[ scale is appli$ by mov+ ! plug f ! position #a to ! position 4#a4 ,) ?is *ange ! pot5tiomet] reads f 4#af volt d[n by indicat$ /eps ( 4#jjjjje volt4 ,! read+ is v simple4 ,= in/ance1 if ,m /& at #a4b & ,m' at #a4ce revolutions1 ! read+ is #a4bace volts4 ,! resi/ances ( ! in/rum5t are w\nd ^u metal spools1 & are !re=e able to dissipate a comp>atively l>ge am\nt ( en]gy4 ,?is all[s ! pot5tiomet] to be us$ = pressure measurem5ts up to #af volts )\t ! use ( a volt box4 ,illu/ration3 ,fig4 #fab4--;,diagram %[+ actual connections 9 ! rheo/at ( ,le$s & ,nor?rup pot5tiomet]4 ,! figure corresponds to ,r ( fig4 #faa4 ,! rheo/at is m\nt$ 9 ! end ( ! pot5tiomet] z %[n 9 fig4 #faj4 ,r\gh adju/m5t ( ! pot5tiomet] curr5t is made by means ( ! v>iable resi/ance ,r4 ,f9e adju/m5t is made by means ( ! v>iable resi/ance ,r'4 ,x w be not$ t ! #bc ohm resi/ance ( ?is latt] rheo/at is %unt$ by a resi/ance ( #f4a ohms1 mak+ possible a v f9e regulation4 ,fur!r1 !re is 9 s]ies ) ! mov+ contact a resi/ance ( #djj ohms1 :i* makes ! effect ( v>iable contact resi/ance negligible4 ,only "o cell ( /orage batt]y %\ld be us$4 ,:5 ?is batt]y is fre%1 ! plug %[n 9 ! figure at #b,r %\ld be ins]t$ at ,r4 ,?is gives ! greate/ resi/ance 9 ! rheo/at circuit4 ,z ! cell runs d[n1 ! plug %\ld be *ang$ to #b,r4 ,:5 bo? plugs are 91 ! rheo/at slide wires are 9 s]ies ) ! pot5tiomet] circuit4 ,,example3 ,a pair ( wires conta9+ "o brok5 wire 0 connect$ ) a good pair 9 a diff]5t cable z %[n 9 fig4 #fjg4 ,! read+ ,a 0 f\nd to be #ahj4 ,! good & bad wires 7 !n jo9$ at ! di/ant end z 9 fig4 #fji1 & ! read+ ,a 0 f\nd to be #hh4 ,! total l5g? ( ! bad wire ,,mn 0 #a4dd miles4 ,requir$1 ! di/ance to ! break4 ,sub/itut+ ! values 9 ! =mula3 d #ahj #hh #a4dd _/ #a1jjj7ahj - #hh7 #ahj #hh 4#baa mile4 ,to ,pick ,out ,faulty ,wires 9 a ,cable4--,%ort circuit ! coils ,e & ,r ) swit*es ,u & ,v4 ,set ! po9t] at #a1jjj4 ,connect ! po/ ,gr4 to gr\nd or ! cable %ea? & apply ! wires "o aft] ano!r to ! b9d+ po/ #b4 ,! galvanomet] w deflect = a faulty wire4 ,illu/ration3 ,fig4 #fac4--;,diagram ( ! ,crompton pot5tiomet]4 ,9 ?is in/rum5t ! resi/ance consi/s ( f\rte5 coils1 ea* ( #aj ohms1 9 s]ies ) a /raight wire1 also #aj ohms resi/ance1 ?us =m+ a sy/em ( fifte5 equal /eps4 ,across ! :ole a pressure ( #a4e volt is appli$ f a second>y cell1 ?us provid+ 4#aj volt p] /ep4 ,any fraction is !n tapp$ (f by means ( a radial swit* on ! resi/ance coils & a slid+ contact on ! wire4 ,! /&>dization is p]=m$ by adju/+ a resi/ance 9 s]ies ) ! :ole until ! /&>d cell employ$ indicates1 by means ( ! galvanomet] ,g1 a balance at ! po9t :i* repres5ts its electromotive =ce on ! basis giv5 above4 ,ques4 ,:at is a pot5tiomet]8 ,ans4 ,an arrangem5t ( c>efully /&>diz$ resi/ances = measur+ voltages 9 comp>ison ) a /&>d cell4 ,x is us$ = accurate measurem5t ( voltages1 curr5ts1 & resi/ances4 ,9 place ( a s]ies ( /&>diz$ resi/ances1 a slide wire may be us$ z 9 fig4 #fad4 ,ques4 ,describe "o =m ( pot5tiomet]4 ,ans4 ,z %[n 9 fig4 #fad1 x consi/s ( a f9e ,g]man silv] wire ab\t #c feet long /ret*$ betwe5 ! b9d+ po/s ,a1 ,b1 :i* are atta*$ to a wood5 base c>ry+ a scale divid$ into #a1jjj equal p>ts4 ,!re are ?ree circuits1 ! t]m9al ,a be+ includ$ 9 ea*1 "o includ+ ! batt]y1 & ! o!r two ! galvanomet]4 ,a ?ree po9t swit* connects ! galvanomet] 9 s]ies ) ! /&>d cell ,,sc1 or ! cell to be te/$ ,c1 ! circuits be+ complet$ by leads t]m9at+ 9 ! slid+ contacts ,m & ,s4 ,illu/ration3 ,fig4 #fad4--;,diagram ( pot5tiomet] %[+ me?od ( measur+ ! voltage ( a cell4 ,! pot5tiomet] is simply a high resi/ance wire ( uni=m diamet] /ret*$ betwe5 two b9d+ po/s1 ,a & ,b1 9 su* a way t contact c be made at its ends & along its l5g?4 ,necess>y circuits are pla9ly %[n 9 ! figure2 ,,sc1 is a /&>d cell & ,c1 ! cell to be te/$4 ,m1 & ,s are slid+ contacts1 connect+ ) ! slide wire4 ,ques4 ,describe ! me?od ( measur+ ! voltage ( a cell ) a pot5tiomet]4 ,ans4 ,fig4 #fad %[s a me?od ( comp>+ a pressure ) t ( a /&>d cell & is applicable :e!r ! pressure ( ! cell to be te/$ be great] or less ?an t ( ! /&>d cell4 ,9 mak+ ! te/ ! swit* ,f is fir/ clos$1 !n ! o!r swit* is mov$ to ,d1 & ,m adju/$ till galvanomet] %[s no deflection2 simil>ly1 ! swit* is mov$ to ,g1 & ,s adju/$ till galvanomet] %[s no deflection4 ,!n1 ,c3,,sc ,,z3,,am4 f :i* ,c ,,sc ,,z ,,am4 ,,example4--,let #a4jaf volts be ! kn[n voltage ( ! /&>d cell ,,sc1 & ! scale read+ ( ,,z be #feg1 & ( ,,am1 #bbe z 9 ! figure1 !n ,c 7#a4jaf #feg7 _/ #bbe #b4iff volts ,! arrangem5t may1 h[ev]1 be made direct read+1 t is1 ! slide wire may h a scale ( volts in/ead ( l5g?s or resi/ances1 z foll[s3 ,suppose ! /&>d cell to h a pressure ( #a4dcd volts1 ! slid+ contact ,m is plac$ at ! read+ #a4dcd1 & ! adju/able resi/ance v>i$ till ! galvanomet] %[s no curr5t4 ,?is means t ! pressure betwe5 ,a & ,m is #a4dcd1 & consequ5tly ! pressures all along ! slide c be read (f ! scale 9 volts4 ,h5ce1 :5 ,s has be5 adju/$ to balance1 ! pressure ( ,c is read (f ! scale 9 volts4 ,illu/ration3 ,fig4 #fae4--,to measure a pressure great] ?an #a4f volts ) ,le$s & ,nor?rup pot5tiomet] by us+ a volt box or multipli]4 ,to measure high voltages x is necess>y to connect ! voltage across high resi/ance & to measure on ! pot5tiomet] a def9ite fraction ( ! total drop4 ,9 ! figure1 ,,ab is a high resi/ance ( :i* ,,cb is 4#a?1 ,,db 4#ja?1 & ,,eb 4#jja? ( ! total resi/ance4 ,! pot5tiomet] read+ is accord+ly multipli$ by #aj1 #ajj1 or #a1jjj1 dep5d+ ^u :e!r ! swit* ,m is set on ,c1 ,d1 or ,e4 ,resi/ance boxes = ?is purpose are call$ volt boxes1 & are con/ruct$ to multiply ! pot5tiomet] read+s by #aj1 #ajj1 & #a1jjj4 ,9 us+ !m1 x is only necess>y to connect ! unkn[n ,e4,m4,f4 at ! po/s s m>k$1 & ! pot5tiomet] to ! po/s m>k$ ,p4 ,! pot5tiomet] read+ is tak5 z above & multipli$ by a factor dep5d+ ^u ! position ( ! swit* ,m1 :i* factor is indicat$ ^u ! box4 ,x is ess5tial 9 mak+ ^! connections t ! pol>ity be c>efully obs]v$4 ,h[ to ,use a ,pot5tiomet]4--,all connections mu/ be made z indicat$ by ! /amp+ on ! in/rum5t4 ,p>ticul> att5tion mu/ be giv5 to ! pol>ity ( ! /&>d cell1 ( ! batt]y1 & ( ! voltage1 ! correspond+ & - signs be+ m>k$4 ,if us$ ) a wall galvanomet] hav+ a telescope & scale1 x w be f\nd conv5i5t to place ! pot5tiomet] s t ! telescope is directly ov] ! glass index ( ! ext5d$ wire1 ?us p]mitt+ ! obs]v] to read ! galvanomet] deflections & pot5tiomet] sett+s )\t *ang+ 8 position4 ,pot5tiomet] ,curr5t4--,a m$ium siz$ /orage cell w be f\nd desirable1 produc+ a /eady curr5t4 ,errors 9 measurem5ts are frequ5tly made by us+ an un/eady curr5t4 ,sett+ = ,/&>d ,cell4--,set ! /&>d cell to correspond ) ! c]tifi$ pressure ( ! /&>d cell z giv5 9 its c]tificate4 ,9 us+ ! pot5tiomet] %[n 9 fig4 #faj1 place ! plug 9 hole #a1 & see t x is always 9 ?is position :5 *eck+ aga9/ ! /&>d cell4 ,place ! d\ble ?r[ swit* at ,,/d4 ,,cell4 ,adju/ ! regulat+ rheo/at until ! galvanomet] %[s no deflection4 ,9 mak+ ! fir/ adju/m5t use ! key m>k$ ,r#a2 :5 a balance is almo/ atta9$1 use key ,r#b1 & = ! f9al adju/m5t use key m>k$ ,r#j4 ,?is cuts out ! resi/ance 9 s]ies ) ! galvanomet] & gives ! maximum s5sibility4 ,measurem5t ( ,unkn[n ,pressure4--,! pot5tiomet] 7fig4 #faj71 z ord9>ily us$1 gives direct read+s = voltages up to & includ+ #a4f volts4 ,= pressures high] ?an #a4f volts1 a volt box or multipli] %\ld be us$4 ,aft] obta9+ ! /&>d cell balance1 z previ\sly describ$1 place ! d\ble ?r[ swit* 9 ! position m>k$ ,e4,m4,f4 ,! balance = ! unkn[n ,e4,m4,f4 is obta9$ by manipulat+ ! t5?s swit* & rotat+ ! contact on ! ext5d$ pot5tiomet] wire4 ,! f9al position ( ! two contacts 9 conjunction ) ! position ( ! plug at ! left ( ! in/rum5t indicates ! voltage "u te/4 ,z direct$ above1 use key ,r#a = r\gh adju/m5t1 ,r#b = int]m$iate adju/m5t1 & key ,r#j = f9al adju/m5t4 ,plug at #a gives read+s = voltage directly f sett+s ( t5?s swit* & ext5d$ wire contact4 ,plug at 4#a %unts ! pot5tiomet] circuit s t ! voltage measur$ is 4#a ( ! read+ tak5 directly f ! scale4 ,h5ce1 ! read+s tak5 f ! sett+ ( ! t5?s swit* & ! slide wire contact mu/ be divid$ by #aj4 ,to ,balance ,galvanomet] = ,unkn[n ,voltage4--,place plug 9 hole #a 7fig4 #faj7 = voltages up to #a4f1 & 9 hole 4#a = voltages up to 4#af4 ,rotate ! t5?s swit* until a condition ( balance is obta9$ exactly or approximately4 ,to secure an exact balance1 rotate ! contact on ! ext5d$ wire4 ,! unkn[n voltage c n[ be read directly f ! position ( ! t5?s swit* & ! ext5d$ wire contact if plug be at #a1 or by divid+ by #aj if plug be at 4#a4 ,,example4--,a balance 0 obta9$ ) ! t5?s swit* at #a4c1 ! ext5d$ wire contact at #agf & ! plug at #a4 ,! voltage "u te/1 !re=e1 is #a4cagf4 ,if ! plug at 4#a _h be5 us$1 ! same read+ w\ld h indicat$ 4#acagf4 ,to asc]ta9 if ! curr5t 9 ! pot5tiomet] circuit has alt]$ dur+ a measurem5t1 x is only necess>y to plug 9 at #a1 place ! d\ble ?r[ swit* on ,,/d4 ,,cell & close ! galvanomet] key4 ,no deflection indicates t ! curr5t has n *ang$4 ,if ! galvanomet] deflect1 ! regulat+ rheo/at mu/ aga9 be adju/$ until ! galvanomet] %[s no deflection4 ,to ,measure ,voltages f #a4f to #af4--,pressures up to #af volts may be measur$ by us+ a great] voltage across ! ,,ba po/s 7fig4 #fae74 ,= ?is purpose a batt]y ( ab\t #bj volts %\ld be us$4 ,ins]t ! l>ge plug at 4#a & ?r[ ! swit* to ,,/d4 ,,cell1 !n balance ! galvanomet] by means ( ! regulat+ rheo/at4 ,:5 ! rheo/at has be5 set to secure a balance1 ins]t ! l>ge plug at #a1 set ! swit* on ,e4,m4,f4 & read ! voltage 9 ! usual mann]4 ,multiply ! read+ by #aj4 ,illu/ration3 ,fig4 #faf4--,measurem5t ( curr5t ) pot5tiomet]4 ,?is is done by measur+ ! drop 9 volts across a kn[n l[ resi/ance4 ,9 ! figure ,s is ! /&>d resi/ance1 & on x are ! pressure t]m9als pp1 & ! curr5t t]m9als ,,cc4 ,! pot5tiomet] is connect$ to ! %unt ?r\gh ! po/s m>k$ ,p4 ,! resi/ance betwe5 ! po9ts pp is adju/$ to an ev5 fraction ( an ohm4 ,^! resi/ances are s *os5 t 9 ord] to det]m9e ! curr5t pass+ ?r\gh ! %unt1 aft] hav+ obta9$ a pot5tiomet] balance x is only necess>y to multiply ! pot5tiomet] read+ by a simple factor4 ,= in/ance1 9 us+ a 4#ja ohm /&>d4 ,x is only necess>y to multiply ! pot5tiomet] read+ by #ajj1 :i* gives ! curr5t read+ 9 amp]es2 simil>ly1 a 4#a ohm requires multiplication by #aj1 & a 4#jja ohm by #a1jjj4 ,c>e ( ,pot5tiomet]4--,! slide wire1 al?\gh protect$ to a great ext5t by ! hood1 9 "t accumulates du/ & dirt ) a ?9 film ( oxide4 ,?is w t5d to increase ! resi/ance 9 ?is "p ( ! circuit ow+ to poor contact4 ,?is wire %\ld1 !re=e1 be clean$ occasionally4 ,to d ?is1 unscrew ! /op aga9/ :i* ! hood /rikes :5 turn$ to read z]o2 !n remove ! hood & rub ! entire slide wire vigor\sly ) a s(t clo? dipp$ 9 vasel9e4 ,d n use em]y or s& pap] z ?is w de/roy ! uni=mity ( ! slide wire4 ,clean also ! /eel contact :i* rubs on ! wire1 z ?is becomes glaz$ aft] mu* use4 ,:5 ! pot5tiomet] is n 9 use1 ! hood %\ld be screw$ all ! way d[n1 & ! lid put 9 place to exclude du/4 ,if x be us$ 9 a *emical factory1 laboratory1 or any place :]e acid fumes are preval5t1 ?is latt] precaution is important1 because ! fumes may attack ! slide wire4 ,x is also well to keep ! contact surfaces ( ! swit* /uds clean & bright by wip+ !m occasionally ) a s(t clo? dipp$ 9 vasel9e4 ,illu/ration3 ,res4 ( leads on ea* end is equal to #aj divisions ( slide wire4 ,! slide wire is divid$ into #ajjj p>ts--#bj = ! leads1 or #ihj divisions4 ,calibrat$ scale on ,galvanomet]3 ,fig4 #fag4--;,diagram ( ,le$s & ,nor?rup bridge = locat+ faults 9 p[] circuits1 %[+ arrangem5t ( ! connections includ+ ! lead cables & galvanomet] contacts4 ,make connections z %[n4 ,! clamps mu/ be s fa/5$ at ,a & ,c t ! contact resi/ances w be v small4 ,?is contact resi/ance w figure z an error 9 ! measurem5t4 ,if1 = in/ance1 ! contact resi/ance 7 equal to 4#jja ( an ohm1 & ! wire 7 ( su* a size t 4#jja ( an ohm 7 equal to ! resi/ance ( #bj feet ( ! cable1 !re w\ld be an error ( #bj feet 9 ! location ( ! fault4 ,= ?is reason all contact resi/ances ?r\gh\t ! loop f ,a to ,c mu/ be extremely small4 ,! batt]y is to be connect$ to ! po/s m>k$ ,ba41 & ! po/ m>k$ ,gr4 is to be gr\nd$4 ,x w v frequ5tly happ5 t ! gr\nd is to ! cable %ea? or "s o!r conductor4 ,9 ?is case1 ! b9d+ po/ ,gr4 %\ld be gr\nd$ to ?is conductor4 ,suffici5t batt]y %\ld be us$ to give a readable deflection on ! galvanomet] = a small movem5t ( ! contact on ! bridge wire4 ,! fault is locat$ by ! usual ,murray =mula4 ,if1 = in/ance1 ! galvanomet] %[ no deflection :5 ! contact is at #cjj on ! scale1 x w\ld indicate t ! fault is at a di/ance f ,a equal to 4#jjc ( ! total l5g? ( ! loop f ,a to ,c4 ,a te/+ curr5t ( five amp]es may be us$ ) ?is bridge4 ,9 cases ( necessity1 ?is curr5t may be increas$ to eight amp]es1 b :5 ?is curr5t is us$ x %\ld n be all[$ to pass ?r\gh ! bridge = a long] "t ?an is necess>y4 ,x frequ5tly happ5s t small faults :i* h a v high resi/ance develop 9 high pressure cables4 ,su* faults are likely to break d[n & result 9 damage & %\ld be locat$4 ,x is usually impossible to locate ^! faults until !y h be5 p>tially c>boniz$4 ,?is mu/ be done by apply+ a suffici5tly high voltage betwe5 ! cable & ! %ea? 7or :atev] x is gr\nd$ on7 to break d[n ! fault4 ,9 ord] to prev5t ! break+ d[n process f result+ 9 a s]i\s burn out a high resi/ance mu/ be plac$ 9 ! circuit :i* w prev5t an excessive curr5t1 or ! circuit mu/ be c>efully fus$4 ,! =m] proc$ure is ! bett]4 ,location ( ,faults :]e ! ,loop is ,compos$ ( ,cables ( ,diff]5t ,cross ,sections4--,faults 9 loops ( ?is "* may be locat$ ) ! same degree ( accuracy z ^? 9 loops ( a uni=m cross section1 provid$ ! l5g? & cross section ( ea* l5g? ( cable are kn[n4 ,an example w illu/rate ! me?od3 ,9 ! diagram1 fig4 #fag1 assume ! l5g? ( ! cable ,,ae to be #eej y>ds ( #be1jjj cir4 mil41 ,,ef1 #ejj y>ds ( #dj1jjj cir4 mil41 & ,,fc1 #a1jej y>ds ( #cj1jjj cir4 mil4 ,^! l5g?s mu/ be r$uc$ by calculation to equival5t l5g?s ( "o size1 & = ?is purpose x is be/ to select ! l>ge/ size4 ,! results ( ?is calculation are z foll[s3 #eej yds4 ( #be1jjj cir4 mil4 #hhj yds4 ( #dj1jjj cir4 mil4 #ejj #dj1jjj #ejj #dj1jjj #a1jej #cj1jjj #a1djj #dj1jjj ,?is makes ! total resi/ance ( ! loop equival5t to #b1ghj y>ds ( #dj1jjj cir4 mil4 ,if ! contact %[ a balance = a read+ ( #cgb4e1 ?is indicates t ! fault is at a di/ance ( #cgb4e_/a1jjj ( #b1ghj #a1jce4e equival5t y>ds4 ,( ?is1 #hhj are 9 ! /ret* ,a ,e4 ,consequ5tly ! fault is3 #a1jce4e - #hhj #aee4e y>ds f ,e4 ,illu/ration3 ,fig4 #fah4--,! ,fis*] portable cable te/+ set1 design$ = locat+ crosses1 gr\nds & breaks 9 cables1 also = conductor & liquid resi/ance measure4 ,! di/+ui%+ feature ( ! set is ! ma/] swit*4 ,by means ( ?is swit*1 connections c be made = ! v>i\s te/s by a s+le movem5t1 ?us avoid+ ! labor & "t :i* h to be exp5d$ 9 int]*ang+ ! connections & memoriz+ ! r complicat$ s*eme ( connections4 ,,*apt] ,,xxviii ,,ammet]s1 ,,voltmet]s ,,& ,,wattmet]s4 ,an ammet] or amp]e met] is simply a comm]cial =m ( galvanomet] s con/ruct$ t ! deflection ( ! ne$le indicates directly ! /r5g? ( curr5t 9 amp]es4 ,a good ammet] %\ld h a v l[ resi/ance s t v little ( ! en]gy ( ! curr5t w be absorb$2 ! ne$le %\ld be dead beat1 & suffici5tly s5sitive to respond to m9ute v>iations ( curr5t4 ,accord+ to ! pr9ciple ( op]ation1 ammet]s & voltmet]s are classifi$ z3 #a4 ,mov+ iron2 #b4 ,mov+ coil2 #c4 ,sol5oid or plung]2 #d4 ,magnetic vane2 #e4 ,hot wire2 #f4 ,electro/atic2 #g4 ,a/atic2 #h4 ,incl9$ coil2 #i4 ,fix$ & movable coil4 ,aga91 !y are divid$ accord+ to _! use into two classes3 #a4 ,portable type2 #b4 ,swit*bo>d type4 ,milli-ammet]s or milli-voltmet]s are in/rum5ts 9 :i* ! scale is graduat$ to read directly 9 ?\s&?s ( an amp]e or ?\s&?s ( a volt respectively4 ,ques4 ,describe ! mov+ iron type in/rum5t4 ,ans4 ,! arrangem5t ( ! work+ p>ts are %[n 9 fig4 #fbj4 ,a s(t iron ne$le ,n1 is pivot$ inside ( a coil ,c1 & is held out ( l9e ) ! axis ( ! coil by means ( a p]man5t magnet ,m1 :5 ! in/rum5t is idle4 ,9 ?is position1 a po9t] ,p1 :i* is atta*$ to ! ne$le1 /&s at ! z]o m>k ( ! scale ,s4 ,if a curr5t be pass$ ?r\gh ! coil1 magnetic l9es ( =ce are set up 9 its c5t]1 :i* t5d to pull ! ne$le into l9e ) !m1 & !re=e ) ! axis ( ! coil4 ,?is pull is resi/$ by ! p]man5t magnet ,m1 & ! am\nt ( deflection ( ! ne$le f ! z]o position dep5ds ^u ! /r5g? ( ! curr5t or ! voltage accord+ z ! coil is w\nd to indicate amp]es or volts4 ,illu/ration3 ,fig4 #fbj4 ,mov+ iron type in/rum5t4 ,! ess5tial p>ts are3 ,n1 s(t iron ne$le2 ,c1 coil2 ,m1 p]man5t magnet2 ,p1 po9t]2 ,s1 scale4 ,curr5t pass+ ?r\gh ! coil acts on ! ne$le1 caus+ x to turn aga9/ ! re/ra9+ =ce due to ! influ5ce ( ! p]man5t magnet4 ,illu/ration3 ,fig4 #fba4--,mov+ coil type in/rum5t4 ,! ess5tial p>ts are3 ,a1 spiral spr+2 ,c1 coil2 ,k1 s(t iron core2 ,m1 p]man5t magnet2 ,p1 po9t]2 ,s1 scale4 ,curr5t pass+ ?r\gh ! coil causes ! mov+ sy/em to turn aga9/ ! re/ra9+ =ce due to ! influ5ce ( ! p]man5t magnet4 ,ques4 ,describe a mov+ coil in/rum5t4 ,ans4 ,?is type ( in/rum5t is %[n 9 fig4 #fba4 ,x consi/s ( a mov+ coil ,c1 to :i* is atta*$ ! po9t]1 & :i* is pivot$ betwe5 ! poles ( a p]man5t magnet ,m4 ,! coil moves betwe5 ^! poles & a fix$ s(t iron core ,k1 & is held 9 ! normal position by two spiral spr+s ,a1 above & bel[ ! core4 ,! spr+s also s]ve to make electrical connection ) ! coil ,c4 ,:5 a curr5t passes ?r\gh ! coil1 magnetic l9es are set up 9 x :i* are at an angle to ^? pass+ f "o pole ( ! p]man5t magnet to ! o!r4 ,! l9es ( =ce1 :i* =m]ly pass$ f "o pole ( ! magnet to ! o!r by /raight l9es or by %ort curv$ ones1 are /ret*$ on acc\nt ( ! field produc$ by ! curr5t 9 ! coil1 &1 9 try+ to %ort5 !mselves1 t5d to twi/ ! coil ?r\gh an angle4 ,?is t5d5cy to move is resi/$ by ! two spiral spr+s1 h5ce ! coil moves until equilibrium is e/abli%$ betwe5 ! two oppos+ =ces4 ,! am\nt ( deflection ( ! po9t] dep5ds1 ei!r ^u ! curr5t /r5g?1 or ! voltage accord+ to ! w9d+ ( ! coil4 ,illu/ration3 ,fig4 #fbb4--,key/one voltmet]2 view %[+ ! mov+ elem5t be+ )drawn by loos5+ "o screw4 ,^! in/rum5ts are con/ruct$ on ! d',arsonval sy/em1 ! mov+ elem5t be+ %[n 9 detail 9 figs4 #fbc & #fbd4 ,! entire sy/em is m\nt$ ^u a solid metal base plate4 ,! p]man5t field magnet is made ( a s+le piece ( magnet /eel1 & ! pole pieces are ( s(t /eel1 p]man5tly secur$ to ! magnet 9 ord] t ! di/ribution ( ! magnetic flux w n be *ang$ by removal & replacem5t ( ! pole piece4 ,accord+ly ! mov+ me*anism is m\nt$ sep>ately f ! field1 s t x c be readily lift$ f ! field )\t remov+ ! pole pieces4 ,! function ( ! core is to secure a uni=m field4 ,! mov+ coil is w\nd ^u a =m ( alum9um1 :i* s]ves ! purpose ( damp+ by ! g5]ation ( eddy curr5ts4 ,! w9d+ ( ! coil is ( f9e copp] wire1 to :i* curr5t is convey$ by means ( ! controll+ spr+s & :i*1 9 ! case ( a voltmet]1 is connect$ 9 s]ies ) a resi/ance1 & 9 ! case ( an ammet]1 across ! t]m9als ( a %unt4 ,ques4 ,h[ does ! w9d+ diff] 9 ammet]s & voltmet]s8 ,ans4 ,an ammet] coil consi/s ( a few turns ( heavy wire 7:5 design$ to c>ry ! full curr5t71 :ile a voltmet] coil is w\nd ) _m turns ( f9e wire4 ,?us1 ! ammet] is ( l[ resi/ance1 & ! voltmet] ( high resi/ance4 ,illu/ration3 ,fig4 #fbc4--,new mov+ elem5t ( ,key/one in/rum5ts1 weight #a4b grams4 ,fig4 #fbd4--,mov+ elem5t ( ,key/one in/rum5ts assembl$ 9 be>+4 ,! mov+ elem5t consi/s ( coil1 c\nt]poise & po9t]4 ,! me*anical connections are made by means ( screws & /eady p9s4 ,9 ord] to adju/ = slight set or subset ( spr+ "u long use a z]o adju/] is provid$ by means ( :i* ?is set c be connect$ & ! po9t] br\ght back to z]o4 ,ques4 ,:y is a high resi/ance coil us$ ) a voltmet]8 ,ans4 ,z actually con/ruct$1 mo/ voltmet]s are simply special =ms ( ammet]4 ,f ,ohm's law1 ! curr5t ?r\gh a giv5 circuit equals ! pressure at its t]m9als divid$ by its resi/ance4 ,h5ce1 if a high resi/ance be connect$ 9 s]ies ) a s5sitive ammet] t w measure v small curr5ts1 !n ! curr5t pass+ ?r\gh ! circuit is directly proportional to ! voltage at its t]m9als1 & ! in/rum5t may be calibrat$ to read volts4 ,illu/ration3 ,figs4 #fbe & #fbf4--;,connections = s]ies & %unt ammet]s4 ,:5 ! con/ruction is su* t all ! curr5t passes ?r\gh ! in/rum5t1 x is connect$ z 9 fig4 #fbe1 b :]e ! in/rum5t is design$ to take only a fraction ( ! curr5t1 x is connect$ across a %unt1 z 9 fig4 #fbf1 a def9ite proportion ( ! curr5t pass+ ?r\gh ! in/rum5t & ! rema9d] ?r\gh ! %unt4 ,ques4 ,into :at two classes may ammet]s be divid$8 ,ans4 ,!y are class$ z s]ies or %unt accord+ to ! way !y are design$ to be connect$ ) ! circuit4 ,ques4 ,:at det]m9es ! mode ( connect+ ammet]s8 ,ans4 ,:5 ! wire ( ! ammet] coil is l>ge en\gh to c>ry ! :ole curr5t1 x is connect$ 9 ! circuit 9 s]ies z %[n 9 fig4 #fbe4 ,if1 h[ev]1 ! wire be small1 ! in/rum5t is connect$ 9 p>allel ) a %unt ( l[ resi/ance1 s t x only c>ries a small "p ( ! curr5t1 z 9 fig4 #fbf4 ,= circuits :i* c>ry l>ge curr5ts1 ! %unt connection is always us$1 because o!rwise ! coil ( ! ammet] w\ld h to be v heavy & ! in/rum5t correspond+ly bulky4 ,ques4 ,h[ are %unt ammet]s arrang$ to correctly measure ! curr5t8 ,ans4 ,! coil is arrang$ s t a def9ite proportion ( ! :ole curr5t passes ?r\gh x4 ,a l>ge conductor ( l[ resi/ance is connect$ directly betwe5 ! two t]m9als or b9d+ po/s ( ! in/rum5t2 ! coil is connect$ z a %unt ar\nd a def9ite "p ( ?is ma9 conductor2 !n1 s9ce ! two are connect$ 9 p>allel & ea* bran* has a def9ite resi/ance1 ! curr5t divides betwe5 ! two bran*es directly 9 proportion to _! relative conductivities1 or inv]sely accord+ to _! resi/ances4 ,! coil1 !re=e1 takes a def9ite "p ( ! :ole curr5t1 & ! =ce mov+ x & its po9t] away f ! z]o position is directly proportional to ! :ole curr5t4 ,h5ce1 by provid+ a prop] scale1 ! value ( ! entire curr5t w be indicat$4 ,illu/ration3 ,figs4 #fbg & #fbh4--,we/+h\se ammet] %unts4 ,^! %unts are us$ :]e heavy curr5ts are to be measur$4 ,! %unt is connect$ 9 s]ies ) ! bus b> or circuit to be measur$1 & its t]m9als are connect$ by means ( small leads to ! ammet] or o!r in/rum5t4 ,^! %unts are design$ to h approximately #ej millivolts drop at full rat$ curr5t4 ,!y are int5d$ prim>ily = ,we/+h\se met]s1 b c be us$ satisfactorily ) any met] requir+ #ej millivolts = full scale deflection4 ,ques4 ,h[ is a voltmet] connect$8 ,ans4 ,a voltmet] is always connect$ to ! two po9ts1 ^: diff]5ce ( pot5tial is to be measur$4 ,= in/ance1 to measure ! voltage betwe5 ! two sides ,a & ,b ( ! circuit %[n 9 fig4 #fbi1 "o t]m9al ( ! voltmet] is connect$ to wire ,a1 & ! o!r to wire ,b4 ,if ! drop or diff]5ce 9 voltage ?r\gh a c]ta9 l5g? ( wire ,l1 ( a circuit1 z f ,a to ,b 9 fig4 #fcj is to be det]m9$1 "o t]m9al ( ! voltmet] is connect$ to ,a & ! o!r to ,b4 ,9 a simil> mann] is f\nd ! drop ?r\gh a lamp4 ,illu/ration3 ,fig4 #fbi4--,voltmet] connection = measur+ ! pressure 9 an electric circuit4 ,! voltmet] is connect$ 9 p>allel 9 ! circuit at ! po9t :]e ! voltage is to be measur$4 ,fig4 #fcj4--,voltmet] connection = measur+ ! drop or fall 9 voltage 9 a c]ta9 l5g? ( wire1 z = in/ance1 ! l5g? betwe5 ! po9ts ,a & ,b4 ,! voltmet] is %unt$ betwe5 ! two po9ts ^: pressure diff]5ce is to be measur$4 ,ques4 ,:at is ! diff]5ce betwe5 a voltmet] & an ammet]8 ,ans4 ,a voltmet] measures pressure1 :ile an ammet] measures curr5t4 ,z actually con/ruct$1 mo/ voltmet]s are simply special =ms ( ammet]4 ,if a high resi/ance be connect$ 9 s]ies ) a s5sitive ammet] t w measure v small curr5ts1 !n ! curr5t pass+ ?r\gh ! circuit is directly proportional to ! pressure or voltage at its t]m9als & ! in/rum5t may be calibrat$ to read volts4 ,ques4 ,expla9 ! t]m calibrate4 ,ans4 ,to calibrate a measur+ in/rum5t is to det]m9e ! v>iations 9 its read+s by mak+ special measurem5ts1 or by comp>ison ) a /&>d4 ,illu/ration3 ,fig4 #fca4--,we/on ammet]2 view %[+ %unt enclos$ )9 ! in/rum5t4 ,we/on in/rum5ts are direct read+ & dead beat4 ,al?\gh ! scales h practically uni=m divisions1 x is n assum$ 9 ! calibration t !y are uni=m1 & ! scales are n pr9t$ or engrav$4 ,! me?od ( calibration consi/s 9 lay+ out ea* l>ge division ( ! scale by comp>+ ! in/rum5t ) a /&>d1 & !n ink+ 9 ! division l9es s f\nd4 ,! small] divisions betwe5 ! l>ge ones are !n equally spac$ & m>k$ by a me*anical me?od4 ,illu/ration3 ,fig4 #fcb4--,we/on portable voltmet]1 inspector's /yle4 ,?is in/rum5t is provid$ ) a rev]s+ key4 ,in/ead ( ! regul> b9d+ po/s1 p9s are us$ ) :i* connections are made by means ( contact cups atta*$ to flexible cords4 ,^! contact cups are conv5i5t 9 mak+ connections1 or 9 *ang+ quickly f "o range to ! o!r1 if ! in/rum5t h a d\ble scale4 ,connections = ! diff]5t ranges are made 9 precisely ! same way z ) ! regul> d\ble scale voltmet]s4 ,= ! upp] scale values1 ! contact p9 to ! "r & ! front contact p9 to ! left be+ tak51 & = ! l[] scale values1 ! left contact cup is *ang$ to ! re> contact p94 ,ques4 ,describe a sol5oid or plung] ammet]4 ,ans4 ,?is type consi/s ( a plung] or s(t iron core arrang$ to ent] a sol5oid4 ,curr5t be+ pass$ ?r\gh ! wire ( ! sol5oid causes ! core to be m or less attract$ aga9/ a re/ra9+ =ce ( gravity or spr+s4 ,a pivot$ po9t] atta*$ to ! core indicates ! curr5t value on a graduat$ dial z %[n 9 fig4 #fcc4 ,ques4 ,:at are ! objections to plung] in/rum5ts8 ,ans4 ,!y are n reliable = small read+s1 & are readily affect$ by magnetic fields4 ,illu/ration3 ,fig4 #fcc4--,plung] type in/rum5t4 ,! curr5t to be measur$ passes ?r\gh ! sol5oid1 produc+ a magnetic effect on ! s(t iron plung] :i* t5ds to draw x into ! coil1 & ?us cause ! po9t] to move ov] ! graduat$ scale4 ,! di/ance ! rod moves dep5ds on ! value ( ! re/ra9+ =ce 7:i* may be spr+s or gravity71 ! coil w9d+1 & /r5g? ( curr5t4 ,! w9d+ consi/s ( a few turns ( heavy wire = an ammet]1 & a l>ge numb] ( turns ( f9e wire :5 con/ruct$ z a voltmet]4 ,s9ce ! iron has a c]ta9 am\nt ( residual magnetism1 ! deflection ) small] foll[+ l>ge curr5ts is m ?an w\ld be produc$ by ! same curr5t foll[+ a small] "o4 ,! in/rum5t !re=e is less reliable ?an ! usual types4 ,ques4 ,describe a magnetic vane in/rum5t4 ,ans4 ,x consi/s ( a small piece ( s(t iron or vane m\nt$ on a %aft t is pivot$ a little (f ! c5t] ( a coil z %[n 9 fig4 #fcd4 ,! pr9ciple ^u :i* ! in/rum5t works is t a piece ( s(t iron plac$ 9 a magnetic field & free to move w move into su* position z to conduct ! maximum numb] ( l9es ( =ce4 ,! curr5t to be measur$ is pass$ ar\nd ! coil produc+ a magnetic field ?r\gh ! c5t] ( ! coil4 ,! magnetic field inside ! coil is /ronge/ ne> ! inn] edge1 h5ce1 ! vane w move aga9/ ! re/ra9+ =ce ( a spr+ s t ! di/ance betwe5 x & ! inn] edge ( ! coil w be z small z possible4 ,a po9t]1 atta*$ to ! vane %aft moves ov] a graduat$ dial4 ,illu/ration3 ,fig4 #fcd4--,magnetic vane in/rum5t4 ,a s(t iron vane1 ecc5trically pivot$ )9 a coil c>ry+ ! curr5t to be measur$1 is attract$ t[>d ! position :]e x w conduct ! greate/ numb] ( magnetic l9es ( =ce aga9/ ! re/ra9+ =ce ( a spr+ or equival5t4 ,ques4 ,describe an incl9$ coil in/rum5t4 ,ans4 ,z %[n 9 fig4 #fce1 a coil c>ry+ ! curr5t1 is m\nt$ at an angle to a %aft to :i* is atta*$ a po9t]4 ,a bundle ( iron /rips is m\nt$ on ! %aft4 ,a spr+ re/ra9s ! %aft & holds ! po9t] at ! z]o position :5 no curr5t is fl[+4 ,:5 a curr5t is pass$ ?r\gh ! coil1 ! iron t5ds to take up a position ) its longe/ sides p>allel to ! l9es ( =ce1 :i* results 9 ! %aft be+ rotat$ & ! po9t] mov$ on ! dial1 ! am\nt ( movem5t dep5d+ ^u ! /r5g? ( ! curr5t 9 ! coil4 ,! coils = l>ge sizes are g5]ally w\nd ) a few turns ( flat insulat$ copp] ribbon4 ,! in/rum5ts are adapt$ to ei!r direct or alt]nat+ curr5ts b are recomm5d$ = alt]nat+ curr5ts4 ,illu/ration3 ,fig4 #fce4--,?ompson incl9$ coil ammet]4 ,x is con/ruct$ on ! magnetic vane pr9ciple 9 :i* an iron vane is attract$ by ! magnetic field due to ! coil1 s z to turn itself p>allel ) ! axis ( ! coil1 ! latt] be+ incl9$ ) respect to ! axis ( ! vane4 ,! voltmet] ( ?is type has a simil>ly plac$ /ation>y coil1 b 9 place ( ! iron vane1 is provid$ ) a mov+ coil 9 s]ies ) ! o!r coil4 ,! re/ra9+ =ce 9 ea* case be+ t due to spr+s4 ,figs4 #fcf & #fcg %[ ! actual con/ruction ( incl9$ coil in/rum5ts4 ,illu/ration3 ,figs4 #fcf & #fcg4--,?ompson incl9$ coil portable indicat+ in/rum5ts4 ,fig4 #fcf1 ammet] type ,p int]ior2 fig4 #fcg1 wattmet]1 type ,p1 int]ior4 ,^! in/rum5ts1 ?\gh prim>ily design$ = use on alt]nat+ curr5t circuits1 may also be us$ on direct curr5t circuits1 by mak+ rev]s$ read+s & tak+ ! mean z ! true indication4 ,! voltmet]s & wattmet]s are con/ruct$ on ! dynamomet] pr9ciple & ! ammet]s1 on ! magnetic vane pr9ciple4 ,! voltmet]s & wattmet]s are provid$ ) a contact key :i* may be lock$ 9 position1 enabl+ ! in/rum5ts to be left con/antly 9 circuit4 ,! movem5ts ( ! po9t] are damp$ by means ( an air vane2 !re is also a friction damp+ device op]at$ by a small button to *eck excessive oscillations ( ! po9t]4 ,! incl9$ coil in/rum5ts are s design$ t ! torque is suffici5tly high to insure ! po9t] assum+ a def9ite position ) ea* *ange 9 curr5t value4 ,ques4 ,:at is ! pr9ciple ( ! hot wire in/rum5t8 ,ans4 ,its action dep5ds ^u ! heat+ ( a conductor by ! curr5t fl[+ ?r\gh x1 caus+ x to exp& & move an index ne$le or po9t]1 ! movem5ts ( :i*1 by calibration1 are made to correspond to ! pressure diff]5ces produc+ ! actuat+ curr5ts4 ,ques4 ,:at are ! *>act]i/ics ( hot wire in/rum5ts8 ,ans4 ,voltmet]s ( ?is type are n affect$ by magnetic fields1 & z _! self-induction is small1 !y c be us$ on ei!r direct or alt]nat+ curr5ts2 b !y possess c]ta9 s]i\s defects3 !y consume m curr5t ?an ! o!r types2 _c be con/ruct$ = small read+s2 are liable to burn out on accid5tal ov]loads2 & are some:at vague 9 ! read+s ne> ! z]o po9t & are sometimes inaccurate 9 ! upp] "p ( ! scale4 ,ques4 ,describe ! con/ruction & op]ation ( ! ,:itney hot wire in/rum5ts4 ,ans4 ,z %[n 9 fig4 #fch1 a wire ,,ax1 ( non-oxidizable metal1 ( high resi/ance & l[ temp]ature coeffici5t1 passes ov] a pulley ,b m\nt$ on ! %aft ,c4 ,! ends ( ! wire are atta*$ to ! plate ,e at its ends ,f & ,g1 ! wire be+ insulat$ f ! plate at ,g4 ,a spr+ ,h holds ! wire 9 t5sion & takes up ! slack due to ! expansion caus$ by ! heat+ ( ! wire :5 a curr5t passes ?r\gh x4 ,! curr5t fl[s only 9 ! portion ( ! wire m>k$ ,a1 betwe5 ! plate ,e & ! pulley ,b up to ! po9t ,k :]e ! connection is %[n4 ,:5 a curr5t fl[s ?r\gh ! wire ,a1 ! spr+ takes up ! slack1 pulls ,a ar\nd ,b1 & causes ,b to rotate ^u its %aft ,c4 ,x is cle>1 t a po9t] atta*$ to ,c1 w\ld indicate on a scale ! movem5t ( ,b & ,c1 b z ?is movem5t is v slight1 a magnify+ device w be requir$4 ,?is device consi/s ( a =k$ rod ,l1 rigidly atta*$ to ! %aft ,c1 & c>ry+ at its l[] end a silk fibre fa/5$ to ! =k & pass+ ar\nd a pulley ,m1 to :i* a po9t] ,n is atta*$4 ,= direct curr5t measurem5ts only an electromagnetic sy/em is us$4 ,illu/ration3 ,fig4 #fch4--;,diagram %[+ pr9ciple & con/ruction ( ! ,:itney hot wire in/rum5ts4 ,! action ( in/rum5ts ( ?is type dep5ds on ! heat+ ( a wire by ! passage ( a curr5t caus+ ! wire to l5g!n4 ,?is elongation is magnifi$ by suitable me*anism & transmitt$ to ! po9t] ( ! in/rum5t4 ,ques4 ,:at is ! pr9ciple ( electro/atic in/rum5ts8 ,ans4 ,! action ( ^! in/rum5ts dep5ds ^u ! fact t two conductors attract "o ano!r :5 any diff]5ce ( electric pressure exi/s betwe5 !m4 ,if "o be delicately susp5d$ s z to be free to move1 x w approa* ! o!r4 ,illu/ration3 ,fig4 #fci4--,kelv9 electro/atic voltmet]2 a =m ( in/rum5t design$ = measur+ high pressures up to #bjj1jjj volts4 ,! in/rum5t1 z illu/rat$1 consi/s ( fix$ & movable vanes ) t]m9als connect+ ) ea*4 ,^! vanes :i* act z cond5s]s take *>ges proportional to ! pot5tial diff]5ce betwe5 !m1 result+ 9 a c]ta9 attraction :i* t5ds to rotate ! movable disc aga9/ ! re/ra9+ =ce ( gravity4 ,9 ! figure aa & b are two fix$ vanes & c a movable vane1 c>ry+ a po9t] & hav+ a prop] weight at its l[] end4 ,ques4 ,describe ! ,kelv9 electro/atic voltmet]4 ,ans4 ,a simple =m consi/s1 z %[n 9 fig4 #fci1 ( a metal case conta9+ a pair ( highly insulat$ plates1 betwe5 :i* a delicately m\nt$ paddle %ap$ ne$le is free to move4 ,:5 ! ne$le is connect$ to "o side ( a circuit & ! /ation>y plates to ! o!r side1 ! ne$le is attract$ & moves betwe5 !m z indicat$ by ! po9t]4 ,adju/+ screws at ! l[] end ( ! ne$le all[ x to be balanc$ s t its c5t] ( gravity is some:at bel[ ! c5t] ( susp5sion4 ,gravity !n is ! re/ra9+ =ce4 ,! range ( ! in/rum5t may be *ang$ by hang+ diff]5t weights ^u ! ne$le4 ,by increas+ ! numb] ( blades ! in/rum5t c be made to measure z l[ z #cj volts4 ,! =m hav+ two /ation>y blades & "o movable blade is suitable = measur+ f #bjj to #bj1jjj volts4 ,! quadrant electromet] or laboratory =m w measure a fraction ( a volt4 ,illu/ration3 ,fig4 #fdj4--,?ompson a/atic in/rum5t )\t cov]4 ,:5 curr5t passes ?r\gh ! coils ( ! mov+ elem5t1 ! l9es ( =ce p>allel to ! %aft produce a torque :i* t5ds to turn ! %aft & cause ! ne$le to travel across ! scale4 ,?is action is1 ( c\rse1 oppos$ by ! magnetic field at "r angles to ! %aft act+ on ! two pieces ( magnetic metal4 ,^! a/atic in/rum5ts h no controll+ spr+s4 ,! two small silv] spirals :i* conduct ! curr5t to & f ! armature are made ( untemp]$ silv] & ex]t no =ce z spr+s4 ,! actuat+ & re/ra9+ =ces are dep5d5t ^u ! same electromagnets4 ,! damp+ effect 9 ^! in/rum5ts is produc$ by an alum9um disc mov+ 9 a magnetic field1 & is proportional to ! squ>e ( ! magnet /r5g?4 ,ques4 ,expla9 ! con/ruction & pr9ciple ( ! ,?ompson a/atic in/rum5ts4 ,ans4 ,! fields ( ^! in/rum5ts are electromagnets w\nd = any specifi$ voltage & provid$ ) b9d+ po/s sep>ate f ! curr5t po/s ( ! in/rum5t4 ,! mov+ coils are m\nt$ ^u an alum9um disc & are locat$ 9 a magnetic field :i* is p>allel to ! %aft & a/atically arrang$4 ,two small pieces ( magnetic metal are rigidly m\nt$ on ! %aft & ! a/atic compon5ts ( ! magnetic field1 :i* are p]p5dicul> to ! %aft1 t5d to keep ! pieces ( magnetic metal 9 _! initial positions4 ,:5 curr5t passes ?r\gh ! coils ( ! mov+ elem5t1 ! l9es ( =ce p>allel to ! %aft produce a torque :i* t5ds to turn ! %aft & cause ! ne$le to travel across ! scale4 ,?is action is1 ( c\rse1 oppos$ by ! magnetic field at "r angles to ! %aft act+ on ! two pieces ( magnetic metal4 ,!re are ?us no re/ra9+ spr+s1 curr5t be+ convey$ to ! mov+ coil by torsionless spirals ( silv] wire4 ,?ompson a/atic in/rum5ts c be provid$ ) pol>ity indicators1 a r$ disc %[+ on ! scale c>d :]e ! poles are rev]s$4 ,! effect ( ext]nal fields is elim9at$ by ! a/atic arrangem5t ( ! fields & ! mov+ p>ts4 ,a field :i* t5ds to increase ! torque on "o side ( ! armature dim9i%es x to a correspond+ degree on ! o!r side4 ,! damp+ effect 9 ^! in/rum5ts is produc$ by an alum9um disc mov+ 9 a magnetic field4 ,illu/ration3 ,fig4 #fda to #fdb4--,multipli]s = ,we/]n /&>d portable voltmet]s4 ,multipli]s are resi/ance boxes1 ! coils 9 :i* are highly insulat$1 & are adju/$ s t ! read+s ( ! in/rum5t may be multipli$ by any desir$ con/ant4 ,multipli]s are usually con/ruct$ s t ! indications ( ! po9t]1 multipli$ by #b1 #e1 #aj1 #bj or #ej1 w give ! voltage ( ! circuit4 ,by ! use ( multipli]s ! range ( voltmet]s may be increas$ to any practical limit4 ,illu/ration3 ,fig4 #fdc4--,portable multipli] = portable voltmet]4 ,a multipli] is us$ = increas+ ! read+s ( voltmet]s1 & consi/s ( resi/ance coils plac$ 9 a portable case4 ,a multipli] is connect$ 9 s]ies ) ! voltmet] & mu/ be adju/$ = ! in/rum5t ) :i* x is to be us$1 because ! resi/ance coil mu/ be a multiple ( ! voltmet] resi/ance4 ,= in/ance1 a multipli] ) a value ( #aj1 us$ ) a #f volt voltmet] or #eba ohms w\ld measure ab\t #e1bae ohms2 "o ) a value ( #dj1 w\ld equal ab\t #bj1hfj ohms4 ,! multipli] #aj w\ld give a total scale value ( #fj1 & ! multipli] #dj1 a total scale value ( #bdj volts to ! #f volt in/rum5t4 ,a multipli] is ( consid]able value 9 t x does away ) ! necessity ( hav+ a numb] ( voltmet]s ( diff]5t ranges4 ,! in/rum5t "h illu/rat$ has a range ( #aej volts4 ,ques4 ,:at are multipli]s8 ,ans4 ,^! are extra resi/ance coils :i* are connect$ 9 s]ies ) a voltmet] = increas+ its capacity or read+s4 ,!y are put up 9 portable boxes1 & mu/ be adju/$ = ea* p>ticul> voltmet] z ! resi/ance ( a multipli] coil mu/ be a multiple ( ! resi/ance ( ! voltmet] itself4 ,ques4 ,:at is an electro-dynamomet]8 ,ans4 ,an in/rum5t = measur+ amp]es1 volts1 or watts by ! reaction betwe5 two coils :5 ! curr5t to be measur$ is pass$ ?r\gh !m4 ,"o ( ! coils is fix$ & ! o!r movable4 ,illu/ration3 ,figs4 #fdd to #fde4--,we/]n /&>d portable %unts4 ,! milli-voltmet]s us$ 9 connection ) ^! %unts read directly 9 amp]es4 ,%unts ( diff]5t capacities c be adju/$ to ! same in/rum5t1 & x c1 !re=e1 be us$ to measure a curr5t ( #b1jjj amp]es ) ! same degree ( accuracy z a curr5t ( #a amp]e4 ,9 select+ %unts ( diff]5t capacities = use 9 connection ) "o in/rum5t x %\ld be consid]$ t ! high] ranges mu/ be ev5 multiples ( ! l[] "o 9 ord] to suit ! same scale on ! in/rum5t4 ,ques4 ,describe ! ,siem5s' electro-dynamomet]4 ,ans4 ,! ess5tial p>ts are %[n 9 fig4 #fdf4 ,! fix$ coil ,a1 compos$ ( a numb] ( turns ( wire is fa/5$ to a v]tical support1 & surr\nd$ by ! movable coil ,b ( a few turns1 or (t5 ( only "o turn4 ,! movable coil is susp5d$ by a ?read & a spiral spr+ ,c1 bel[ ! dials :i* are fa/5$ at "o end to ! movable coil & at ! o!r end to a mill$ head$ screw ,d1 :i* c be turn$ s z to place ! planes ( ! coil at "r angles to ea* o!r1 & to apply torsion to ! spr+ to oppose ! deflection ( ! movable coil = ?is position :5 a curr5t is pass$ ?r\gh ! coils4 ,! ends ( ! movable coil dip into two cups ( m]cury ,e1 ,e'1 locat$ "o above ! o!r & along ! axis ( ! coils s z to br+ ! two 9 s]ies :5 connect$ to an ext]nal circuit4 ,! arr[s %[ ! direction ( curr5t ?r\gh ! two coils4 ,an index po9t] ,f is atta*$ to ! movable coil4 ,! upp] end ( ?is po9t] is b5t at a "r angle1 s t x sw+s ov] ! dial betwe5 two /op p9s ,g1 ,g'1 & re/s directly ov] ! z]o l9e :5 ! planes ( ! coils are at "r angles to ea* o!r4 ,a po9t] ,h is atta*$ to ! torsion screw ,d1 & sweeps ov] ! scale ( ! dial4 ,! spr+ is ! controll+ factor 9 mak+ ! measurem5t4 ,illu/ration3 ,fig4 #fdf4--;,diagram ( ,siem5s' electro-dynamomet]4 ,x consi/s ( two coils on a common axis1 b set 9 planes at "r angles to ea* o!r 9 su* a way t a torque is produc$ betwe5 ! two coils :i* measures ! product ( _! curr5ts4 ,?is torque is balanc$ by twi/+ a spiral spr+ ?r\gh a measur$ angle ( su* degree t ! coils %all resume _! orig9al relative positions4 ,if ! in/rum5t be us$ = measur+ curr5t1 ! coils are connect$ 9 s]ies1 & ! read+ is !n proportional to ! squ>e ( ! curr5t4 ,if us$ z a wattmet]1 "o coil c>ries ! ma9 curr5t & ! o!r a small curr5t1 :i* is proportional to ! pressure4 ,! read+ is !n proportional to ! p[] 9 ! circuit4 ,fig4 #fdg4--;,diagram %[+ connections ( ,siem5s' electro-dynamomet] z arrang$ to read watts4 ,illu/ration3 ,figs4 #fdh to #fej4--,wright dem& indicator4 ,?is is a device = regi/]+ ! maximum amp]e dem& ( appreciable duration 9 any electrical circuit4 ,x may be us$ on ei!r direct or alt]nat+ curr5t circuits4 ,! ess5tial features & pr9ciple are z foll[s3 ,a liquid is h]metically seal$ 9 a glass vessel consi/+ ( two bulbs connect$ by a ,u tube1 & a c5tral tube call$ ! index tube1 connect$ to ! upp] end ( ! "r h& side ( ! ,u4 ,ar\nd ! left h& or heat+ bulb1 is plac$ a b& ( resi/ance metal1 ?r\gh :i* ! curr5t to be measur$ is pass$1 or a def9ite %unt$ portion ( x4 ,! heat+ effect ( ! curr5t increases ! temp]ature ( ! left h& bulb1 caus+ ! air to exp& :i* =ces ! liquid up ! "r h& side ( ! ,u tube & into ! index tube1 :]e x rema9s until ! indicator is reset4 ,! height ( ! liquid 9 ! index tube z %[n by ! scale1 indicates ! maximum curr5t :i* has pass$ ?r\gh ! indicator4 ,x is ! diff]5ce 9 temp]ature ( ! air 9 ! two bulbs :i* causes ! fl[ ( ! liquid4 ,any *ange 9 ext]nal temp]ature causes equal effect 9 bo? bulbs & !re=e does n affect ! read+4 ,illu/ration3 ,figs4 #fea & #feb4--,we/on illum9at$ dial /ation voltmet] & ammet]4 ,! voltmet] has two indices1 a po9t$ index = close read+s & an index call$ ! normal index1 :i* enables a slight deviation f ! normal voltage to be se5 f a long di/ance4 ,! normal index is inside ! case & t]m9ates 9 a circul> disc ( black5$ alum9um4 ,! disc is adju/$ f ! outside ( ! case by h&1 by means ( ! knurl$ knob se5 on ! front ( ! case1 s t x is directly bel[ ! po9t ( normal voltage4 ,:5 ! indicat+ index rea*es ! po9t ( normal voltage1 ! disc ( ! normal index appe>s 9 ! c5t] ( ! circul> op5+ ( ! indicat+ index1 a n>r[ r+ ( :ite be+ visible1 encircl+ ! disc ( ! normal index4 ,! ammet] dep5ds = its op]ation ^u ! fall ( pot5tial betwe5 two po9ts ( ! circuit c>ry+ ! ma9 curr5t1 & requires a diff]5ce ( only ab\t 4#je volt to give a full scale deflection4 ,:5 a maximum deflection is secur$1 ! curr5t pass+ ?r\gh ! in/rum5t is nev] m ?an 4#jg amp]e irrespective ( ! total capacity ( ! in/rum5t4 ,a sep>ate %unt is us$ :i* is plac$ at ! back ( ! swit*bo>d4 ,9 _m cases1 a special %unt c be disp5s$ ) & a %ort section ( ! ma9s on ! swit*bo>d1 or ! ma9s lead+ f ! dynamo1 c be us$ in/ead4 ,on ! basis ( "o squ>e in* cross section p] #a1jjj amp]es1 a l5g? ( ab\t #e feet ( copp] conductor w\ld be requir$ z a %unt1 9 :i* case h[ev]1 ?is section ( ! conductor mu/ be adju/$ ) precision4 ,ques4 ,expla9 ! op]ation ( ! ,siem5's electrodynamomet]4 ,ans4 ,9 fig4 #fdf1 :5 a curr5t is pass$ ?r\gh bo? coils1 ! movable coil is deflect$ aga9/ a /op p91 !n ! screw ,d is turn$ 9 a direction to oppose ! action ( ! curr5t until ! deflection has be5 ov]come & ! coil br\ght back to its orig9al position4 ,! angle ?r\gh :i* ! po9t] ( ! torsion screw 0 turn$ is directly proportional to ! squ>e root ( ! angle ( torsion4 ,to det]m9e ! curr5t /r5g? 9 amp]es1 ! squ>e root ( ! angle ( torsion is multipli$ by a calculat$ con/ant furni%$ by ! mak]s ( ?is in/rum5t4 ,illu/ration3 ,fig4 #fec4--,?ompson watt h\r met] 7type ,c-#f74 ,?is =m is furni%$ ) side connections1 ! l9e wires ent]+ at ! left & ! load wires at ! "r4 ,bo? sides ( ! sy/em are c>ri$ ?r\gh ! met] 9 all sizes up to & includ+ ! #ej amp]e size4 ,9 met]s ( l>g] amp]e capacities1 a voltage tap is us$4 ,ques4 ,h[ is ! electrodynamomet] adapt$ to measure volts or watts8 ,ans4 ,:5 con/ruct$ z a voltmet]1 bo? coils are w\nd ) a l>ge numb] ( turns ( f9e wire mak+ ! in/rum5t s5sitive to small curr5ts4 ,!n by connect+ a high resi/ance 9 s]ies ) ! in/rum5t x c be connect$ across ! t]m9als ( a circuit ^: voltage is to be measur$4 ,:5 con/ruct$ z a wattmet]1 "o coil is w\nd s z to c>ry ! ma9 curr5t1 & ! o!r made ) _m turns ( f9e wire ( high resi/ance suitable = connect+ across ! circuit4 ,) ?is arrangem5t1 ! =ce betwe5 ! two coils w be proportional to ! product ( amp]es by volts1 h5ce1 ! in/rum5t w measure watts4 ,illu/ration3 ,fig4 #fed4--;,int]ior view ( ,?ompson watt h\r met] 7type ,c-#f74 ,capacity3 #e to #fjj amp]es1 two wire1 & #e to #cjj amp]es1 ?ree wire2 #ajj to #bej volts4 ,! met] is support$ by ?ree lugs1 ! upp] "o ( :i* is keyhol$1 & ! l[] "r h& "o slott$4 ,?is p]mits rapid & accurate levell+ z ! top screw c be ins]t$ & ! met] hung !reon approximately level4 ,! "r h& screw may !n be plac$ 9 position & ! met] adju/$ z may be requir$ be=e =c+ ! screw home4 ,ques4 ,describe briefly ! con/ruction ( ! ,?ompson record+ wattmet]4 ,ans4 ,x consi/s ( f\r elem5ts3 #a1 a motor caus+ rotation2 #b1 a dynamo provid+ ! necess>y load or drag2 #c1 a regi/]+ device1 ! function ( :i* is to integrate ! in/antane\s values ( ! electrical en]gy to be measur$2 & #d1 means ( regulation = light & full load4 ,illu/ration3 ,,h[ ,,to ,,read ,a ,,met] ,fig4 #fee4--,record+ dials ( watt h\r met]1 illu/rat+ me?od ( read+ electric met]s4 ,! unit ( measurem5t ( electrical en]gy is ! watt h\r4 #a1jjj watt h\rs make or equal #a kil[att h\r4 ,"s electric met]s h #d dials1 ! extreme "r h& dial ( :i* regi/]s 9 kil[att h\rs1 :ile o!rs h #e dials1 ! extreme "r h& dial ( :i* regi/]s 9 t5?s ( kil[att h\rs4 ,9 mak+ out bills to cu/om]s ! extreme "r h& dial ( a #e dial met] is ignor$ 9 ord] t ! /ate ( met] %[n on bills uni=mly requires ! addition ( #c ciph]s to correctly express ! regi/ration 9 watt h\rs4 ,ea* division on ! "r h& dial 7ignor+ ! #e? dial m5tion$7 d5otes #a1jjj watt h\rs or #a kil[att h\r2 on ! next dial #aj kil[att h\rs1 on ! next dial #ajj kil[att h\rs & on ! left h& dial #a1jjj kil[att h\rs4 ,"o complete revolution ( any dial causes ! h& on ! dial imm$iately to its left to move =w>d "o division4 ,to take a /atem5t f ! met] beg9 at ! left & set d[n = ea* dial ! l[] figure next to ea* h&1 n necess>ily ! figure ne>] ! h&4 ,9 ! above example ! /atem5t is #a1gbf kil[att h\rs or #a1gbf1jjj watt h\rs4 ,subtract ! previ\s /atem5t to arrive at regi/ration = a giv5 p]iod4 ,"s met]s are subject to a multiply+ con/ant s /at$ on _! face & ! regi/ration ( su* met]s mu/ be multipli$ by ! con/ant z %[n1 to det]m9e ! actual consumption ( electrical en]gy4 ,! con/ant is ! measure ( ! me*anical adju/m5t 9 ! regi/] ( ! met] & is ! ratio betwe5 ! regi/ration ( ! dial h&s & ! true consumption4 ,?is adju/m5t is made always by ! manufactur] ( ! met] & is nev] *ang$ 9 s]vice4 ,ques4 ,:at is ! action ( ! motor 9 ! ,?ompson watt h\r met]8 ,ans4 ,x rotates at v sl[ spe$1 & s9ce !re is no iron 9 its fields & armature1 x has v little rev]se voltage4 ,its armature curr5t1 !re=e1 is indep5d5t ( ! spe$ ( rotation1 & is con/ant = any def9ite voltage appli$ at its t]m9als4 ,illu/ration3 ,fig4 #fef4--;,int]ior ( ,?ompson watt h\r met] 7type ,c-#f7 %[+ armature1 small commutator & gravity bru%es4 ,a sph]ical armature mov+ )9 circul> field coils is ! con/ruction adopt$ 9 ?is met]4 ,! armature is w\nd on a v ?9 pap] %ell1 /iff en\gh to )/& ! /ra9 due to w9d+ & subsequ5t h&l+4 ,! wire compos+ ! armature is ( ! smalle/ gauge consi/5t ) me*anical /r5g?4 ,! field coils1 z be=e /at$1 are circul>1 & are plac$ z ne> ea* o!r z possible1 "o on ei!r side ( ! armature1 ) ! int]nal diamet] j suffici5t to give ! necess>y cle>ance = ! rotat+ elem5t4 ,?is con/ruction prev5ts magnetic leakage4 ,ribbon wire is employ$ = ! field coils1 ?us economiz+ space & fur!r c>ry+ out ! idea ( conc5tration4 ,! torque ( ?is motor be+ proportion$ to ! product ( its armature & field curr5ts1 mu/ v>y directly z ! en]gy pass+ ?r\gh its coils4 ,9 ord] !n1 t ! motor %all record correctly x is necess>y only to provide "s means = mak+ ! spe$ proportional to ! torque4 ,?is is accompli%$ by apply+ a load or drag1 ! /r5g? ( :i* v>ies directly z ! spe$4 ,ques4 ,expla9 ! op]ation ( ! ,?ompson record+ wattmet]4 ,ans4 ,!re be+ no iron 9 ei!r field or armature ( ! motor elem5t1 no consid]ations ( saturation are involv$4 ,! torque or pull ( ! armature is dep5d5t ^u ! product ( ! field & armature /r5g?4 ,! /r5g? ( ! field--!re be+ no iron--v>ies directly ) ! curr5t 9 ! field4 ,?us ! /r5g? ( ! field ) #aj amp]es fl[+ to ! load is exactly twice ! /r5g? ( ! field ) #e amp]es fl[+ to ! load4 ,! /r5g? ( ! armature is dep5d5t on ! voltage ( ! sy/em to :i* x is connect$1 ! armature elem5t ( ! met] be+ practically a voltmet]4 ,!re is1 !re=e1 a torque or pull v>y+ directly ) ! /r5g? ( ! armature multipli$ by ! /r5g? ( ! field1 or1 9 o!r words1 v>y+ directly ) ! watt load1 & except 9 s f> z influ5c$ by friction1 ! spe$ ( rotation v>ies directly ) ! torque or pull4 ,! curr5ts g5]at$ 9 ! disc armature consi/ ( eddy curr5ts1 :i* circulate )9 ! mass ( ! disc4 ,in/allation ( ,wattmet]s4--,! v>i\s types ( wattmet] diff] s widely ei!r 9 me*anical details1 or op]at+ pr9ciples1 t x is cu/om>y = manufactur]s to furni% detail$ in/ructions = ! in/allation ( _! met]s4 ,su* in/ructions %\ld be c>efully foll[$ 9 all cases1 b ! foll[+ w be f\nd g5]ally applicable to all types ( motor met]3 #a4 ,aft] unpack+ ! met]1 & be=e op5+ ! case or cov]1 clean ! latt] c>efully to remove all adh]+ p>ticles ( du/ & excelsior4 #b4 ,! prop] location = ! met] %\ld be "o :]e !re is no vibration4 ,:5 ?is location has be5 select$1 nail or screw ^u ! walls1 a bo>d some:at l>g] ?an ! dim5sions ( ! back ( ! met]1 & ^u ?is bo>d hang ! met] by ! top hang]4 #c4 ,aft] hang+ ! met]1 op5 or remove ! case or cov]1 & if necess>y1 put ! me*anism 9 ord] accord+ to in/ructions furni%$ by ! manufactur]4 #d4 ,9 ord] to op]ate satisfactorily1 ! met] %\ld hang plumb1 s t ! sp9dle ( ! revolv+ elem5t w be v]tical1 & ! horizontal planes ?r\gh ! armature & ret>d+ disc w be level4 ,_m compla9ts relative to met]s be+ sl[ on light loads1 are inv>iably due to ! fact t ! met]s h be5 in/all$ out ( plumb,b4 #e4 ,9 mak+ ! circuit connections1 be v c>eful t ! positive lead or wire is plac$ 9 ! positive b9d+ po/ ( ! met]4 ,?is precaution is ess5tial = insur+ an accurate & s5sitive measurem5t on small loads4 #f4 ,:5 a met] ( ! commutat$ motor type sp>ks at ! bru%es at />t+1 x is an indication t ! commutator is du/y4 ,clean x ) a piece ( closely wov5 cotton tape #a_/d-;in* 9 wid?4 #g4 ,met]s %\ld nev] be all[$ to rema9 ) _! cov]s (f1 9 ! te/+ room1 /ation1 or any o!r place4 ,9 ord] to get ! be/ s]vice1 & to give !m long life !y mu/ be kept clean4 ,b ,,note4--,! mo/ practical & accurate me?od ( plumb+ a met] is to level x by means ( a small brass weight plac$ ^u ! ret>d+ disc4 ,place ! weight ^u ! front or back upp] surface ( ! disc1 close to ! edge4 ,if ! disc & weight rotate t[>d ! "r1 move ! bottom ( ! met] 9 ! same direction s z to raise ! disc on ! "r4 ,:5 ! disc is level1 ! weight & disc w rema9 /ation>y :5 ! weight is plac$ on ei!r ! front or ! back ( ! disc4 ,next1 place ! weight on ! disc close to ! edge on ei!r side4 ,if ! disc rotate t[>ds ! front1 sw+ ! bottom ( ! met] away f ! wall or bo>d until ! disc rema9s /ation>y :5 ! weight is plac$ ^u x on ei!r side4 ,if ! disc rotate t[>d ! back1 raise x up on t side by br++ ! top ( ! met] away f ! wall or bo>d4 ,x is possible t ! second levell+ op]ation w alt] ! position ( ! disc obta9$ by ! fir/ op]ation1 !re=e1 ! fir/ %\ld be repeat$1 & aft] t ! second also1 until ! disc rema9s /ation>y :5 ! weight is plac$ at any po9t ^u its surface4 ,?is me?od ( levell+ is m reliable ?an any me?od 9 :i* a _s level is employ$4 ,illu/ration3 ,fig4 #feg4--;,int]ior view ( ,?ompson watt h\r met] 7type ,,cq74 ,! capacities ( ?is type range f #ej to #djj amp]es inclusive1 two wire1 & #ej to #bjj amp]es inclusive1 ?ree wire1 & = voltages ( f #ajj to #fjj volts4 ,^! met]s are made ) ei!r front or back connections4 ,9 front connect$ met]s ! positions ( ! lead+-9 wires & cables are ! same z 9 ! type ,c-#f1 fig4 #fed1 s t ei!r type ( met] may be in/all$ 9 ! same location4 ,illu/ration3 ,fig4 #feh4--,specim5 record f ,g5]al ,electric record+ ammet]4 ,! record is made on a b& ( specially prep>$ pap] f\r in*es wide & sixty feet 9 l5g?4 ,on ?is pap] are rul$ l9es correspond+ to "t1 & ! in/rum5t calibration4 ,! l9es rul$ across ! pap] repres5t "t2 ^? rul$ l5g?wise repres5t volts1 amp]es1 or watts1 dep5d+ ^u ! in/rum5t con/ruction4 ,?is =m ( pap] has ! advantage ( p]mitt+ ! use ( "t divisions ( equal l5g? ?r\gh\t ! entire range ( ! record+ p54 ,! record+ p5 is atta*$ to ! mov+ elem5t 9 su* a mann] t its motion is transmitt$ 9 a /raight l9e p>allel to ! "t division on ! *>t4 ,z ! pap] is unw\nd & pass$ "u ! record+ p51 x is paid into a space at ! bottom ( ! in/rum5t case4 ,to assi/ 9 remov+ pap]1 ! in/rum5t is provid$ ) a /ripp]1 :i* enables ! pap] to be torn (f ev5ly & )\t damage4 ,! pap] fe$+ me*anism is simple4 ,by means ( suitable ge>+1 ! clock drives a drum hav+ peg tee? :i* engage ! holes locat$ ne> ! edge ( ! pap]4 ,^! tee? n only fe$ ! pap] "u ! record+ p51 b also give x a def9ite & accurate position along ! axis ( ! drum4 ,! fe$+ drum is driv5 by a friction clut*4 ,illu/ration3 ,fig4 #fei4--,we/+h\se type ,,cw-#f watt h\r met] ) cov] (f4 ,?is met] is ( ! commutator type )\t iron 9 ! magnetic circuit4 ,! sph]ical armature is closely surr\nd$ by circul> field coils :i* provide ! %orte/ magnetic pa? & smalle/ magnetic leakage1 ?us secur+ high torque ) small consumption ( en]gy4 ,! armature w9d+ is w\nd on a holl[ sph]e ( prep>$ pap] :i* is m\ld$ 9 corrugat$ =m to secure /r5g?4 ,uni=m bru% t5sion is ma9ta9$ by gravity4 ,ea* bru% consi/s ( two small r\nd wires plac$ side by side & held aga9/ ! commutator by a small c\nt]weight ^: di/ance f ! fulcrum is adju/able4 ,! curr5t w9d+ consi/s ( two flat coils ( /rap copp]1 "o clamp$ rigidly on ei!r side ( ! c5tral m\nt+ frame :i* supports ! armature be>+s4 ,^! coils are connect$ ei!r 9 s]ies or p>allel1 dep5d+ on ! capacity4 ,9 ?ree wire met]s "o ( ! coils is connect$ 9 s]ies ) ea* side ( ! l9e4 ,! ret>d+ elem5t consi/s ( a light alum9um disc rotat+ betwe5 two pairs ( p]man5t magnets4 ,! magnets are prep>$ by a special ag+ process to insure p]man5ce4 ,full load adju/m5t is made by %ift+ ! position ( ! p]man5t magnets4 ,ample light load adju/m5t or friction comp5sation is provid$ by means ( ! movable coil1 :i* c be %ift$ horizontally or radially on loos5+ "o screw4 ,! met] regi/]s directly 9 kil[att h\rs4 ,illu/ration3 ,fig4 #ffj4--;,int]ior ( ,?ompson prepaym5t watt h\r met]4 ,! actuat+ =ce is a l>ge flat coil spr+ enclos$ 9 a b>rel or drum to :i* its outside end is atta*$4 ,! op]at+ knob w9ds ?is ma9 spr+ by turn+ ! drum4 ,! spr+ has _m turns & z ! op]ation ( ! device nev] equals "o :ole turn1 ! spr+ always ex]ts a practically con/ant =ce4 ,! rate device consi/s ( a small tra9 ( ge>s secur$ to ! front ( ! frame directly back ( ! regi/]4 ,ea* device is m>k$ ) ! price p] kw-hr4 = :i* x %\ld be us$4 ,! swit* is ( ! d\ble pole d\ble break type ) leaf contacts4 ,! co9 receptacles are plac$ at ! back ( ! met]4 ,to make an advance paym5t1 ! w9d+ knob is turn$ s t ! arr[ po9ts upw>d4 ,a qu>t] doll> is !n ins]t$ 9 ! slot & ! knob turn$ to ! "r1 ! co9 s]v+ z a key :i* op]ates ! me*anism )9 ! device1 turn+ ! regi/]+ :eel & plac+ ! co9 to ! cr$it ( ! cu/om]4 ,if ! circuit be op5 :5 ! co9 is deposit$ ! same motion ( ! knob :i* moves ! regi/]+ me*anism closes ! circuit swit* conta9$ )9 ! case4 ,! dial conta9s a scale m>k$ 9 pla9 figures ov] :i* a po9t] passes indicat+ ! numb] ( co9s rema9+ to ! cr$it ( ! depositor4 ,:5 ! fir/ co9 is deposit$ & ! knob turn$ clos+ ! ma9 swit*1 ! po9t] re/s opposite ! fir/ division on ! scale4 ,if a second co9 be deposit$ be=e ! curr5t pur*as$ ) ! fir/ co9 has be5 consum$1 a second motion ( ! knob w br+ ! po9t] opposite ! second division on ! scale4 ,twelve co9s c ?us be deposit$ consecutively1 aft] :i* ! slot is automatically clos$ & fur!r prepaym5t _c be made until ! value ( "o or m co9s has be5 consum$4 ,:5ev] en]gy to ! value ( "o co9 has be5 deliv]$ ?r\gh ! met]1 ! escapem5t is me*anically releas$ turn+ ! po9t] back "o division4 ,?is process cont9ues until all ! en]gy has be5 deliv]$ = :i* paym5t has be5 made4 ,?us ! depositor c asc]ta9 at any "t h[ mu* en]gy c be obta9$ )\t fur!r paym5t4 ,:5 all en]gy has be5 deliv]$1 ! circuit swit* is op5$ s t no m curr5t c be obta9$ until "o or m co9s h be5 deposit$4 ,! indicat+ me*anism %[s only ! numb] ( co9s :i* /& to ! cr$it ( ! cu/om]1 b1 by consult+ ! met] dial1 "o c det]m9e :at fractional "p ( ! prepaym5t next to be cancell$ rema9s to ! cr$it ( ! cu/om]4 ,a co9 or wa%] l>g] ?an ! co9 = :i* ! device is design$ _c be introduc$ into ! receiv+ slot & a small] "o w n op]ate ! device4 ,h[ to te/ a met]4--,a simple te/ = asc]ta9+ :e!r a cu/om]'s met] is fa/ or sl[,c1 may be appli$ z foll[s3 #a4 ,turn (f ! lamps & o!r p[] consum+ devices 9 ! h\se & !n note ! read+ ( ! met] dial & ! exact "t ( day2 #b4 ,turn on z quickly z possible ab\t "o-t5? ( all ! lamps 9 ! h\se & all[ !m to burn = ab\t two h\rs2 #c4 ,at ! end ( two h\rs1 turn (f ! lamps z quickly z possible & note ! read+ ( ! met] dial4 ,! diff]5ce betwe5 ! fir/ & second read+s ( ! dial w be ! indicat$ consumption ( two h\rs1 & if ?is be great] ?an ! am\nt ( p[] t ought to be consum$ by ! numb] ( lamps turn$ on1 ! met] is fa/1 b if x be less1 ! met] is sl[4 ,! be/ results obta9$ by ?is me?od are only approximations1 h[ev]1 on acc\nt ( ! v>iations 9 ! watts consum$ by ! diff]5t makes ( lamp1 ! unc]ta9ty z to ! actual voltage on ! l9e at ! "t ( ! te/1 & ! lack ( k z to ! age ( ! lamps4 ,!re=e1 if ! met] te/ )9 five p] c5t41 or d n record m nor less ?an "o-tw5tie? ( ! assum$ lamp consumption x is safe to assume t ! met] is correct z ! result ( ! te/ is n likely to be any clos] to ! tru?4 ,c ,,note4--,a met] op]ates "u m v>i$ & exact+ conditions ?an almo/ any o!r piece ( app>atus4 ,x is frequ5tly subject$ to vibration1 moi/ure & extremes ( temp]ature2 x mu/ regi/] accurately on v>y+ voltages & v>i\s wave =ms2 x mu/ op]ate = _m mon?s )\t any sup]vision or att5tion :atev]2 &1 9 spite ( all ^! conditions1 x is expect$ to regi/] ) accuracy f a few p] c5t4 ( its rat$ capacity to a #ej p] c5t4 ov]load4 ,z a met] is a type ( ma*9e1 its natural t5d5cy is to run sl[2 b occasionally1 ?r\gh accid5t1 a met] may run fa/4 ,:5 a met] runs fa/ ! consum] is pay+ a high] rate p] kil[att h\r ?an 8 contract calls =4 ,he is be+ discrim9at$ aga9/4 ,! p]iodic te/+ ( met]s is !re=e a necessity & is an indication ( ! hone/y ( int5tion ( ! manag] t[>d ! cu/om]s ( 8 company4 ,met]s controll+ a v l>ge am\nt ( rev5ue may be te/$ z (t5 z once a mon?1 :ile ! ord9>y run ( met]s %\ld be te/$ at lea/ once a ye>1 once 9 eighte5 mon?s1 or once 9 two ye>s1 ! p]iod v>y+ ) diff]5t companies1 diff]5t types & diff]5t civic requirem5ts4 ,commutator type met]s1 hav+ comp>atively heavy mov+ elem5ts ) consequ5t rapid increase 9 friction due to we> on ! jewel & be>+s1 & a commutator also increas+ 9 friction ) age1 mu/ h frequ5t & exp]t att5tion to insure _! accuracy "u all conditions4 ,ques4 ,h[ %\ld a r\gh5$ commutator be clean$ & smoo!d8 ,ans4 ,by means ( tape4 ,illu/ration3 ,fig4 #ffa4--;,int]nal connections ( ,sangamo watt h\r met] 7type ,d74 ,a1 copp] disc armature1 subm]g$ 9 m]cury2 ,b1 bridge wire betwe5 b9d+ po/s1 = ma9 load curr5t1 :5 bo? sides ( ! l9e are c>ri$ ?r\gh ! met]2 ,,ct1 comp\nd+ s]ies turns ar\nd pressure circuit magnet1 build+ up field z load increases1 to comp5sate = fall+ (f 9 spe$ o!rwise f\nd2 ,d1 alum9um damp+1 or brake disc1 controll+ spe$ ( met]2 ,e1 copp] contact e>s1 imb$d$ 9 insulat+ wall ( m]cury *amb]1 lead+ curr5t into & out f armature2 ,f1 h>dwood float on armature proportion$ to give slight lift to entire mov+ sy/em1 :5 armature & float are imm]s$ 9 m]cury2 ,h1 s(t /eel disc above p]man5t magnets1 rivet$ to f9e pit* screw work+ 9 bracket above1 s t adju/m5t ( ! disc up or d[n gives v>iation 9 damp+ effect ( p]man5t magnets1 & !re=e ( ma9 spe$4 ,k1 clamp slid] ) ?umb screw1 = obta9+ light load adju/m5t by mov+ ,k to "r or left1 z may be necess>y4 ,k spans & connects p>allel wires ( light load adju/m5t1 ,,br & ,,rr'4 ,,mm1 p[]ful p]man5t magnets1 act+ on disc ,d1 giv+ ma9 spe$ control = met]4 ,n1 high resi/ance heavy wire1 =m+ "p ( s]ies adju/m5t betwe5 armature & any %unt ) :i* met] may be us$1 to set drop ?r\gh met] correct = drop ( ! %unt4 ,p1 spirally lam9at$ s(t /eel r+1 m\ld$ 9 m]cury *amb] above ! armature space1 to act z a return = magnetic l9es ( =ce f & to en]giz+ magnet bel[4 ,r1 resi/ance c>d unit1 9 s]ies ) pressure circuit coils2 9 #aaj volt met]s "o c>d is us$1 9 #bbj volt met]s two c>ds1 or "o c>d & a !rmoc\ple4 ,,br1 small brass wire1 connect$ to +o+ end ( pressure circuit coils & =m+ ,,rr' & ! slides ,k ! light load adju/m5t4 ,,rr'1 high resi/ance wire hav+ opposite ends connect$ to e>s ,,ee by l[ resi/ance wires4 ,curr5t en]giz+ ! pressure circuit coils ,,sc passes f ,,rr' ?r\gh ,k to ,,br & !nce to ! coils1 & if ,k be ne> ! end ( ,,rr' & ,,br1 ! lea/ comp5sation is obta9$2 if ne> "r end1 maximum light load comp5sation is obta9$4 ,s1 %aft or sp9dle4 ,9 actual met] ,s is divid$1 ! l[] %aft c>ry+ armature ,a1 & ! upp] %aft damp+ disc ,d4 ,,sa1 s]ies resi/ance adju/m5t1 = sett+ met] to correct drop = %unt4 ,,sc & ,,sc'1 pressure coils connect$ 9 s]ies4 ,,tt1 b9d+ po/s at bottom ( met]4 ,y1 lam9at$ s(t /eel yoke1 c>ry+ coils ,,sc & ,,sc'1 & giv+ a p[]ful & conc5trat$ magnetic field on ! armature4 ,w1 worm1 driv+ record+ dial tra94 ,,ww1 worm :eel4 ,illu/ration3 ,fig4 #ffb4--;,int]ior view ( ,columbia watt h\r met] 7type ,d71 %[+ con/ruction & pr9cipal p>ts & connections4 ,! armature w9d+ consi/s ( ?ree coils approximately circul> 9 %ape4 ,! coils are =m w\nd1 int]lock$ ) "o ano!r & ) ! light impregnat$ fibre disc :i* s]ves z a spac] = !m4 ,! alum9um damp] disc has ! conv5tional anti-creep provision 9 ! %ape ( ! ?ree small s(t iron plugs1 m\nt$ close to ! c5tral /aff1 :i* ! illu/ration %[s4 ,^! 9 _! revolution come successively )9 ! influ5ce ( an adju/able iron screw :i* is magnetiz$ by an ext5sion f "o ( ! damp] magnets4 ,! angul> relation%ip ( ! armature w9d+s & ( ! ?ree iron plugs is su* t at ! "t t ! armature is ex]t+ a maximum torque ! magnetiz$ screw is ex]t+ ! maximum pull to hold back a giv5 plug & conv]sely :5 ! armature pull is a m9imum ! magnetic screw is attract+ a plug ) ! maximum ef=t to cause ahead rotation4 ,! irregul>ities ( torque are 9 ?is way smoo!d out4 ,! commutator has ?ree segm5ts & is made ( *emically pure silv]4 ,ea* bru% is =m$ ( a l5g? ( phosphor bronze wire b5t l a hair p9 & secur$ at its ,u end to a brass sleeve1 :i* 9 turn is secur$ to an insulat$ /ud by a set screw4 ,an ext5sion on ! sleeve c>ries a micromet] screw bru% adju/m5t4 ,! ma9 spe$ adju/m5t is secur$ by provid+ a s(t iron bridge plate1 bridg+ ov] ! extremities ( ea* magnet end & adju/able1 by means ( a set screw & lock nut1 to any desir$ di/ance !refrom4 ,?is gives a regul> micromet] means ( v>y+ ! effective magnet /r5g?4 ,int]pos$ betwe5 ! s]ies coil & ! p]man5t magnets is a heavy s(t iron %ield to gu>d ! magnets aga9/ di/urbance by %ort circuit+4 ,light load adju/m5t is obta9$ by provid+ 9 ! coil circuit a s]ies ( small resi/ance spools1 equipp$ ) p9 t]m9als1 to :i* connection c be selectively made by means ( a split bu%+ t]m9al on a flexible cord4 ,?is s]ies ( spools is /rung on a metal arbor locat$ )9 ! case4 ,illu/ration3 ,fig4 #ffc4--;,diagram %[+ int]nal connections ( ! ,duncan watt h\r met]4 ,its op]ation dep5ds ^u ! pr9ciple ( ! well kn[n electro-dynamomet]1 9 :i* ! electromagnetic action betwe5 ! curr5ts 9 ! field coils & an armature produces motion 9 ! latt]4 ,x also embodies ! o!r two necess>y watt h\r met] elem5ts requir$ = ! spe$ control & regi/ration ( ! revolutions ( ! armature1 ^! be+ embodi$ 9 ! drag magnet & disc1 & ! met] regi/] respectively4 ,! motion ( ! armature is conv]t$ into cont9u\s rotation by ! aid ( a commutator & bru%es1 ! commutator be+ connect$ to ! armature coils & c>ri$ on ! same sp9dle !re)4 ,wa/e ( ,electricity 9 ,light+4--,9 l>ge resid5ces :]e a good _m s]vants are employ$ or 9 any place :]e ! p[] consum$ is n directly "u ! sup]vision ( ! p]son :o mu/ pay ! bills1 a great deal ( wa/e usually occurs4 ,if ! met] be read be=e retir+1 ! read+ 9 ! morn+ w %[ h[ mu* en]gy 0 consum$ dur+ ! night1 :i* w %[ 9 turn h[ _m lamps 7 burn+ all night4 ,a great deal ( light c be sav$ by plac+ ! lamps s t !y w ?r[ ! light :]e x is ne$$ & by plac+ small lamps su* z #h c&le p[] & #d c&le p[] 9 places :]e n mu* light is ne$$1 su* z ba?rooms1 halls1 cell>s1 etc4 ,:5 ! lamps get old & dim !y %\ld be replac$ ) new ones1 z x co/s ab\t ! same to burn an old lamp z a new "o4 ,an old #af c&le p[] lamp :i* is v dim w give only ab\t #h c&le p[] & use ab\t z mu* curr5t z is requir$ = a new #af c&le p[]4 ,if ! dim light be light en\gh1 x %\ld be replac$ by an #h c&le p[] lamp1 :i* w n consume z mu* p[] z ! old #af c&le p[]4 ,,*apt] ,,xxix ,,op]ation ,,( ,,dynamos ,be=e ,/>t+ a ,dynamo or ,motor4--,:5 ! ma*9e has be5 securely fix$1 x %\ld be c>efully exam9$ to see t all p>ts are 9 good ord]4 ,! exam9ation %\ld be made z foll[s3 #a4 ,! field magnet circuit %\ld fir/ be inspect$ to see t none ( ! wires or connections h brok5 or h become loose1 & t ! coils are correctly connect$2 #b4 ,! caps ( ! be>+s %\ld be tak5 (f1 & ^! & ! j\rnals c>efully clean$ ( all grit & dirt4 ,!y %\ld !n be oil$1 & ! caps replac$ & screw$ up by h& only2 #c4 ,! gaps betwe5 ! out] surface ( ! armature & ! pol> faces %\ld be exam9$ 9 ord] to asc]ta9 :e!r any =eign body1 su* z a small screw or nail has lodg$ !re94 ,if su* be ! case1 x %\ld be c>efully remov$ ) a bit ( wire2 #d4 ,! gu>d plates protect+ ! armature w9d+s %\ld be remov$1 & ! w9d+s c>efully inspect$ by sl[ly rotat+ ! armature1 to see t !y are n damag$1 & t ! insulation is p]fect4 ,! armature %\ld !n be f9ally rotat$ by h& to see t x revolves freely1 & t ! be>+s are securely fix$2 #e4 ,! commutator %\ld be exam9$ to see t x is n damag$ 9 any way ?r\gh "o or m ( ! segm5ts be+ knock$ 91 or ! lugs be+ =c$ into contact ) "o ano!r2 #f4 ,! bru% hold]s & bru%es %\ld be inspect$ to see t ! =m] "w freely on ! sp9dle1 & t ! hold (f cat*es "w prop]ly1 are clean & make good contact ) ! bru% hold]s or flexible leads2 #g4 ,hav+ asc]ta9$ t ! ma*9e is n injur$ 9 any way1 & t ! armature revolves freely1 ! bru%es %\ld be adju/$4 ,9 ! subsequ5t work+ ( ! dynamo x w ( c\rse be unnecess>y to foll[ ! :ole ( ^! proce$+s e "t ! ma*9e is />t$1 z x is extremely unlikely t ! ma*9e w be damag$ f ext]nal causes :ile work+ )\t ! att5dant be+ aw>e ( ! fact4 ,adju/+ ! ,bru%es4--,! adju/m5t ( ! bru%es ^u ! commutator requires c>eful att5tion if sp>k+ is to be avoid$4 ,!re are two adju/m5ts to be made3 #a4 ,= pressure2 ,! bru%es mu/ be> aga9/ ! commutator segm5ts ) suffici5t pressure = prop] contact4 #b4 ,= lead4 ,! bru%es mu/ h ! prop] angul> advance 7positive or negative1 accord+ z ! ma*9e is a dynamo or motor7 to prev5t sp>k+4 ,ques4 ,at :at po9t on ! commutator %\ld ! bru%es be>8 ,ans4 ,! po9ts ^u ! commutator at :i* ! tips ( ! bru%es 7c>ri$ by opposite arms ( ! rock]7 be>1 %\ld be1 9 bipol> dynamos1 at opposite extremities ( a diamet]4 ,9 multipol> dynamos ! positions v>y ) ! numb] ( poles & ! nature ( ! armature w9d+4 ,ques4 ,:at provision is made to facilitate ! correct sett+ ( ! bru%es8 ,ans4 ,sett+ m>ks are usually cut 9 ! coll> ( ! commutator next to ! be>+4 ,illu/ration3 ,figs4 #ffd & #ffe4--;,diagrams illu/rat+ h[ to set bru%es4 ,"s bru% hold]s require bru%es set ) ! direction ( rotation ( ! commutator1 & o!rs1 set aga9/ ! direction ( rotation4 ,9 fig4 #ffd is %[n a bru% hold] ( ! fir/ class1 :i* mu/ always be set z indicat$ by ! arr[4 ,if set 9 ! opposite direction1 tr\ble w ensue1 z an inspection ( ! figure w %[1 because ! surface ( ! commutator & ! bru% w\ld =m a toggle jo9t1 & ! bru% w\ld t5d to dig into ! commutator & ei!r break itself or b5d ! bru% rigg+4 ,9 fig4 #ffe is %[n a bru% hold] ( ! second type4 ,?is bru% is set aga9/ ! direction ( rotation1 b an inspection ( ! cut w %[ t !re is1 9 ?is case1 no t5d5cy = ! bru% to dig into ! commutator surface4 ,ea* type ( bru% hold]1 ( :i* !re are sev]al1 %\ld be adju/$ z recomm5d$ by ! manufactur] to secure prop] work+4 ,ques4 ,h[ are ! bru%es set by ^! m>ks8 ,ans4 ,! tips ( all ! bru%es c>ri$ by "o arm ( ! rock] are set 9 correct l9e ) ! commutator segm5ts m>k$ out by "o sett+ m>k1 & ! tips ( ! bru%es c>ri$ by ! o!r arm or arms are set 9 correct l9e ) ! segm5ts m>k$ out by ! o!r m>k or m>ks4 ,if "o or m ( ! bru%es 9 a set be out ( l9e ) _! sett+ m>k1 x w be necess>y to adju/ ! bru%es up to ?is m>k by pu%+ !m out or draw+ !m back1 z may be requir$1 aft]w>ds clamp+ !m 9 position4 ,:5 adju/+ ! bru%es1 ! armature %\ld always be rotat$1 s t ! sett+ m>ks are horizontal4 ,! rock] c !n be rotat$ into position1 & ! tips ( bo? sets ( bru%es conv5i5tly adju/$ to _! m>ks4 ,9 ^? bru% hold]s provid$ ) an index or po9t] = adju/+ ! bru%es1 ! sett+ m>ks ^u ! commutator are abs5t1 l5g? ( ! po9t] be+ s proportion$ t :5 ! tips ( ! bru%es are 9 l9e ) ! extreme tips ( ! po9t]s1 ! bru%es be> ^u ! correct positions on ! commutator4 ,illu/ration3 ,fig4 #fff4--,me?od ( sold]+ cable to c>bon bru%4 ,drill a hole 9 ! end1 also 9 ! side ( ! bru%1 z %[n 9 ! sket*1 & aft] ?or\ghly t9n+ ! pig-tail1 place x 9 ! end hole & fill ! holes up ) sold] ?r\gh ! side hole4 ,ano!r me?od is to drill a hole ?r\gh ! c>bon s t ! cable w j slip ?r\gh1 c\nt]s9k ! edge ( ! hole a little1 clean ! cable ?or\ghly & pass x ?r\gh ! hole4 ,!n ) any good flux & sold]1 fill ! c\nt]sunk "p on bo? sides4 ,ques4 ,:at %\ld be done aft] adju/+ ! bru%es to _! correct positions ^u ! commutator8 ,ans4 ,_! tips or rubb+ ends %\ld be exam9$ :ile 9 position to see t !y b$ accurately on ! surface ( ! commutator4 ,9 _m in/ances x w be f\nd t ?is is n ! case1 ! bru%es sometimes be>+ ^u ! po9t or toe1 & sometimes ^u ! heel1 s t !y d n make contact ) ! commutator ?r\gh\t _! entire ?ickness & wid?4 ,! angle ( ! rubb+ ends w !re=e ne$ to be alt]$ by fil+ to make !m lie flat4 ,ques4 ,h[ is ! prop] bru% contact secur$8 ,ans4 ,:5 ! bru%es d n b$ prop]ly !y %\ld be refitt$ to secure prop] contact4 ,ques4 ,h[ is ! pressure adju/m5t made8 ,ans4 ,?is is effect$ by regulat+ ! t5sion ( ! spr+s provid$ = ! purpose ^u ! bru% hold]s4 ,ques4 ,) :at pressure %\ld ! bru%es be> aga9/ ! commutator8 ,ans4 ,! t5sion ( ! spr+s %\ld be j suffici5t to cause ! bru%es to make a light yet reliable contact ) ! commutator4 ,! contact mu/ n be too light1 o!rwise ! bru%es w vibrate1 & ?us cause sp>k+2 nor mu/ x be too heavy1 or !y w press too h>d ^u ! commutator1 gr9d+1 scor+ & we>+ away ! latt] & !mselves to an undesirable ext5t1 & moreov]1 giv+ rise to heat+ & sp>k+4 ,! correct pressure is atta9$ :5 ! bru%es collect ! full curr5t )\t sp>k+1 :ile _! pressure ^u ! commutator is j suffici5t to ov]come ord9>y vibration due to ! rotation ( ! commutator4 ,illu/ration3 ,figs4 #ffg to #ffi4--,me?od ( w9d+ cables ) m>l94 ,:5 connect+ ! fe$]s & dynamo & s]vice leads to a swit*bo>d1 ! wires are (t5 s]v$ ) m>l94 ,by s]v+ is meant to tightly wrap ! wires ( ea* set toge!r ) m>l94 ,a tool = s]v+ may be made z 9 fig4 #ffg1 us+ a piece ( oak #b ins4 wide1 #g_/h 94 ?ick & #ad ins4 long1 hav+ f\r holes drill$ ?r\gh x1 z %[n4 ,! m>l9 is pass$ ?r\gh ! holes1 comm5c+ at ! hole ne>e/ ! h&le1 ! object be+ to cause a /ra9 on ! m>l9 at ! po9t :]e x passes ar\nd ! wire1 s t ! m>l9 may be wrapp$ tightly4 ,x is necess>y to s]ve ! fir/ f\r or five in*es by h&1 pu%+ ! w9d+ into ! conduit z f> z possible4 ,?is acts z an additional protection to ! wires :]e !y leave ! conduit4 ,! s]v+ is cont9u$1 z 9 fig4 #ffh1 to )9 f\r or five in*es ( ! fir/ lug by means ( ! s]v+ tool1 pass+ ! ball ( m>l9 ar\nd ! wires ) ! s]v+ tool4 ,! wires are !n b5t 9 %ape1 z 9 fig4 #ffi4 ,to s]ve ! wires prop]ly x is necess>y to tie ! ends ( ! wires taut4 ,! wires %\ld be /raight5$ & run toge!r s z to be p>allel1 be+ b\nd ) tape at diff]5t po9ts to keep !m s4 ,:5 ! s]v+ is complete ! m>l9 %\ld be ?or\ghly pa9t$ ) a moi/ure resi/+ comp\nd4 ,! m>l9 s]v+ w /iff5 ! wires & !y c be b5t v neatly to avoid t\*+ ! bus b>s ( ! bo>d4 ,:5 pa9t$ ! m>l9 h>d5s s t x is difficult to b5d ! wires aft] ! pa9t has dri$4 ,x !n requires a /rong pressure to b5d !m4 ,! m>l9 acts z an additional insulation & me*anical protection to ! wires1 & :ile no h>m w\ld result f ! wires com+ 9 contact ) ! b>s :ile ?us protect$1 x looks bett] to b5d !m s z to avoid t\*+ ! b>s4 ,direction ( ,rotation4--,?is is sometimes a matt] ( d\bt & (t5 results 9 consid]able tr\ble4 ,z a g5]al rule1 a dynamo is int5d$ to run 9 a c]ta9 direction2 ei!r "r h&$ or left h&$ accord+ to :e!r ! armature1 :5 look$ at f ! pulley end1 revolves ) or aga9/ ! direction ( ! h&s ( a clock4 ,dynamos are usually design$ to run "r h&$1 b ! manufactur]s w make !m left h&$ if s desir$4 ,x may be necess>y to rev]se ! direction ( rotation ( a dynamo1 if ! driv+ pulley to :i* x has to be connect$ happ5 to revolve left h&$1 or if x be necess>y to br+ ! loose side ( ! belt on top ( ! pulley1 or to place ! ma*9e 9 a c]ta9 position on acc\nt ( limit$ space4 ,! direction ( rotation ( ord9>y s]ies1 %unt1 or comp\nd bipol> dynamos may be rev]s$ by simply rev]s+ ! bru%es )\t *ang+ any ( ! connections1 !n *ang+ ! po9t ( contact ( ! bru% tips #ahj4 ,9 multipol> dynamos1 a simil> *ange1 am\nt+ to #ij = a f\r pole ma*9e1 & #de = an eight pole ma*9e1 w rev]se _! direction ( rotation4 ,x w be und]/ood t "u ^! conditions1 ! orig9al direction ( ! curr5t & ! pol>ity ( ! field magnets w rema9 un*ang$4 ,?is rule does n apply to arc dynamos & o!r ma*9es1 :i* h to be run 9 a c]ta9 direction only1 9 ord] to suit _! regulat+ devices4 ,if ! direction ( curr5t g5]at$ by a dynamo be opposite to t desir$1 ! two leads %\ld be rev]s$ 9 ! t]m9als1 or ! residual magnetism %\ld be rev]s$ by a curr5t f an outside s\rce4 ,illu/ration3 ,fig4 #fgj4--,me?od ( assembl+ core discs4 ,= ?is op]ation two wood5 horses %\ld be provid$ to support ! core at a conv5i5t height1 z %[n 9 ! illu/ration4 ,/>t+ a ,dynamo4--,hav+ foll[$ ! =ego+ in/ructions1 all keys1 spann]s1 bolts1 etc41 %\ld be remov$ f ! imm$iate neighborhood ( ! ma*9e1 & ! dynamo />t$4 ,illu/ration3 ,figs4 #fga & #fgb4--,t9n+ block = electric sold]+ tool4 ,x is made ) two s(t bricks4 ,"o brick is us$ to support ! sold]+ tool1 & ! o!r to conta9 ! t9n+ mat]ial & to furni% a mat]ial :i* w keep ! copp] bit bright en\gh to receive its coat+ ( t94 ,fig4 #fga repres5ts a section ( ! t9n+ brick1 :i* is scoop$ out on top z %[n by ! l[] l9e4 ,into "o end ( ! holl[ 9 ! brick1 "s sal-ammoniac is plac$ to help t9 ! copp] bit4 ,sal-ammoniac is a natural flux = copp] & aids greatly 9 keep+ ! tool well t9n$4 ,next1 "s melt$ sold] is run into ! holl[ ( ! brick1 & la/ly en\gh res9 to fill ! cavity ne>ly to ! top4 ,:5 ! tool is n 9 use1 ! electricity is swit*$ (f & ! tool p]mitt$ to lie 9 ! res94 ,if x be desir$ to repair ! t9 coat+ a little :5 ! tool is 9 use1 ! latt] is rubb$ on ! brick bel[ ! lay] ( sold]1 & ! lay] ( res94 ,if ! tool be 9 v bad condition1 x may be pu%$ into ! sal-ammoniac once or twice & !n rubb$ 9 ! sold] aga94 ,x requires b little heat to keep ! brick & its cont5ts ready = use4 ,9 fact1 ! brick is a fair non-conductor ( heat & prev5ts ! escape ( heat f "o side ( ! tool4 ,:5 mom5t>ily n 9 use1 ! tool rema9s 9 ! sold] :i* becomes melt$ und]nea? ! lay] ( res94 ,:5 ! copp] bit becomes too hot1 x w beg9 to volatilize ! res91 ?us call+ att5tion to ?is fact1 :]eupon1 ! electricity %\ld be turn$ (f f ! tool4 ,ques4 ,h[ %\ld a dynamo be />t$8 ,ans4 ,a dynamo is usually br\ght up to spe$ ei!r by />t+ ! driv+ eng9e1 or by connect+ ! dynamo to a s\rce ( p[] already 9 motion4 ,9 ! fir/ case1 x %\ld be done by a compet5t eng9e]1 & 9 ! second case by a p]son exp]i5c$ 9 putt+ on friction clut*es to revolv+ %afts1 or 9 slipp+ on belt+ to mov+ pulleys4 ,illu/ration3 ,fig4 #fgc4--;,connections = two %unt w\nd dynamos to run 9 p>allel4 ,! positive lead ( ea* ma*9e is connect$ to ! same bus b>4 ,9 />t+1 if b "o ma*9e is to be us$1 ! dynamo is fir/ br\ght up to spe$ & ! voltage regulat$ by means ( ! rheo/at ,r & ! voltmet] ,v4 ,! ma9 swit* is !n ?r[n 94 ,! connections = ! field are tak5 (f ! dynamo leads s t ! op5+ ( ! ma9 swit* w n op5 ! field circuit & = ?is reason ! field w beg9 to build up z soon z ! ma*9e is />t$4 ,:5 b "o ( ! ma*9es is runn+1 ! idle ma*9e is br\ght up to spe$ ) ! ma9 swit* op51 & ! voltage regulat$ by means ( ! rheo/at & voltmet] until ! voltages ( ! ma*9es are ! same4 ,!n ! ma9 swit* is ?r[n 9 & ! load on ! ma*9es 7:i* is asc]ta9$ by ! ammet]s7 is equaliz$ by means ( ! rheo/ats4 ,%\ld !re be any great diff]5ce 9 voltages1 ! high] "o w run ! o!r z a motor )\t *ang+ ! direction ( rotation4 ,! field curr5t w rema9 un*ang$1 & ! armature curr5t ( ! l[ dynamo w be rev]s$1 :i* w cause x to run z a motor 9 ! same direction z x ran z a dynamo4 ,:5 dynamos fe$+ curr5t to motors are to be %ut d[n1 ! swit*es on ! motors %\ld fir/ be op5$4 ,o!rwise "s ( ! motor fuses w bl[4 ,z ! voltage goes d[n ! motors w draw m curr5t to d ! "w4 ,if a plant be %ut d[n ) ! motor swit*es 9 x w g5]ally be f\nd impossible to />t a %unt dynamo1 ! l[ resi/ance 9 ! ma9s n all[+ en\gh curr5t to fl[ ar\nd ! %unt fields to en]gize !m4 ,ques4 ,%\ld ! bru%es be rais$ out ( contact 9 />t+8 ,ans4 ,! bru%es %\ld n be 9 contact 9 />t+ if !re be any dang] ( rev]se rotation1 z might happ5 :5 ! dynamo is driv5 by a gas eng9e4 ,aside f ?is1 x is desirable t ! bru%es be 9 contact1 because !y are m easily & bett] adju/$1 & ! voltage w come up sl[ly1 s t any fault or difficulty w develop gradually & c be correct$1 or ! ma*9e /opp$ be=e any injury is done4 ,illu/ration3 ,fig4 #fgd4--;,connections = two %unt dynamos to run on ! ?ree wire sy/em4 ,! two ma*9es are connect$ 9 s]ies1 ?ree wires be+ c>ri$ f !m1 "o f ! outside pole ( ea* ma*9e & "o f ! junction ( ! two ma*9es4 ,! voltage betwe5 ! outside wires is equal to ! comb9$ voltage ( ! two ma*9es & ! voltage betwe5 ! outside & ! c5tral or neutral wire is equal to ! voltage ( ! correspond+ ma*9e4 ,if ! load on ea* side ( ! sy/em be equal1 !re w be no curr5t 9 ! neutral wire1 :ile if ! loads be unequal1 ! neutral wire w h to c>ry ! diff]5ce 9 curr5t betwe5 ! two outside wires4 ,ques4 ,h[ %\ld a s]ies ma*9e be />t$8 ,ans4 ,! ext]nal circuit %\ld be clos$1 o!rwise a clos$ circuit w n be =m$ ?r\gh ! field magnet w9d+ & ! ma*9e w n build up4 ,ques4 ,:at is und]/ood by ! t]m build up8 ,ans4 ,9 />t+1 ! gradual voltage increase to maximum4 ,illu/ration3 ,fig4 #fge4--;,connections = two comp\nd w\nd dynamos to run 9 p>allel4 ,! s]ies fields ( ! ma*9es are connect$ toge!r 9 p>allel by means ( wire leads or bus b>s1 :i* connect toge!r ! bru%es f :i* ! s]ies fields are tak54 ,?is is kn[n z ! equaliz] & is %[n by ! l9e runn+ to ! middle pole ( ! dynamo swit*4 ,by trac+ out ! s]ies circuits x w be se5 t curr5t f ! upp] bru% ( ei!r dynamo has two connections to its bus b>4 ,"o ( ^! leads ?r\gh its own field1 & ! o!r1 by means ( ! equaliz] b>1 ?r\gh ! fields ( ! o!r dynamo4 ,z long z bo? ma*9es are g5]at+ equally !re is no diff]5ce ( pressure betwe5 ! bru%es ( ei!r1 b %\ld ! voltage ( "o be l[]$1 curr5t f ! o!r w\ld fl[ ?r\gh its fields & !reby raise ! voltage1 & at ! same "t r$uce its own until bo? are equal4 ,! equaliz] may !n be call$ ^u to c>ry mu* curr5t1 b to h ! ma*9es regulate closely x %\ld be ( l[ resi/ance4 ,x may also be run z %[n by ! dott$ l9es1 b ?is w leave all ! ma*9es alive :5 any "o is g5]at+4 ,! ammet]s %\ld be connect$ z %[n4 ,if !y 7 on ! o!r side !y w\ld come "u ! influ5ce ( ! equaliz+ curr5t & w\ld indicate wrong1 ei!r too high or too l[4 ,! equaliz] swit* %\ld be clos$ a little be=e ! ma9 swit*es are clos$4 ,ques4 ,h[ %\ld a %unt or comp\nd ma*9e be />t$8 ,ans4 ,all swit*es controll+ ! ext]nal circuits %\ld be op5$1 z ! ma*9e excites be/ :5 ?is is ! case4 ,if ! ma*9e be provid$ ) a rheo/at or h& regulator & resi/ance coils1 ^! latt] %\ld all be cut out ( circuit1 or %ort circuit$1 until ! ma*9e excites1 :5 !y c be gradually cut 9 z ! voltage rises4 ,:5 ! ma*9e is giv+ ! correct voltage1 z indicat$ by ! voltmet] or pilot lamp1 ! ma*9e may be swit*$ into connection ) ! ext]nal or work+ circuits4 ,ques4 ,9 />t+ a %unt dynamo1 %\ld ! ma9 l9e swit* be clos$ be=e ! ma*9e is up to voltage or aft]8 ,ans4 ,if ! ma*9e be work+ on ! same circuit ) o!r ma*9es1 or ) a /orage batt]y1 x is1 or c\rse1 necess>y to make ! voltage ( ! ma*9e equal to t on ! l9e be=e connect+ x 9 ! circuit4 ,if ! ma*9e "w alone1 ! swit* may be clos$ ei!r be=e or aft] ! voltage comes up4 ,! load w be ?r[n on sudd5ly if ! swit* be clos$ aft] ! ma*9e has built up its voltage1 ?us caus+ a /ra9 on ! belt1 & possibly draw+ wat] ov] ! eng9e cyl9d]4 ,on ! o!r h&1 if ! swit* be clos$ be=e ! voltage ( ! ma*9e has come up1 ! load is pick$ up gradually1 b ! ma*9e may be sl[ or may ev5 refuse to pick up at all4 ,ques4 ,:y does a %unt ma*9e pick up m sl[ly if ! ma9 swit* be clos$ fir/8 ,ans4 ,because ! resi/ance ( ! ma9 l9e is s mu* less ?an t ( ! field t ! small initial voltage due to ! residual magnetism causes a mu* l>g] curr5t 9 ! armature ?an 9 ! %unt field4 ,if ?is be too l>ge1 ! cross & back magnetiz+ =ce ( ! armature weak5s ! field m ?an ! initial field curr5t /r5g!ns x1 & s ! ma*9e _c build up4 ,ques4 ,if a %unt dynamo w n pick up1 :at is likely to be ! tr\ble8 ,ans4 ,! spe$ may be too sl[2 ! resi/ance ( ! ext]nal circuit may be too small2 ! bru%es may n be 9 prop] position2 "s ( ! electrical connections 9 ! dynamo may be loose1 brok5 or improp]ly made2 ! field may h lo/ its residual magnetism4 ,illu/ration3 ,figs4 #fgf & #fgg4--;,diagrams ( gr\nd detectors4 ,fig4 #fgf1 a gr\nd detector swit* suitable = m\nt+ on a swit* bo>d4 ,! two arms pivot$ at _! upp] ends are connect$ ) an insulat+ b> ,a & make contact at _! l[] ends ) two brass /rips & a contact button1 :i* are connect$ to ! bus b>s & gr\nd1 respectively4 ,:5 ! arms are mov$ to ! left1 ! positive bus b> is connect$ to ! gr\nd ?r\gh ! voltmet] ,v4 ,9 fig4 #fgg is ano!r =m ( gr\nd detector4 ,?is is kn[n z a lamp gr\nd detector4 ,on a #aaj volt sy/em two ord9>y lamps are connect$ 9 s]ies1 :ile ! l9e connect+ ! lamps is connect$ to ! gr\nd ?r\gh a snap swit* ,s4 ,:5 curr5t is on1 ! two lamps w burn ) equal brilliancy1 b at a l[] c&le p[]4 ,:5 ! swit* ,s is clos$1 if ! two l9es be cle>1 ! brilliancy ( ! lamps w n be affect$1 b if !re be a gr\nd on ! positive side1 "o lamp w burn bright]1 ! brightness dep5d+ on ! resi/ance ( ! gr\nd4 ,if !re be a dead gr\nd1 ! lamp w burn to its full c&le p[]4 ,ques4 ,:at is ! indication t ! connections betwe5 ! field coils & armature are rev]s$8 ,ans4 ,if ! ma*9e build up :5 br\ght to full spe$1 ! connections are correct1 b if x fail to build up1 ! field coils may be improp]ly connect$4 ,illu/ration3 ,fig4 #fgh4--,me?od ( correct+ rev]s$ pol>ity 9 l>ge %unt dynamo by transpos+ ! %unt field leads1 & !n />t+ up ! ma*9e4 ,z soon z ! voltmet] regi/]s any voltage1 ! dynamo may be /opp$ & ! field leads re/or$ to _! orig9al position1 :5 x w be f\nd t ! residual magnetism 9 ! pole pieces w usually br+ ! dynamo up to its pol>ity & prop] voltage4 ,?is me?od has ! disadvantages1 ( ! unc]ta9ty z to ! ma*9e build+ up1 & t a tempor>y wire mu/ probably be run f ! swit*bo>d to "o t]m9al ( ! field circuit1 :i* is usually connect$ to a t]m9al back ( ! dynamo frame1 s t ! fl[ ( curr5t ?r\gh ! field coils may be rev]s$4 ,) dynamos hav+ lam9at$ field magnet cores ( comp>atively l[ residual magnetism1 ?is me?od may suffice1 b 9 ! case ( solid field magnetic cores x is n practical4 ,a bett] me?od is to disconnect ! %unt field leads & tempor>ily ext5d !m to "s o!r s\rce ( direct curr5t4 ,if ! curr5t be ( high] voltage ?an ! coils are design$ =1 z = in/ance #aaj volt dynamo & available curr5t #ejj volt1 caution mu/ be ex]cis$ & a suitable resi/ance be provid$ to protect ! coils4 ,a #ejj volt coil1 h[ev]1 may be suppli$ f #aaj volt circuit1 provid+ ! field w9d+ to be en]giz$ is equipp$ ) a cut (f swit* hav+ a dis*>ge resi/ance1 s t x may be us$ to close & break ! circuit :5 ! tempor>y leads h be5 connect$4 ,if ! field w9d+s be n s provid$1 a bank ( lamps or "s o!r non-inductive resi/ance mu/ be connect$ across ! leads betwe5 ! field magnet coils & ! po9t at :i* ! circuit is to be op5$ & clos$4 ,?is is to provide a pa? = ! dis*>ge ( ! induc$ electromotive =ce4 ,! circuit %\ld n rema9 clos$ m ?an a few seconds if ! full voltage c be appli$4 ,x is well1 h[ev]1 to leave ! curr5t on long en\gh to run ! ma*9e up to ab\t half spe$ & make sure1 by means ( a voltmet]1 t ! pol>ity has be5 correct$4 ,:5 ?is has be5 asc]ta9$ ! dynamo %\ld be /opp$ & ! field w9d+ leads return$ to _! prop] t]m9als4 ,!n ! voltage w be br\ght up 9 ! "r direction1 provid$ ! "w has be5 done correctly4 ,?is c be te/$ by connect+ a voltmet] across ! t]m9als ( ! armature1 or by means ( a magnetic ne$le plac$ at a %ort di/ance f "o ( ! pole pieces 9 su* a position t x does n po9t to ! nor? pole4 ,if ! field coils be improp]ly connect$1 ! curr5t due to ! initial voltage w weak5 ! field magnetism & ?us prev5t ! ma*9e build+ up1 & :5 ! field circuit is clos$ ! voltmet] read+ w be r$uc$1 or ! magnetic ne$le w be less /rongly attract$4 ,ques4 ,:at w be ! result if ! connections ( "s ( ! field coils ( a dynamo be rev]s$8 ,ans4 ,if "o-half ! numb] ( coils oppose ! o!r half1 ! field magnetism w be neutraliz$ & ! ma*9e w n build up at all2 b if "o ( ! coils be oppos$ to ! o!rs1 ! ma*9e might build up1 b ! g5]at$ voltage w be l[1 & !re w be consid]able sp>k+ at "s ( ! bru%es4 ,ques4 ,h[ may x be asc]ta9$ :i* coil is rev]s$8 ,ans4 ,9 all dynamos !re %\ld be an equal numb] ( positive & negative poles1 & 9 almo/ all ( !m ! poles %\ld be alt]nately positive & negative4 ,!re=e1 if a pocket compass be br\ght ne> ! pole pieces1 & x %[ t !re are m poles ( "o k9d ?an ! o!r1 ! indication is t "o or m ( ! coils are rev]s$1 & ! improp] sequ5ce ( alt]nation w det]m9e :i* "o is wrongly connect$4 ,ques4 ,:5 a dynamo loses its residual magnetism1 h[ c x be made to build up8 ,ans4 ,by tempor>ily magnetiz+ ! field4 ,to d ?is a curr5t is pass$ ?r\gh x f ano!r dynamo1 or f ! cells ( a small prim>y batt]y4 ,usually1 ?is w set up suffici5t initial magnetism to all[ ! ma*9e to build up4 ,! batt]y circuit %\ld be brok5 be=e ! ma*9e has built up to full voltage4 ,ques4 ,:at %\ld be done if a dynamo become rev]s$ by a rev]sal ( its field magnetism due to lightn+1 %ort circuit1 or o!rwise8 ,ans4 ,! residual magnetism %\ld be rev]s$ by a curr5t f ano!r dynamo1 or f a batt]y2 b if ?is be n conv5i5t1 ! connections betwe5 ! ma*9e & ! l9e %\ld be cross$ s t ! orig9al positive t]m9al ( ! dynamo w be connect$ to ! negative t]m9al ( ! l9e1 & vice v]sa4 ,illu/ration3 ,fig4 #fgi4--,me?od ( correct+ rev]s$ pol>ity 9 comp\nd w\nd dynamo4 ,! pol>ity may be rev]s$ )\t disconnect+ or *ang+ ! wire4 ,! figure %[s two comp\nd dynamos1 & ess5tial connections4 ,! curr5t f any ma*9e connect$ to ! equaliz] b> by its equaliz] swit* w divide1 a portion go+ ?r\gh ! s]ies field w9d+ ( ! o!r ma*9es connect$ to ! bus b>1 ! division be+ det]m9$ by ! resi/ance ( ! diff]5t sets ( coils4 ,= in/ance1 assume t ,no4 #a dynamo has _h its pol>ity rev]s$ & t ,no4 #b is runn+ connect$ to ! bus b>4 ,! me?od ( rev]s+ ! pol>ity ( ,no4 #a ma*9e is z foll[s3 ,no4 #a ma*9e %\ld be at re/ & !n make sure t ! circuit break] & negative swit* are op5 & t any o!r special connections to o!r ma*9e or /ation light+ circuits are op54 ,!n close ! positive & equaliz] swit*es1 ?us all[+ a "p ( ! curr5t f ! o!r dynamo to pass ?r\gh ! equaliz] connection & ?r\gh ! s]ies field w9d+ ( ,no4 #a ma*9e 9 ! usual direction1 :i* w magnetize ! magnetic core4 ,if ,no4 #a ma*9e be a l>ge unit & ,no4 #b a small unit1 x w be necess>y to cut out ! resi/ance ( ! %unt field circuits by means ( ! rheo/at1 if x be desir$ to ma9ta9 its bus b> voltage at its normal po9t4 ,?is w rob ! s]ies w9d+ ( any o!r ma*9es :i* may be connect$ to ! bus b>s & w l[] ! voltage slightly4 ,no4 #a ma*9e is !n br\ght up to full spe$ :5 x w be f\nd to h recov]$ its correct pol>ity4 ,! positive swit* may be readily op5$1 wat*+ ! bus b> voltage closely z x w rise :5 ! curr5t is re/rict$ aga9 to ! s]ies field w9d+ ( ! o!r ma*9es4 ,! dynamo w !n be ready to cut 9 ) ! o!r ma*9es z soon z ! voltage has be5 br\ght up to ! prop] po9t1 or x may be %ut d[n until requir$4 ,ques4 ,c a dynamo be rev]s$ by rev]s+ ! connections betwe5 ! field coils & ! armature8 ,ans4 ,no1 = if ^! connections be rev]s$1 ! ma*9e w n build up4 ,ques4 ,w a dynamo build up if x become rev]s$8 ,ans4 ,yes4 ,ques4 ,!n :at is ! objection to a rev]s$ dynamo8 ,ans4 ,s9ce ! direction ( curr5t ( a rev]s$ dynamo is also rev]s$1 s]i\s tr\ble may occur if x be attempt$ to connect x 9 p>allel1 ) o!r ma*9es n rev]s$4 ,att5tion :ile ,runn+4--,:5 a dynamo is />t$ & at "w1 x w ne$ a c]ta9 am\nt ( att5tion to keep x runn+ 9 a satisfactory & effici5t mann]4 ,! fir/ po9t to be consid]$ is ! adju/m5t ( ! bru%es4 ,if ?is be neglect$1 ! ma*9e w probably sp>k badly1 & ! commutator & bru%es w frequ5tly require refitt+ to secure good contact4 ,ques4 ,:at may be said ) respect to ! lead ( ! bru%es8 ,ans4 ,! lead 9 all good dynamos is v small1 & v>ies ) ! load & class ( ma*9e4 ,! be/ lead to give to ! bru%es c 9 all cases be f\nd by rotat+ ! rock] & bru%es 9 ei!r direction to ! "r or left ( ! neutral plane until sp>k+ comm5ces1 increas+ ) ! movem5t4 ,! position midway betwe5 ^! two po9ts is ! correct position = ! bru%es1 = at ?is position ! lea/ sp>k+ occurs1 & x is at ?is position t ! bru%es %\ld be fix$ by clamp+ ! rock]4 ,illu/ration3 ,fig4 #fhj4--,me?od ( tak+ temp]ature4 ,9 tak+ ! temp]ature ( a hot "p1 x is conv5i5t to use a !rmomet] 9 :i* ! scale ( degrees has be5 et*$ on ! /em4 ,b9d ?is to ! heat$ "p1 hav+ fir/ tak5 ! precaution to cov] ! bulb ) wa/e to prev5t ! radiation ( heat & take ! read+ :5 ! column ( m]cury has ceas$ to rise4 ,! "q :i* mo/ (t5 pres5ts itself to ! att5dant is h[ hot c ! v>i\s p>ts ( a dynamo or motor become & yet be )9 ! safe limit4 ,! degree ( heat c be det]m9$ by apply+ ! h& to ! v>i\s p>ts4 ,if ! heat be be>able x is entirely h>mless1 b if ! heat become unbe>able to ! h& = m ?an a few seconds1 ! safety limit has be5 rea*$ & ! ma*9e %\ld be /opp$ & ! fault locat$4 ,( c\rse :5 ! sold] beg9s to melt at ! commutator connections & %ellac beg9s to fry out ( ! armature & an odor ( burnt cotton beg9s to p]vade ! air1 ! safe limit has be5 f> exce$$1 & 9 mo/ cases1 z a matt] ( fact s]i\s damage is ! result4 ,to be m def9ite1 no "p ( ! dynamo or motor %\ld be all[$ to rise 9 temp]ature m ?an #hj degrees ,f4 above ! temp]ature ( ! surr\nd+ air1 except+ 9 ! case ( commutators :]e no sold] has be5 us$ to connect ! leads4 ,^! c be all[$ to rise to a /ill high] temp]ature4 ,ques4 ,h[ does ! lead v>y 9 ! diff]5t types ( dynamo8 ,ans4 ,9 s]ies dynamos giv+ a con/ant curr5t1 ! bru%es require practically no lead4 ,9 %unt & comp\nd dynamos ! lead v>ies ) ! load1 & !re=e ! bru%es mu/ be rotat$ 9 ! direction ( rotation ( ! armature ) an increase ( load1 & 9 ! opposite direction ) a decrease ( load4 ,9 cases :]e ! dynamos are subject$ to a rapidly v>y+ or fluctuat+ load1 x is ( c\rse n possible to con/antly %ift ! bru%es z ! load v>ies1 !re=e ! bru%es %\ld be fix$ 9 ! positions :]e ! lea/ sp>k+ occurs at ! mom5t ( adju/m5t4 ,if at any "t viol5t sp>k+ occur1 :i* _c be r$uc$ or suppress$ by v>y+ ! position ( ! bru%es by rotat+ ! rock]1 ! ma*9e %\ld be %ut d[n at once1 o!rwise ! commutator & bru%es are liable to be de/roy$1 or ! armature burnt up4 ,?is especially ref]s to high t5sion ma*9es4 ,ques4 ,:at %\ld be done if ! bru%es beg9 to sp>k excessively8 ,ans4 ,fir/1 look at ! ammet] to see if an excessive am\nt ( curr5t is be+ deliv]$2 second1 see if ! bru%es make good contact ) ! commutator1 & if ! latt] h a b> too high1 or too l[1 & an op5 circuit4 ,illu/ration3 ,figs4 #fha & #fhb4--,rem$ies = leakage ( oil f self-oil+ be>+s4 ,if !re be suffici5t space1 a metal r+ may be atta*$ to ! %aft z 9 fig4 #fha4 ,) ?is arrangem5t ! high spe$ ( ! %aft w c>ry ! oil outside ( ! r+ & ?r[ x (f 9 ! oil res]voir4 ,ano!r way is to ins]t a t9 apron1 z %[n 9 fig4 #fhb at ,t1 :i* w s]ve to dra9 ! oil :i* may creep along ! %aft1 & also cut (f ! draft f ! pulley :i* may suck ! oil out ( ! be>+4 ,sometimes a t9 fan is atta*$ to ! pulley1 :i* t5ds to drive ! oil back into ! be>+1 & :i* also assi/s 9 keep+ ! box cool4 ,ques4 ,:at %\ld be done if ! curr5t be excessive8 ,ans4 ,if ! curr5t exce$ ! rat$ capacity by m ?an #ej p] c5t41 & cont9ue = m ?an a few m9utes1 ! ma9 swit* %\ld be op5$1 o!rwise ! ma*9e may be s]i\sly injur$4 ,ques4 ,h[ does an excessive curr5t injure a dynamo8 ,ans4 ,by caus+ x to ov]heat :i* de/roys ! insulation ( ! armature1 commutator1 etc4 ,lubrication4--,! %aft be>+s ( dynamos may be lubricat$ by sight fe$ oil]s or oil r+s4 ,! latt] me?od is almo/ univ]sally us$4 ,an oil well is provid$ 9 ! holl[ ca/+ ( ! p$e/als z %[n 9 fig4 #gbh4 ,oil r+s revolve ) ! %aft & fe$ ! latt] ) oil1 :i* is cont9u\sly br\ght up f ! res]voir bel[4 ,! dirt settles to ! bottom & ! upp] portion ( ! oil rema9s cle> = a long p]iod1 aft] :i* x is drawn (f ?r\gh ! spigot & a fre% supply p\r$ 9 ?r\gh op5+s provid$ 9 ! top4 ,! latt] are (t5 locat$ directly ov] ! slots 9 :i* ! r+s are plac$1 s t ! be>+s c be lubricat$ directly by means ( an oil cup1 if ! r+s fail to act or ! res]voir become exhau/$4 ,illu/ration3 ,fig4 #fhc4--;,imag9ative view ( a %aft %[+ its r\gh granul> /ructure4 ,9 op]ation ^! m9ute irregul>ities int]lock & act z a ret>d+ =ce1 or frictional resi/ance4 ,h5ce1 ! necessity = lubrication--a lubricant pres5ts a ?9 int]v5+ film aga9/ :i* ! surfaces rub4 ,ques4 ,:at k9d ( oil c %\ld be us$ 9 fill+ ! res]voir1 or oil cups8 ,ans4 ,"o made ( "s non-magnetic mat]ial su* z copp]1 brass1 or z9c4 ,if iron cans be us$1 !y are liable to be attract$ by ! field magnets1 & ?us possibly cat* 9 ! armature4 ,ques4 ,:at is ! indication ( insuffici5t lubrication8 ,ans4 ,! be>+s become unduly heat$4 ,ques4 ,:at precaution %\ld be tak5 ) new dynamos8 ,ans4 ,!y are liable to heat abnormally & = ! fir/ few days !y %\ld be c>efully wat*$ & lib]ally suppli$ ) oil4 ,aft] a dynamo has be5 runn+ = a %ort "t "u full load1 its armature imp>ts a c]ta9 am\nt ( heat to ! be>+s1 a little m also to ! be>+ on ! commutator end ( %aft2 beyond ?is !re is no excuse = excessive heat+4 ,! latt] may result f v>i\s causes1 "s ( :i* are giv5 ) _! rem$ies1 z foll[s3 #a4 ,a poor quality ( oil1 dirty or gritty matt] 9 ! oil2 #b4 ,j\rnal boxes too tight2 #c4 ,r\gh j\rnals1 badly scrap$ boxes2 #d4 ,belt too tight2 #e4 ,be>+s out ( l9e2 #f4 ,ov]load$ dynamo2 #g4 ,b5t armature %aft4 ,ques4 ,:at is ! all[able degree ( heat+8 ,ans4 ,x may be tak5 z a safe rule t no "p ( a work+ dynamo %\ld h a temp]ature ( m ?an #hj ,fahr4 above t ( ! surr\nd+ air4 ,accord+ly1 if ! temp]ature ( ! eng9e room be not$ be=e apply+ ! !rmomet] to ! ma*9e1 x c at once be se5 if ! latt] be work+ at a safe temp]ature4 ,9 tak+ ! temp]ature1 ! bulb ( ! !rmomet] %\ld be wrapp$ 9 a wool5 rag4 ,! screws & nuts secur+ ! diff]5t connections & cables %\ld be exam9$ occasionally1 z !y frequ5tly "w loose ?r\gh vibration4 ,illu/ration3 ,fig4 #fhd4--;,diagram illu/rat+ =ces act+ on a dynamo armature4 ,9 ! figure ! normal field magneto-motive =ce is 9 ! direction ( ! l9e #a1 #b1 produc$ by ! field circuit ,g1 if !re 7 no curr5t 9 ! armature4 ,b z soon z ! armature curr5t fl[s1 x produces ! oppos+ =ce #c1 #d1 :i* mu/ be comb9$ ) #a1 #b to give ! result+ =ce to produce magnetism & h5ce voltage4 ,! resultant #a1 #e1 if #c1 #d be l>ge en\gh1 does n diff] mu* f ! orig9al =ce #a1 #b4 ,or1 express$ 9 a m physical way1 ! bru%es ,e1 ,f1 re/ on ! commutator & all ! turns embrac$ by twice ! angle #f1 #c1 ,f1 oppose ! fl[ ( flux ?r\gh ! armature core z well z all ! turns embrac$ by twice ! angle1 #g1 #c1 ,e4 ,! rema9+ turns di/ort ! flux1 mak+ ! pole corn]s at ,a & ,b d5s]1 & at ,c & ,d r>]4 ,s t all ! effect is to kill an increase ( flux1 or voltage4 ,?is cross magnetism t5ds also to decrease ! fl[ ( flux1 = ! extra amp]e turns requir$ to =ce ! flux ?r\gh ! d5se pole tips are great] ?an ! decreas$ amp]e turns reliev$ by ! r$uction ( flux at ! o!r pole tips2 ?is foll[s1 s9ce iron z x increases 9 magnetic d5sity requires amp]e turns great] 9 proportion ?an ! increase ( flux4 ,in/ructions = ,/opp+ ,dynamos4--,:5 %utt+ d[n a ma*9e1 ! load %\ld fir/ be gradually r$uc$1 if possible1 by eas+ d[n ! eng9e2 !n :5 ! ma*9e is supply+ little or no curr5t1 ! ma9 swit* %\ld be op5$4 ,?is r$uces ! sp>k+ at ! swit* contacts1 & prev5ts ! eng9e rac+4 ,:5 ! voltmet] almo/ indicates z]o1 ! bru%es %\ld be rais$ f contact ) ! commutator4 ,?is prev5ts ! bru%es be+ damag$ 9 ! ev5t ( ! eng9e mak+ a backw>d motion1 :i* x (t5 does1 p>ticul>ly 9 ! case ( a gas eng9e4 ,on no acc\nt1 h[ev]1 %\ld ! bru%es be rais$ f ! commutator :ile ! ma*9e is g5]at+ any consid]able voltage2 = n only is ! insulation ( ! ma*9e liable to be damag$1 b 9 ! case ( l>ge %unt dynamos1 ! p]son lift+ ! bru%es is liable to receive a viol5t %ock4 ,ques4 ,:at att5tion %\ld ! ma*9e receive aft] x has be5 %ut d[n8 ,ans4 ,x %\ld be ?or\ghly clean$4 ,any adh]+ copp] du/1 dirt1 etc41 %\ld be remov$ f ! armature by du/+ ) a /iff bru%1 & ! o!r portions ( ! ma*9e %\ld be ?or\ghly clean$ ) l95 rags4 ,wa/e %\ld n be us$1 z x is liable to leave ?reads or fluff on ! project+ p>ts ( ! ma*9e1 & on ! w9d+s ( ! armature1 :i* is difficult to remove4 ,ques4 ,:at att5tion %\ld be giv5 to ! bru%es & bru% ge>8 ,ans4 ,!y %\ld be exam9$ & ?or\ghly clean$4 ,if necess>y ! bru%es %\ld be refitt$ & readju/$4 ,all t]m9als1 screws1 bolts1 etc41 %\ld be c>efully clean$ & screw$ up ready = ! next run4 ,! bru% hold]s %\ld receive special att5tion1 z :5 dirty1 !y are liable to /ick & cause sp>k+4 ,all dirt & oil %\ld be remov$ f ! spr+s1 contacts1 pivots1 & o!r work+ p>ts4 ,x is advisable at /at$ int]vals to entirely remove ! bru% hold]s f ! rock] arms1 & give !m a ?or\gh clean+ by tak+ !m to pieces1 & clean+ ea* "p sep>ately ) em]y clo? & b5zol9e or soda solution4 ,ano!r po9t to :i* p>ticul> att5tion %\ld be giv5 is ! clean+ ( ! bru% rock]4 ,?is be+ compos$ :olly ( metal1 & ! two sets ( positive & negative bru%es be+ only sep>at$ f x by a few ?9 insulat+ wa%]s1 x foll[s t if any copp] du/ giv5 (f by ! bru%es be deposit$ 9 ! neighborhood ( ^! wa%]s1 !re is consid]able liability = a %ort circuit ( ! ma*9e to occur by ! du/ bridg+ across ! insulation4 ,ques4 ,:at fur!r att5tion %\ld be giv58 ,ans4 ,x is a good plan1 :5 ! ma*9e has be5 ?or\ghly clean$ & all connections made secure1 to occasionally te/ ! insulation ( ! diff]5t p>ts4 ,if a record be kept ( ^! te/s1 any det]ioration ( ! insulation c at once be detect$1 localiz$ & rem$i$ be=e x has become suffici5tly bad to cause a breakd[n4 ,z a means ( protect+ ! ma*9e f any moi/ure1 dirt1 etc41 :ile /&+ idle1 x is advisable to cov] x ) a suitable wat]pro( cov]4 ,,*apt] ,,xxx ,,c\pl+ ,,( ,,dynamos ,s]ies & ,p>allel ,connections4--,:5 x is necess>y to g5]ate a l>ge & v>iable am\nt ( electrical en]gy1 z mu/ be done 9 c5tral g5]at+ /ations1 ap>t f ! "q ( liability to breakd[n1 x is nei!r economical nor desirable t ! :ole ( ! en]gy %\ld be furni%$ f a s+le dynamo4 ,s9ce ! effici5cy ( a dynamo is dep5d5t ^u its output at any mom5t1 or ! load at :i* x is work$ 7! effici5cy v>y+ f ab\t #ie p] c5t4 at full load to #hj p] c5t4 at half load71 x is advisable 9 ord] to secure ! greate/ economy 9 work+1 to op]ate any dynamo z ne> full load z possible4 ,"u ! above circum/ances1 :5 ! :ole ( ! output is g5]at$ by a s+le dynamo ?is c evid5tly n be effect$1 = ! load w naturally fluctuate up & d[n dur+ ! work+ h\rs1 z ! lamps1 motors1 etc41 are swit*$ into & out ( circuit2 h5ce1 al?\gh ! dynamo may be work+ at full load dur+ a c]ta9 portion ( ! day1 at o!r times x may probably be work+ bel[ half load1 & !re=e ! effici5cy & economy 9 work+ 9 su* an arrangem5t is v l[4 ,ques4 ,h[ is maximum effici5cy secur$ ) v>iable load8 ,ans4 ,x is usual to divide up ! g5]at+ plant into a numb] ( units1 v>y+ 9 size1 s t z ! load increases1 x c ei!r be %ift$ to ma*9es ( l>g] size1 or :5 x exce$s ! capacity ( ! l>ge/ dynamo1 ! output ( "o c be add$ to t ( ano!r1 & ?us ! dynamos actually at "w at any mom5t c be op]at$ z ne>ly z possible at full load4 ,ques4 ,:at %\ld be not$ ) respect to connect+ "o dynamo to ano!r8 ,ans4 ,x is necess>y to take c]ta9 precautions 7z lat] expla9$7 9 ord] t ! o!r dynamos may n be affect$ by ! *ange1 & t !y may "w satisfactorily toge!r4 ,ques4 ,:at are ! two me?ods ( c\pl+ dynamos8 ,ans4 ,!y are connect$ 9 s]ies1 or 9 p>allel4 ,9 c\pl+ dynamos 9 s]ies1 ! curr5t capacity ( ! plant is kept at a con/ant value1 :ile ! output is increas$ 9 proportion to ! pressures ( ! ma*9es 9 circuit4 ,:5 connect$ 9 p>allel1 ! pressures ( all ! ma*9es are kept at a con/ant value1 :ile ! output ( ! plant is increas$ 9 proportion to ! curr5t capacities ( ! ma*9es 9 circuit4 ,c\pl+ ,s]ies ,dynamos 9 ,s]ies4--,s]ies w\nd dynamos w run satisfactorily toge!r )\t special precautions :5 c\pl$ 9 s]ies1 if ! connections be arrang$ z 9 fig4 #fhe4 ,! positive t]m9al ( "o dynamo is connect$ to ! negative t]m9al ( ! o!r1 & ! two out] t]m9als are connect$ directly to ! two ma9 conductors or bus b>s ?r\gh ! ammet] ,a1 fuse ,f1 & swit* ,s4 ,if x be desir$ to regulate ! pressure & output ( ! ma*9es1 v>iable resi/ances1 or h& regulators ,r1 ,r#a1 may be arrang$ z %unts to ! s]ies coils z %[n1 s z to div]t a portion or ! :ole ( ! curr5t !refrom4 ,s]ies ,dynamos 9 ,p>allel4--,simple s]ies w\nd dynamos n be+ well adapt$ = ! purpose ( ma9ta9+ a con/ant pressure1 are 9 practice seldom c\pl$ 9 p>allel2 ! conditions or work+1 h[ev]1 d]ive importance f ! fact t comp\nd dynamos1 be+ provid$ ) s]ies coils1 are subject to simil> conditions :5 work+ 9 p>allel1 :i* is frequ5tly ! case4 ,ques4 ,:at may be said ) respect to c\pl+ two or m pla9 s]ies dynamos 9 p>allel8 ,ans4 ,! same proc$ure _c be foll[$ z 9 ! case ( pla9 %unt dynamos1 = ! reason t if ! voltage ( ! dynamo to be c\pl$ be exactly equal to t ( ! bus b>s :5 connect$ 9 p>allel1 ! comb9ation w be un/able4 ,illu/ration3 ,fig4 #fhe4--;,diagram %[+ me?od ( c\pl+ s]ies dynamos 9 s]ies4 ,r & ,r' are two h& regulators :i* are plac$ 9 %unt across ! coil t]m9als to regulate ! pressure & output ( ! ma*9e4 ,ques4 ,:y is ?is8 ,ans4 ,if1 f any cause1 ! pressure at ! t]m9als ( "o ( ! dynamos fall bel[ t ( ! o!rs1 x imm$iately takes a small] proportion ( ! load2 z a consequ5ce1 ! curr5t 9 its field coils is r$uc$1 & a fur!r fall ( pressure imm$iately takes place4 ,?is aga9 causes ! dynamo to rel9qui% a portion ( its load1 & aga9 occurs a fur!r fall ( pressure4 ,?us ! process goes on1 until f9ally ! dynamo ceases to supply curr5t1 & ! curr5t f ! o!r dynamos fl[+ 9 its field coils 9 ! rev]se direction rev]ses its magnetism1 & causes x to run z a motor aga9/ ! driv+ p[] 9 ! opposite direction to t 9 :i* x previ\sly ran z a dynamo4 ,"u su* circum/ances ! armature is liable to be de/roy$ if ! fuse be n imm$iately bl[n1 & 9 any case x is subject$ to a v detrim5tal %ock4 ,?is t5d5cy to rev]se 9 s]ies dynamos c be effectually prev5t$ by connect+ ! field coils ( all ! dynamos 9 p>allel4 ,illu/ration3 ,fig4 #fhf4--;,diagram %[+ me?od ( c\pl+ s]ies dynamos 9 p>allel4 ,9 ! diagram ,a1 ,a'1 are ammet]s2 ,f1 ,f'1 fuses2 ,s1 ,s'1 swit*es4 ,ques4 ,h[ are ! field coils ( all ! dynamos connect$ 9 p>allel8 ,ans4 ,?is is effect$ 9 practice by connect+ ! ends ( all ! s]ies coils :]e !y jo9 on to ! armature circuit by a ?ird connection1 call$ ! equaliz+ connection1 or equaliz]1 z %[n 9 fig4 #fhf4 ,ques4 ,:at is ! effect ( ! equaliz]8 ,ans4 ,! imm$iate effect is to cause ! :ole ( ! curr5t g5]at$ by ! plant to be divid$ among ! s]ies coils ( ! sev]al dynamos 9 ! inv]se ratio ( _! resi/ance1 )\t any reg>d z to :e!r ?is curr5t comes f "o armature1 or is divid$ among ! :ole4 ,! fields ( ! sev]al dynamos be+ ?us ma9ta9$ con/ant1 or at any rate be+ caus$ to v>y equally1 ! t5d5cy = ! pressure ( "o dynamo to fall bel[ t ( ! o!rs is dim9i%$4 ,%unt ,dynamos 9 ,s]ies4--,! simple/ op]ation 9 connection ) ! c\pl+ ( dynamos1 & ! "o us$ probably m frequ5tly 9 practice ?an any o!r1 is ! c\pl+ ( two or m %unt dynamos to run ei!r 9 s]ies or 9 p>allel4 ,:5 connect$ 9 s]ies1 ! positive t]m9al ( "o ma*9e is jo9$ to ! negative ( ! o!r1 & ! two out] t]m9als are connect$ ?r\gh ! ammet] ,a1 fuses ,f1 ,f'1 & swit* ,s1 to ! two ma9 conductors or omnibus b>s z repres5t$ 9 fig4 #fhg4 ,! ma*9e w op]ate :5 ! connections are arrang$ 9 ?is mann]1 if ! ends ( ! %unt coils be connect$ to ! t]m9als ( _! respective ma*9es4 ,%unt ,dynamos 9 ,p>allel4--,! c\pl+ ( two or m %unt dynamos to run 9 p>allel is effect$ )\t any difficulty4 ,?is me?od ( c\pl+ dynamos is "o t is v frequ5tly us$4 ,fig4 #fhh illu/rates diagrammatically ! me?od ( arrang+ ! connections4 ,! positive & negative t]m9als ( ea* ma*9e are connect$ respectively to two massive insulat$ copp] b>s1 %[n at ! top ( ! diagram1 call$ omnibus b>s1 ?r\gh ! d\ble pole swit*es1 ,s1 ,s'1 & ! d\ble pole fuses ,f1 ,f'4 ,ammet]s1 ,a1 ,a' are ins]t$ 9 ! ma9 circuit ( ea* ma*9e1 & s]ve to indicate ! am\nt ( curr5t g5]at$ by ea*4 ,an automatic swit* or cut\t1 ,ac1 ,ac'1 is also %[n z be+ includ$ 9 ! ma9 circuit ( ea* ( ! ma*9es1 al?\gh ?is appliance is sometimes disp5s$ )4 ,! pressure ( ea* ( ! ma*9es is regulat$ indep5d5tly by means ( ! h& regulators ,r1 ,r'1 ins]t$ 9 s]ies ) ! %unt circuit4 ,! %unt circuits are repres5t$ z be+ connect$ to ! positive & negative t]m9als ( ! respective ma*9es1 b 9 _m cases :]e ! load is subject$ to sudd5 v>iations1 & :5 a l>ge numb] ( ma*9es is connect$ to ! bus b>s1 ! %unt coils are frequ5tly connect$ direct to ^!4 ,9 su* circum/ances ?is me?od is pref]able1 z by means ( x ! fields ( ! idle dynamos c be excit$ almo/ at once direct f ! bus b>s by ! curr5t f ! work+ dynamos2 h5ce1 if a heavy load come on sudd5ly1 no "t ne$ be lo/ 9 build+ up a new ma*9e previ\s to swit*+ x into p>allel4 ,! pressure ( ! lamp circuit is giv5 by a voltmet] ^: t]m9als are plac$ across ! bus b>s2 & ! pressure at ! t]m9als ( ea* ( ! ma*9es is indicat$ by sep>ate voltmet]s or pilot lamps1 ! t]m9als ( :i* are connect$ to ^? ( ! respective ma*9es4 ,illu/ration3 ,fig4 #fhg4--;,diagram %[+ me?od ( c\pl+ %unt dynamos 9 s]ies4 ,! ends ( ! %unt coils may be connect$ to ! t]m9als ( _! respective ma*9e1 or !y may be connect$ 9 s]ies z %[n4 ,ques4 ,describe a bett] me?od ( p>allel connection4 ,ans4 ,bett] results are obta9$ by connect+ bo? ! %unt coils 9 s]ies ) "o ano!r1 s t !y =m "o long %unt betwe5 ! two ma9 conductors1 ! same z 9 fig4 #fhg4 ,:5 arrang$ 9 ?is way1 ! regulation ( bo? ma*9es may be effect$ simultane\sly by ins]t+ a h& regulator 7,r7 9 s]ies ) ! %unt circuit z repres5t$4 ,illu/ration3 ,fig4 #fhh4--;,diagram %[+ me?od ( c\pl+ %unt dynamos 9 p>allel4 ,swit*+ ,dynamo ,into & ,out ( ,p>allel4--,9 ord] to put an additional dynamo 9 p>allel ) ^? already work+1 x is necess>y to run ! new dynamo up to full spe$1 &1 :5 x excites1 regulate ! pressure by means ( a h& regulator until ! voltmet] connect$ to ! t]m9als ( ! ma*9es regi/]s "o or two volts m ?an ! voltmet] connect$ to ! lamp circuit1 & !n close ! swit*4 ,! load ^u ! ma*9e c !n be adju/$ to correspond ) t ^u ! o!r ma*9es by means ( ! h& regulator4 ,ques4 ,9 connect+ a %unt dynamo to ! bus b>s1 mu/ ! voltage be c>efully adju/$8 ,ans4 ,!re is little dang] 9 ov]load+ ! armature 9 mak+ ! connection h5ce ! pressure ne$ n be accurately adju/$4 ,x is1 9 fact1 common practice 9 c5tral /ations to judge ! voltage ( ! new dynamo m]ely by ! appe>ance ( its pilot lamp4 ,ques4 ,h[ is a ma*9e cut out ( ! circuit8 ,ans4 ,:5 %utt+ d[n a ma*9e1 ! load or curr5t mu/ fir/ be r$uc$1 by gradually clos+ ! /op valve ( ! eng9e1 or ins]t+ resi/ance into ! %unt circuit by means ( ! h& regulator2 !n :5 ! ammet] indicates n9e or t5 amp]es1 ! ma9 swit* is op5$1 & ! eng9e /opp$4 ,by foll[+ ?is plan1 ! heavy sp>k+ at ! swit* contacts is avoid$1 & ! t5d5cy = ! eng9e to race1 r$uc$4 ,ques4 ,:at precaution mu/ be tak5 9 r$uc+ ! curr5t8 ,ans4 ,c>e mu/ be tak5 n to r$uce ! curr5t too mu*4 ,ques4 ,:y is ?is necess>y8 ,ans4 ,!re is dang] t ! ma*9e may receive a rev]se curr5t f ! o!r dynamos1 result+ 9 heavy sp>k+ at ! commutator1 & 9 ! ma*9e be+ driv5 z a motor4 ,ques4 ,:at provision is made to obviate ?is dang]8 ,ans4 ,dynamos t are to be run 9 p>allel are frequ5tly provid$ ) automatic cut\ts1 set s z to automatically swit* out ! ma*9e :5 ! curr5t falls bel[ a c]ta9 m9imum value4 ,divid+ ! ,load4--,if a plant1 compos$ ( %unt dynamos runn+ 9 p>allel1 be subject$ to v>iations ( load1 gradual or in/antane\s1 ! dynamos w1 if !y all h simil> *>act]i/ics1 ea* take up an equal %>e ( ! load4 ,if1 h[ev]1 z is sometimes ! case1 ! *>act]i/ics ( ! dynamos be dissimil>1 ! load w n be %>$ equally1 ! dynamos ) ! mo/ droop+ *>act]i/ics tak+ less ?an _! %>e ) an increase ( load1 & m ?an _! %>e ) a decrease ( load4 ,if ! diff]5ce be slight1 x may be readily comp5sat$ by means ( ! h& regulator increas+ or decreas+ ! pressures ( ! ma*9es1 z ! load v>ies4 ,if1 h[ev]1 ! diff]5ce be consid]able1 & ! fluctuations ( load rapid1 x becomes practically impossible to ev5ly divide ! load by ?is means4 ,"u su* circum/ances1 ! pressure at ! bus b>s is liable to great v>iations1 & !re is also liability ( bl[+ ! fuses ( ! ov]load$ dynamos1 ?us precipitat+ a g5]al breakd[n4 ,to cause an equal division ( ! load among all ! dynamos1 "u su* circum/ances1 x is ne$ful to ins]t a small resi/ance 9 ! armature circuits ( su* dynamos z possess ! /raighte/ *>act]i/ics1 or ( su* dynamos z take m ?an _! %>e ( an increase ( load4 ,by suitably adju/+ or proportion+ ! resi/ances1 ! pressures at ! t]m9als ( all ! ma*9es may be made to v>y equally "u all v>iations ( load1 & ea* ( ! ma*9es w !n take up its prop] %>e ( ! load4 ,c\pl+ ,comp\nd ,dynamos 9 ,s]ies4--,s9ce comp\nd dynamos may be reg>d$ z a comb9ation ( ! %unt & s]ies w\nd ma*9es1 & z no special difficulties are enc\nt]$ 9 runn+ ^! latt] 9 s]ies1 analogy at once leads to ! conclusion t comp\nd dynamos "u simil> circum/ances may be c\pl$ toge!r ) equal facility4 ,ques4 ,h[ are comp\nd dynamos connect$ to op]ate 9 s]ies8 ,ans4 ,! s]ies coils ( ea* are connect$ z 9 fig4 #fhe1 & ! %unt coils are connect$ z a s+le %unt z 9 fig4 #fhg1 :i* may ei!r ext5d simply across ! out] bru%es ( ! ma*9es1 s z to =m a d\ble %ort %unt1 or may be a %unt to ! bus b>s ( ext]nal circuit1 s z to =m a d\ble long %unt4 ,illu/ration3 ,fig4 #fhi4--;,c\pl+ comp\nd dynamos 9 s]ies2 %ort %unt connection4 ,! dott$ l9es indicate ! *anges t w\ld be made = long %unt connection4 ,comp\nd ,dynamos 9 ,p>allel4--,ma*9es ( ?is type w n run satisfactorily toge!r 9 p>allel unless all ! s]ies coils are connect$ toge!r by an equaliz+ connection1 z 9 s]ies dynamos4 ,! me?od ( arrang+ ! connections z adopt$ 9 practice1 be+ illu/rat$ 9 fig4 #fij4 ,by means ( x idle ma*9es are completely disconnect$ f ^? at "w4 ,ques4 ,h[ is ! equaliz] connect$8 ,ans4 ,! equaliz] is connect$ direct to ! positive bru%es ( all ! dynamos1 a ?ree pole swit* be+ fitt$ = disconnect+ x f ! circuit :5 ! ma*9e to :i* x is connect$ is n work+4 ,! two contacts ( ! swit* are respectively connect$ to ! positive & negative conductors1 :ile ! c5tral contact is connect$ to ! equaliz]4 ,illu/ration3 ,fig4 #fij4--;,diagram %[+ me?od ( c\pl+ comp\nd dynamos 9 p>allel4 ,swit*+ a ,comp\nd ,dynamo ,into & ,out ( ,p>allel4--,if ! *>act]i/ics ( all ! dynamos be simil>1 & ! connections arrang$ z 9 figs4 #fij1 or #fia1 ! only precaution to be obs]v$ 9 swit*+ a new ma*9e into p>allel is to h its voltage equal1 or ne>ly equal to t ( ! bus b>s previ\s to clos+ ! swit*4 ,if ?is be ! case1 ! new ma*9e w take up its due %>e ( ! load )\t any %ock4 ,illu/ration3 ,fig4 #fia4--;,diagram %[+ ano!r & bett] me?od ( c\pl+ comp\nd dynamos 9 p>allel4 ,) ?is arrangem5t ! idle ma*9es are completely disconnect$ f ^? at "w4 ,! same ref]5ce lett]s are common 9 bo? diagrams4 ,s1 ,s' are swit*es2 ,f1 ,f' fuses2 ,a1 ,a' ammet]s1 :i* indicate ! total am\nt ( curr5t g5]at$ by ea* ( ! ma*9es2 ,,ac1 ,,ac'1 automatic swit*es1 arrang$ = automatically swit*+ out a ma*9e 9 ! ev5t ( ! pressure at its t]m9als be+ r$uc$ ?r\gh any cause2 ,r1 ,r1' are h& regulators1 ins]t$ 9 ! %unt circuits ( ea* ( ! ma*9es1 by means ( :i* ! pressures ( ! individual ma*9es may be v>i$ & ! load ^u ea* adju/$4 ,! pressure at ! bus b>s is giv5 by ! voltmet] ,v1 "o t]m9al ( :i* is connect$ to ea* ( ! b>s2 a second voltmet] may be us$1 to give ! pressure ( any individual ma*9e1 by connect+ voltmet] keys to ! t]m9als ( ea* ( ! ma*9es1 or a sep>ate voltmet] may be us$ = ea* individual ma*9e4 ,! only ess5tial diff]5ce betwe5 figs4 #fij & #fia is1 t 9 fig4 #fij ! equaliz] is connect$ direct to ! positive bru%es ( all ! dynamos1 :ile 9 fig4 #fia ! equaliz] is br\ght up to ! swit*bo>d & arrang$ betwe5 ! two bus b>s1 a swit* be+ fitt$ = disconnect+ x f ! circuit :5 ! ma*9e to :i* x is connect$ is n work+4 ,ques4 ,h[ is a comp\nd dynamo1 runn+ 9 p>allel1 cut out ( circuit8 ,ans4 ,! load is fir/ r$uc$ to a few amp]es1 z 9 ! case ( %unt dynamos1 ei!r by eas+ d[n ! eng9e1 or by cutt+ resi/ance into ! %unt circuit by means ( ! h& regulator1 & !n op5+ ! swit*4 ,previ\s to ?is1 h[ev]1 x is advisable to increase ! voltage at ! bus b>s to a slight ext5t1 z :ile sl[+ d[n ! eng9e ! load ^u ! outgo+ dynamo is transf]r$ to ! o!r dynamo armatures1 & ! curr5t 9 _! s]ies coils n be+ increas$ 9 proportion1 ! voltage at ! bus b>s is consequ5tly r$uc$ some:at4 ,equaliz+ ! ,load4--,:5 a numb] ( comp\nd dynamos ( v>i\s output1 size1 or make1 are runn+ toge!r 9 p>allel1 x frequ5tly happ5s t all _! *>act]i/ics are n exactly simil>1 & !re=e ! load is unequally di/ribut$1 "s be+ ov]load$1 :ile o!rs d n take up _! prop] %>e ( ! "w4 ,,note4--,! action ( an equaliz+ b> 9 equaliz+ ! load on comp\nd dynamos run 9 p>allel may be expla9$ z foll[s3 ,! comp\nd w9d+ ( a dynamo raises ! pressure 9 proportion to ! curr5t fl[+ ?r\gh x1 & if1 9 a sy/em ( p>allel op]at$ comp\nd dynamos )\t ! equaliz+ connection1 ! curr5t giv5 by "o ma*9e 7 slightly great] ?an ! curr5ts f ! o!rs1 ! pressure ( t ma*9e w\ld increase4 ,) ?is increase 9 pressure above ! o!r ma*9es1 a /ill great] curr5t w\ld fl[1 & s raise ! pressure fur!r4 ,! effect is !re=e cumulative1 & 9 "t ! "o dynamo w\ld be c>ry+ too great a proportion ( ! :ole curr5t ( ! sy/em4 ,) ! equaliz+ connection1 :atev] ! curr5t fl[+ f ea* ma*9e1 ! curr5ts 9 ! v>i\s comp\nd w9d+s are all equal1 & s ! add$ pressure due to ! comp\nd w9d+ is practically ! same 9 ea* ma*9e4 ,any inequality 9 output f ! ma*9es is readily elim9at$ by adju/+ ! %unt curr5ts by means ( ! %unt rheo/ats4 ,:5 comp\nd w\nd dynamos are op]at$ 9 p>allel1 ! equaliz] b> insures uni=m di/ribution among ! s]ies coils ( ! ma*9es4 ,,note4--,to secure ! be/ results 9 p>allel op]ation1 dynamos %\ld be ( ! same design & con/ruction & %\ld possess z ne>ly z possible ! same *>act]i/ics2 t is1 ea* %\ld respond ) ! same read9ess1 & to ! same ext5t1 to any *ange 9 its field excitation4 ,any numb] ( su* ma*9es may be op]at$ 9 p>allel4 ,! usual practice is to connect ! equaliz] & ! s]ies field to ! positive t]m9al1 ?\gh if desir$1 !y may be connect$ to ! negative t]m9al2 bo? h[ev]1 mu/ be connect$ to ! same t]m9al4 ,! resi/ance ( ! equaliz] %\ld be z l[ z possible1 & x mu/ nev] be great] ?an ! resi/ance ( any ( ! leads f ! dynamos to ! bus b>4 ,sometimes a ?ird wire is run to ! swit*bo>d f ea* dynamo & !re connect$ to an equaliz] b>1 b ! usual practice is to run ! equaliz] directly betwe5 ! dynamos & to place ! equaliz] swit*es on p$e/als ne> ! ma*9es4 ,?is %ort5s ! connections & leads to bett] regulation4 ,! positive & equaliz] swit*es ( ea* ma*9e diff] 9 pressure only by ! slight drop 9 ! s]ies coil1 & 9 "s l>ge /ations ^! two swit*es are plac$ side by side on a p$e/al ne> ! ma*9e4 ,9 su* cases1 ! equaliz] & positive bus b>s are (t5 plac$ "u ! floor ne> ! ma*9es1 s t all leads may be z %ort z possible4 ,if all ! dynamos be ( equal capacity1 all ! leads to bus b>s %\ld be ( ! same l5g?1 & x is sometimes necess>y to loop "s ( !m4 ,if ! diff]5ce be small1 x may be comp5sat$ by means ( ! h& regulator2 if l>ge1 h[ev]1 o!r means mu/ be tak5 to cause ! ma*9es to take up _! due proportion ( ! load4 ,if ! s]ies coils ( ! sev]al dynamos be provid$ ) small adju/able resi/ances1 9 ! =m ( ,g]man silv] or copp] ribbon ins]t$ 9 s]ies ) ! coils1 ! di/ribution ( ! curr5t 9 ! latt] may be alt]$ by v>y+ ! resi/ance atta*$ to ! individual coils4 ,! effect ( ! s]ies coils ^u ! individual armatures 9 rais+ ! pressure may be adju/$1 & ! load ?us ev5ly divid$ among ! ma*9es4 ,%unt & ,comp\nd ,dynamos 9 ,p>allel4--,x is n practicable to run a comp\nd dynamo & a %unt dynamo 9 p>allel1 =1 unless ! field rheo/at ( ! %unt ma*9e be adju/$ cont9ually1 ! comp\nd dynamo w take m ?an its %>e ( ! load4 ,,*apt] ,,xxxi ,,dynamo ,,fails ,,to ,,excite ,?is tr\ble is ( frequ5t occurr5ce 9 bo? old & new ma*9es4 ,if a dynamo fail to excite1 ! op]ator %\ld fir/ see t ! bru%es are 9 ! prop] position & mak+ good contact1 & t ! ext]nal circuit is op5 if ! ma*9e be %unt w\nd1 & clos$ if s]ies w\nd4 ,9 />t+ a dynamo x %\ld be rememb]$ t %unt & comp\nd ma*9es require an appreciable "t to build up1 h5ce1 x is be/ n to be too ha/y 9 hunt+ = faults4 ,! pr9cipal causes :i* prev5t a dynamo build+ up are3 #a4 ,bru%es n prop]ly adju/$2 #b4 ,defective contacts2 #c4 ,incorrect adju/m5t ( regulators2 #d4 ,spe$ too l[2 #e4 ,insuffici5t residual magnetism2 #f4 ,op5 circuits2 #g4 ,%ort circuits2 a4 ,9 ext]nal circuits2 b4 ,9 dynamo4 #h4 ,wrong connections2 #i4 ,rev]s$ field magnetism4 ,bru%es n ,prop]ly ,adju/$4--,if ! bru%es be n 9 or ne> _! correct positions1 ! :ole ( ! voltage ( ! armature w n be utiliz$1 & w probably be insuffici5t to excite ! ma*9e4 ,if 9 d\bt z to ! correct positions1 ! bru%es %\ld be rotat$ by means ( ! rock] into v>i\s po9ts on ! commutator1 suffici5t "t be+ giv5 ! ma*9e to excite be=e mov+ !m into a new position4 ,defective ,contacts4--,if ! diff]5t po9ts ( contact ( ! connections ( ! ma*9e be n kept ?or\ghly clean & free f oil1 etc41 x is probable t en\gh resi/ance w be int]pos$ 9 ! pa? ( ! excit+ curr5t to prev5t ! ma*9e build+ or excit+4 ,ea* ( ! contacts %\ld !re=e be exam9$1 clean$1 & screw$ up tight4 ,ques4 ,:i* ( ! contacts %\ld receive special att5tion8 ,ans4 ,! contact faces ( ! bru%es & surface ( ! commutator4 ,^! are v frequ5tly cov]$ ) a slimy coat+ ( oil & dirt1 :i* is q suffici5t to prev5t ! ma*9e excit+4 ,incorrect ,adju/m5t ( ,regulators4--,:5 %unt & comp\nd ma*9es are provid$ ) field regulators1 x is possible t ! resi/ance 9 circuit may be too great to p]mit ! necess>y /r5g? ( excit+ curr5t pass+ ?r\gh ! field w9d+s4 ,accord+ly1 ! fault is correct$ by cutt+ out m or less ( ! resi/ance4 ,! field coils ( s]ies ma*9es are sometimes provid$ ) %ort circuit+ swit*es or resi/ances arrang$ to %unt ! curr5t across ! field coils4 ,if too mu* ( ! curr5t be %unt$ across1 ! swit* %\ld be op5$1 or if !re be a regulator1 x %\ld be s adju/$ t x w pass en\gh curr5t ?r\gh ! field w9d+s to excite ! ma*9e4 ,spe$ too ,l[4--,9 %unt & comp\nd dynamos !re is a c]ta9 critical spe$ bel[ :i* !y w n excite4 ,if ! normal spe$ ( ! ma*9e be kn[n1 x c be se5 :e!r ! failure to excite arises f ?is cause1 by measur+ ! spe$ ( ! armature ) a spe$ indicator4 ,9 all cases x is advisable1 if ! ma*9e d n excite 9 ! c\rse ( a few m9utes1 to slightly increase ! spe$4 ,z soon z ! voltage rises1 ! spe$ may be r$uc$ to its regul> rate4 ,illu/ration3 ,fig4 #fib4--,me?od ( te/+ = break by %ort circuit+ ! t]m9als ( ! ma*9e4 ,if ! ext]nal circuit te/ out app>5tly all "r1 & !re be no defective contacts 9 any "p ( ! ma*9e1 & all %ort circuit+ swit*es1 etc41 be cut out ( circuit1 ! ma*9e /ill refus+ to excite1 %ort circuit+ ! t]m9als ( ! ma*9e %\ld be tri$4 ,?is %\ld be done v cauti\sly1 especially 9 case ( a high t5sion ma*9e4 ,x is advisable to h1 if possible1 only a portion ( ! load 9 circuit1 & ! %ort circuit %\ld be effect$ z %[n 9 ! figure4 ,! %ort circuit may be made by mom5t>ily bridg+ across ! two t]m9als ( ! ma*9e ) a s+le piece ( wire4 ,z ?is1 h[ev]1 is liable to burn ! t]m9als1 a bett] plan is to fix a %ort piece ( scrap wire 9 "o t]m9al1 & !n ) ano!r piece ( insulat$ wire make mom5t>y contacts ) ! o!r t]m9al & ! %ort piece ( wire4 ,if ! ma*9e excite1 x w be at once evid5t by ! arc :i* occurs betwe5 ! two pieces ( wire4 ,z ! voltage ( a s]ies ma*9e :5 induc$ to build 9 ?is mann] g5]ally rises v rapidly1 great c>e %\ld be tak5 t ! contact is at fir/ only mom5t>y1 m]ely a rubb+ or scrap+ t\* ( ! wires4 ,! contact may be prolong$ if ! ma*9e d n excite at ! fir/ contact4 ,comp\nd w\nd ma*9es c (t5 be made to excite quickly by %ort circuit+ _! t]m9als 9 ?is mann]4 ,insuffici5t ,residual ,magnetism4--,?is fault is n ( frequ5t occurr5ce2 x takes place *iefly :5 ! dynamo is new1 & may be rem$i$ by pass+ ! curr5t f a few /orage cells1 or f ano!r dynamo1 = "s "t 9 ! prop] direction ?r\gh ! field coils4 ,if a heavy curr5t1 su* z is obta9able f a /orage batt]y1 be n available1 & ! ma*9e be %unt or comp\nd w\nd1 a few prim>y cells arrang$ z 9 fig4 #fic w g5]ally suffice4 ,illu/ration3 ,fig4 #fic4--,me?od ( ov]com+ insuffici5t residual magnetism4 ,! flexible lead ,l ( ! dynamo ,d is disconnect$ f ! positive t]m9al ( ! ma*9e1 & is connect$ to ! negative or z9c pole ( ! batt]y ,b1 ! o!r or positive c>bon pole be+ connect$ to ! t]m9al1 f :i* ! lead 0 remov$1 & %unt circuit ,s4 ,z ?us arrang$1 x w be se5 t ! batt]y ,b is 9 s]ies ) ! armature & %unt circuit1 & !re=e its voltage w be add$ to any small voltage g5]at$ 9 ! armature4 ,:5 ! ma*9e is />t$1 ! comb9$ voltages w probably be able to s5d suffici5t curr5t ?r\gh ! %unt to excite ! ma*9e4 ,z ! voltage rises & ! /r5g? ( ! curr5t 9 ! %unt w9d+s increases1 ! flexible lead may be aga9 ins]t$ into ! t]m9al f :i* x 0 remov$4 ,! batt]y w ?us be %ort circuit$1 & may be cut out ( circuit )\t any dang] ( break+ ! %unt circuit1 & ?us caus+ ! ma*9e to demagnetize4 ,op5 ,circuits4--,dynamos are affect$ by op5 circuits 9 diff]5t ways1 dep5d+ ^u ! type4 ,s]ies ma*9es require clos$ circuit to build up1 :ile an op5 circuit is necess>y ) ! %unt ma*9e4 ,an op5 circuit may be due to3 #a1 brok5 wire or faulty connection 9 ! ma*9e2 #b1 bru%es n 9 contact ) commutator2 #c1 safety fuse bl[n or remov$2 #d1 circuit break] op52 #e1 swit* op52 #f1 ext]nal circuit op54 ,if ! tr\ble be due m]ely to ! swit* or ext]nal circuit be+ op51 ! magnetism ( a %unt ma*9e may be at full /r5g?1 & ! ma*9e itself may be work+ p]fectly1 b if ! tr\ble be 9 ! ma*9e1 ! field magnetism w probably be v weak4 ,op5 circuits are mo/ likely to occur 93 #a4 ,! armature circuit2 #b4 ,! field circuit2 #c4 ,! ext]nal circuit4 ,:5 ! op5 circuit is due to ! bru%es n mak+ good contact1 simple exam9ation g5]ally reveals ! fact4 ,ques4 ,:at causes breaks 9 ! field circuit8 ,ans4 ,bad contacts at ! t]m9als1 brok5 connections1 or fracture ( ! coil w9d+s4 ,ques4 ,h[ is ! field circuit te/$ = breaks8 ,ans4 ,! flexible leads atta*$ to ! bru%es are remov$ f _! connections ) ! field circuit1 & ! latt] is !n te/$ = conductivity ) a galvanomet]4 ,ques4 ,:]e is a break likely to occur 9 a %unt ma*9e8 ,ans4 ,9 ! h& regulator ?r\gh a brok5 resi/ance coil or bad contact4 ,v frequ5tly ! fault occurs 9 ! connect+ wires lead+ f ! ma*9e to ! h& regulator fix$ ^u ! swit*bo>d1 or 9 ! %ort wires connect+ ! field coils to ! t]m9als or bru%es4 ,! insulation ( a brok5 wire w sometimes hold ! two ends toge!r s z to defy any b ! mo/ c>eful inspection or exam9ation2 !re=e1 9 ord] to avoid loss ( "t1 x is advisable to disconnect ! wires if possible1 & te/ ea* sep>ately = conductivity ) a batt]y & galvanomet] connect$1 z 9 fig4 #fid4 ,if ! fault be n locat$ 9 ! v>i\s connections1 ! magnet coils %\ld be te/$ ) ! batt]y & galvanomet] c\pl$ up z 9 fig4 #gjf1 c>e be+ fir/ tak5 to disconnect ! ends ( ea* ( ! coils4 ,a faulty coil w n %[ any deflection ( ! galvanomet]4 ,illu/ration3 ,fig4 #fid4--,me?od ( te/+ dynamo = %ort circuits4 ,9 ! figure1 "o pole ( ! batt]y ,b is plac$ 9 contact ) ! frame ( ! ma*9e at a po9t :i* has previ\sly be5 well scrap$ & clean$2 ! o!r pole is connect$ to "o ( ! galvanomet] t]m9als z %[n4 ,! o!r t]m9al ( ! galvanomet] is connect$ to ea* ( ! dynamo t]m9als ,t ,t "u te/ 9 turn4 ,if a deflection ( ! ne$le be produc$ :5 ! galvanomet] t]m9al is 9 contact ) ei!r1 ! t]m9als are 9 contact ) ! frame1 & !y %\ld !n be remov$1 & ! fault repair$ by additional insulation or by re9sulat+4 ,ques4 ,at :at po9t ( a %unt coil does a break usually occur8 ,ans4 ,at ! po9t :]e ! wire passes ?r\gh ! flanges ( ! spool or bobb94 ,ques4 ,h[ %\ld ! coil be repair$8 ,ans4 ,9 mo/ cases a little ( ! wood or metal ( :i* ! flange is made c be g\g$ or *ipp$ out1 & a new connect+ wire sold]$ on to ! brok5 end ( ! coil )\t mu* difficulty4 ,if x be necess>y to take ! magnets ap>t at any "t1 c>e %\ld be tak5 9 putt+ !m toge!r aga9 to wipe all faces p]fectly clean1 & screw up firmly into contact1 & to see t ! connections ( ! coils are made z !y 7 be=e be+ tak5 ap>t4 ,if ! faulty coil _c be repair$ quickly1 & ! ma*9e is urg5tly requir$1 ! coil may be cut out ( circuit entirely1 or %ort circuit$1 & ! rema9+ coils c\pl$ up s z to produce ! correct pol>ity 9 ! pole pieces4 ,illu/ration3 ,fig4 #fie4--,watson armature discs4 ,ea* lam9ation is made f l[ c>bon electrical /eel ( high magnetic p]meability4 ,ea* disc is anneal$ & aft]w>ds v>ni%$4 ,ques4 ,:at tr\ble is liable to be enc\nt]$ 9 op]at+ aft] cutt+ out a coil8 ,ans4 ,! rema9+ coils are liable to heat up to a great] ext5t ?an =m]ly1 ow+ to ! increas$ curr5t1 h5ce x is advisable to proce$ cauti\sly 9 />t+ ! dynamo1 s9ce ! temp]ature may exce$ a safe limit4 ,if ?is occur1 a resi/ance may be put 9 circuit ) ! field coils1 or ! spe$ ( ! dynamo r$uc$4 ,illu/ration3 ,fig4 #fif4--;,=t ,wayne p$e/al type commutator tru+ device4 ,:5 ?is device is us$1 ! armature is revolv$ 9 its own be>+s by means ( a h&le clamp$ to ! pulley4 ,! tool has a horizontal travel ( #ba ins41 7be+ #c ins4 wide inside ! fa/5+ bolt 9 ! base71 & a v]tical adju/m5t ( #ab ins41 adapt+ x to ma*9es ) commutators up to #cf ins4 9 diamet]4 ,illu/ration3 ,fig4 #fig4--;,=t ,wayne yoke type commutator tru+ device = ma*9es hav+ bru% me*anism m\nt$ on a yoke c>ri$ by ! field frame4 ,x consi/s ( a c>riage = ! tool hold] hav+ a screw fe$ & a bracket = atta*+ to ! bru% yoke4 ,! bracket replaces two bru% hold] brackets on ! bru% yoke1 & is made to fit ! yoke ( ! p>ticul> ma*9e on :i* x is to be us$4 ,ques4 ,:at k9d ( dynamo is affect$ by breaks 9 ! ext]nal circuit8 ,ans4 ,a s]ies dynamo4 ,ques4 ,"n ! k9d ( break t is difficult to locate4 ,ans4 ,a p>tial break4 ,%ort ,circuits4--,9 a s]ies or comp\nd dynamo a %ort circuit or heavy load w ov]load ! ma*9e & cause ! fuses to bl[4 ,a %unt ma*9e w n excite "u ^! circum/ances1 = ! reason t practically ! :ole ( ! curr5t g5]at$ 9 ! armature passes direct to ! ext]nal circuit1 & ! diff]5ce ( pot5tial betwe5 ! %unt t]m9als is practically nil4 ,ques4 ,:at %\ld be done if x be suspect$ t ! failure to excite arises f ?is cause8 ,ans4 ,! ma9 leads %\ld be tak5 out ( ! dynamo t]m9als1 !n1 if due to ?is cause1 ! ma*9e w excite4 ,ques4 ,:at p>ts ( a dynamo are specially liable to be %ort circuit$8 ,ans4 ,! t]m9als1 bru% hold]s1 commutator1 armature coils & field coils4 ,ques4 ,h[ are ! t]m9als liable to be %ort circuit$8 ,ans4 ,! t]m9als ( ! v>i\s circuits ( ! ma*9e are liable to be %ort circuit$1 ei!r ?r\gh metallic du/ bridg+ across ! insulation1 or ?r\gh ! t]m9als mak+ direct contact ) ! frame ( ! ma*9e4 ,! v>i\s t]m9als %\ld be exam9$1 & if ! fault _c be locat$ by inspection1 !y %\ld ea* be disconnect$ f _! circuits & te/$ ) a batt]y & galvanomet] arrang$ z 9 fig4 #fid4 ,ques4 ,:at precaution %\ld be tak5 ) ! bru% hold]s8 ,ans4 ,s9ce1 !y are liable to be %ort circuit$ ?r\gh ! rock] by metallic du/ lodg+ 9 ! insulat+ wa%]s1 !y %\ld be kept clean4 ,ques4 ,h[ are ! bru% hold]s te/$8 ,ans4 ,a galvanomet] & batt]y are connect$ 9 s]ies ) "o t]m9al ( ! galvanomet] connect$ to "o set ( bru%es2 ! unconnect$ t]m9al ( ! batt]y is !n connect$ ) ! o!r set ( bru%es4 ,a deflection ( ! ne$le w indicate a %ort circuit4 ,illu/ration3 ,fig4 #fih4--;,field coil te/+ ) telephone receiv]4 ,9 ! me?od "h %[n1 a telephone receiv] is connect$ 9 s]ies ) two symmetrically plac$ coils ,a & ,b4 ,v little s\nd w be he>d :5 ! flux ?r\gh ! two coils ,,ab is ! same2 b if a %ort-circuit$ coil is be+ te/$1 ! fluxes ?r\gh ! coils ,a1 ,b w n be equal & a noise c be he>d 9 ! receiv]4 ,ques4 ,:at is ! effect ( a %ort circuit 9 ! field coils or field circuit8 ,ans4 ,! ma*9e g5]ally refuses to excite4 ,ques4 ,h[ are ! field coils te/$ = %ort circuit8 ,ans4 ,by measur+ ! resi/ance ( ea* coil ) an ohmmet] or ,:eat/one bridge4 ,! faulty coils w %[ a mu* less resi/ance ?an ! p]fect coils4 ,! fault may also be discov]$ & locat$ by pass+ a /rong curr5t f a batt]y or ano!r dynamo ?r\gh ea* ( ! coils 9 turn1 & obs]v+ ! relative magnetic effects produc$ by ea* ^u a b> ( iron held 9 _! vic9ity4 ,! %ort circuit may be 9 ! t]m9als or connections1 & ^! %\ld fir/ be exam9$ & te/$4 ,"s s]ies dynamos are provid$ ) a resi/ance1 arrang$ 9 p>allel or %unt ) ! field coils1 to div]t a portion ( ! curr5t !refrom1 & ?us regulate ! output4 ,:5 mak+ a s]ies dynamo excite1 all resi/ances & controll+ devices %\ld be tempor>ily cut out ( circuit by op5+ ! %unt circuit4 ,s]ies ma*9es h frequ5tly a swit* :i* %ort circuits ! field coils4 ,c>e %\ld be tak5 t ?is is op51 or o!rwise ! ma*9e w n excite4 ,illu/ration3 ,fig4 #fii4--,watson armature complete4 ,! armature coils are =m w\nd1 heavily insulat$ & s m\nt$ on ! core z to insure rapid dissipation ( heat by v5tilation4 ,ea* coil is protect$ by an insulat+ %ea? & tape cov]+ be=e m\nt+4 ,! armature is bak$ aft] ! coils are m\nt$ to drive out all moi/ure1 !n1 :ile hot1 is treat$ ) insulat+ comp\nd & aga9 bak$ twelve h\rs4 ,wrong ,connections4--,:5 a ma*9e is fir/ erect$1 ! failure to build up may be due to incorrect connections4 ,! :ole ( ^! latt] %\ld !re=e be trac$ or foll[$ out1 & comp>$ ) ! diagrams ( dynamo connections giv5 9 figs4 #aij to #aih4 ,sometimes errors are made 9 connect+ ! field coils1 caus+ !m to act 9 opposition4 ,?is may occur :5 ! dynamo is a new "o or ! coils h be5 remov$ = repairs4 ,x may be caus$ ei!r ?r\gh ! coils hav+ be5 put on ! field cores ! wrong way1 or ?r\gh incorrect c\pl+ up4 ,"u ^! circum/ances1 ! dynamo1 if bipol>1 w fail to excite2 & if multipol>1 poles w be produc$ 9 ! yokes1 etc4 ,x may be rem$i$ by remov+ "o ( ! coils f ! core & putt+ x on ! rev]se way1 or by rev]s+ its connections4 ,! correctness ( connections ( all ! coils %\ld be v]ifi$4 ,9 comp\nd dynamos x sometimes happ5s t ! ma*9e w excite prop]ly1 b t ! s]ies coils t5d to rev]se ! pol>ity ( ! dynamo1 ?us r$uc+ ! voltage z ! load ^u ! ma*9e increases4 ,?is may be detect$ :5 ! ma*9e is load$ by %ort circuit+ ! s]ies coils1 n ! t]m9als4 ,if ! voltage rise 9 do+ ?is1 ! s]ies coils are act+ 9 opposition to ! %unt coils1 & ! connections ( ! s]ies coils mu/ be rev]s$4 ,rev]s$ ,field ,magnetism4--,?is is sometimes caus$ by ! ne>ness ( o!r dynamos1 b is g5]ally due to rev]s$ connections ( ! field coils4 ,"u su* conditions ! field coils t5d to produce a pol>ity oppos$ to ! magnetization to :i* !y owe _! curr5t1 & !re=e ! ma*9e w refuse to excite until ! field connections are rev]s$1 or a curr5t is s5t f ano!r dynamo or a batt]y ?r\gh ! field coils 9 a direction to produce ! correct pol>ity 9 ! pole pieces4 ,,*apt] ,,xxxii ,,armature ,,tr\bles ,a l>ge proportion ( ! mi%aps & breakd[ns :i* occur ) dynamos & motors arise f causes m /rictly )9 ! prov9ce ( ! man 9 *>ge ?an 9 t ( ! design]4 ,! armature1 be+ a complex & delicately built /ructure1 is subject 9 op]ation to v>i\s detrim5tal influ5ces giv+ rise to faults4 ,_m ( ! faults :i* occur are avoid$ by op]ators bett] in=m$ z to ! electric & magnetic conditions :i* obta9 9 ! runn+ ( ! ma*9e1 especially ! me*anical /resses on ! copp] inductors due to ! magnetic field & ! necessity ( pres]v+ prop] insulation4 ,! *ief mi%aps to :i* armatures are subject are z foll[s3 #a4 ,%ort circuits2 a4 ,9 individual coils2 b4 ,betwe5 adjac5t coils2 c4 ,?r\gh frame or core2 d4 ,betwe5 sections ( armature2 e4 ,p>tial %ort circuits4 #b4 ,gr\nds2 #c4 ,breaks 9 armature circuit4 ,%ort ,circuit 9 ,individual ,coils4--,?is is a common fault1 :i* makes its pres5ce kn[n by a viol5t heat+ ( ! armature1 fla%+ at ! commutator1 flick]+ ( ! light on light+ circuits1 & by a smell ( burn+ v>ni% or ov]heat$ insulation4 ,:5 ^! indications are pres5t1 ! ma*9e %\ld be /opp$ at once1 o!rwise ! armature is liable to be burnt out4 ,! fault is due ei!r to metallic du/ lodg+ 9 ! insulation betwe5 adjac5t b>s ( ! commutator1 or to "o or m convolutions ( ! coils com+ into contact ) ea* o!r1 ei!r ?r\gh a metallic fil+ becom+ emb$d$ 9 ! insulation or damage to ! insulation4 ,illu/ration3 ,fig4 #gjj4--,me?od ( locat+ %ort circuit$ armature coil4 ,disconnect ! ext]nal & field circuits f ! armature1 & pass a l>ge curr5t--say f #bj to #ajj amp]es--f a batt]y 7,b7 or ano!r dynamo ?r\gh ! :ole armature by means ( ! bru%es4 ,!n1 hav+ previ\sly well clean$ ! commutator1 measure ! diff]5ce ( pot5tial betwe5 adjac5t segm5ts all r\nd ! commutator 7,c71 by means ( a voltmet] or galvanomet] 7,g71 ! t]m9als ( :i* are connect$ to adjac5t segm5ts1 z %[n4 ,! %ort circuit$ coil or coils w be locat$ by ! diff]5ce ( pot5tial betwe5 ! correspond+ segm5ts be+ little or no?+4 ,x may be rem>k$1 h[ev]1 t ?is is n always a decisive te/4 ,9 "s cases ! %ort circuit may be int]mitt5t1 or may disappe> z soon z ! armature ceases to rotate4 ,9 su* cases1 ! %ort circuit is caus$ by ! wire com+ into contact ?r\gh ! action ( ! c5trifugal =ces develop$ by ! rotation ( ! armature4 ,ques4 ,h[ is ! faulty coil locat$8 ,ans4 ,:5 ! ma*9e is /opp$1 ! faulty coil1 if n burnt out1 c g5]ally be locat$ by ! bak$ appe>ance ( ! v>ni% or insulation1 & by its excessive temp]ature ov] ! re/ ( ! coils1 be+ detect$ also by ! bak$ appe>ance ( ! v>ni% or insulation4 ,ques4 ,:at %\ld be done if ! ma*9e d n build1 & x be suspect$ t ! fault is due to %ort circuit$ armature coils8 ,ans4 ,! field magnets %\ld be excit$ by ! curr5t f a /orage batt]y or ano!r dynamo1 &1 hav+ rais$ ! bru%es f contact ) ! commutator1 ! armature %\ld be run = a %ort "t4 ,9 /opp+1 ! faulty coil or coils may be locat$ by ! heat g5]at$ by ! %ort circuit4 ,:5 ! dynamo is />t$ = ! purpose ( localiz+ a %ort circuit1 precautions %\ld be tak51 & ! ma*9e only run = a few m9utes at a "t until ! faulty coil is detect$4 ,:5 ! faulty coil has be5 locat$1 ! insulation betwe5 ! segm5ts ( ! commutator to :i* its ends are connect$ %\ld be c>efully exam9$ = any?+ t may bridge across f segm5t to segm5t1 & scrap$ clean4 ,if ! commutator be app>5tly all "r1 ! fault probably lies 9 ! w9d+4 ,! insulation ( ! w9d+ %\ld be c>efully exam9$1 & any metallic fil+s or o!r p>ticles discov]$ !re9 c>efully remov$1 & a little %ellac v>ni% appli$ to ! faulty "p4 ,illu/ration3 ,fig4 #gja4--,te/ = break 9 armature lead4 ,clean ! bru%es & commutator1 & apply curr5t f a few cells ( batt]y hav+ a telephone receiv] 9 circuit z %[n 9 ! figure4 ,if ! ma*9e h m ?an two bru%es1 connect ! leads to two adjo9+ bru%es & raise ! o!rs4 ,n[ rotate ! armature sl[ly by h& & !re w be a di/9ct click 9 ! receiv] z ea* segm5t passes "u ! bru%es until "o bru% be>s on ! segm5t at fault1 :5 ! click+ w cease4 ,9 mak+ ?is te/1 ! bru%es mu/ n cov] m ?an a s+le segm5t4 ,ques4 ,if ! insulation on adjac5t conductors has be5 abrad$1 h[ %\ld x be repair$8 ,ans4 ,a small boxwood or o!r h>dwood w$ge1 coat$ ) %ellac v>ni% %\ld be driv5 9 tightly betwe5 ! wire2 ?is w g5]ally be suffici5t4 ,illu/ration3 ,fig4 #gjb4--;,b> to b> te/ = op5 circuit 9 coil or %ort circuit 9 "o coil or betwe5 segm5ts4 ,if1 9 te/+ z 9 fig4 #gja1 on rotat+ ! armature completely ar\nd1 ! receiv] indicate no break 9 ! leads1 connect ! batt]y leads directly to ! bru%es1 z %[n 9 ! above figure1 & t\* ! connections f ! receiv] to two adjac5t b>s1 work+ f b> to b>4 ,! click+ %\ld be sub/antially ! same betwe5 any two commutator b>s2 if ! click+ sudd5ly rise 9 tone betwe5 two b>s1 x indicates a high resi/ance 9 ! coil or a break 7op5 circuit74 ,ques4 ,if a faulty coil _c be quickly repair$ & ! dynamo be ne$$1 :at %\ld be done8 ,ans4 ,! coil may be cut out ( circuit1 & ! correspond+ commutator segm5ts connect$ toge!r ) a piece ( wire 7( a size proportionate to ! am\nt ( curr5t to be c>ri$71 sold]$ to ea*4 ,x w n be necess>y to cut out & remove ! entire coil4 ,if ! active portions only be sep>at$ s t !y d n =m a clos$ circuit1 x w answ] ! purpose4 ,if ! wires be cut ) a *isel at ! po9t :]e !y pass ov] ! ends ( ! core1 & ! ends sep>at$1 x w be q z effective z remov+ ! entire coil4 ,x is wise1 ( c\rse1 to rew9d ! coil at ! fir/ opportunity4 ,illu/ration3 ,fig4 #gjc4--;,alt]nate b> te/ = %ort circuit betwe5 sections4 ,:]e two adjac5t commutator b>s are 9 contact1 or a coil betwe5 two segm5ts becomes %ort circuit$1 ! b> to b> te/ describ$ 9 fig4 #gjb w detect ! fault by ! telephone receiv] rema9+ sil5t4 ,if a %ort circuit be f\nd1 ! leads f ! receiv] %\ld !n include or /raddle ?ree commutator b>s1 z "h %[n4 ,! normal click w !n be twice t betwe5 two segm5ts until ! faulty coils are rea*$1 :5 ! click+ w be less4 ,:5 ?is happ5s1 te/ ea* coil = tr\ble &1 if individually !y be all "r1 ! tr\ble is betwe5 ! two4 ,to te/ = a gr\nd place "o t]m9al ( ! receiv] on ! %aft or frame ( ! ma*9e1 & ! o!r on ! commutator4 ,if !re be a click x indicates a gr\nd4 ,move ! t]m9al ab\t ! commutator until ! lea/ click+ is he>d & at or ne> t po9t w be f\nd ! contact4 ,gr\nds 9 field coils c be locat$ 9 ! same mann]4 ,%ort ,circuits betwe5 ,adjac5t ,coils4--,9 r+ armatures ! pres5ce ( ?is fault does n necess>ily imply t ! ma*9e w n build2 9 drum armatures1 w\nd into a s+le lay] ( conductors1 x entirely prev5ts ?is occurr+4 ,ref]5ce to a w9d+ diagram w %[ t adjac5t coils are dur+ a c]ta9 p]iod ( ! revolution at ! full diff]5ce ( pressure g5]at$ by ! ma*9e4 ,h5ce1 if any two adjac5t coils be connect$ toge!r or %ort circuit$1 ! :ole ( ! armature w be practically clos$ on itself1 any curr5t g5]at$ fl[+ )9 ! armature only4 ,l>ge drum armatures w\nd ) compress$ & /r&$ b>s & connectors are p>ticul>ly susceptible to ?is fault1 a slight bl[ g5]ally =c+ "o or m ( ! /r&s into contact ) ! adjac5t b>s1 ?us %ort circuit+ ! armature1 & r5d]+ x practically useless s f> z ! g5]ation ( curr5t is conc]n$4 ,9 ?is class ( %ort circuit 9 drum armatures1 ! me?od ( locat+ ! faulty coils by excit+ ! field1 & runn+ ! armatures on op5 circuit1 does n apply1 = ! reason t ! :ole armature w be heat$ equally4 ,a me?od ( locat+ su* fault is illu/rat$ 9 fig4 #gjd4 ,?is applies to drum w\nd armatures4 ,faults ( ?is description c frequ5tly be discov]$ by a c>eful inspection ( ! w9d+s ( ! armature )\t rec\rse to te/+4 ,:5 locat$1 ! fault c usually be repair$ ) a h>dwood w$ge1 z expla9$ above1 or a piece ( mica or vulcaniz$ fibre cem5t$ 9 place ) %ellac v>ni%4 ,illu/ration3 ,fig4 #gjd4--,me?od ( locat+ %ort circuits betwe5 adjac5t armature coils4 ,fa/5 a monkey wr5* to ! rim ( ! pulley1 or a crank to ! %aft4 ,n[1 excite ! fields1 &1 to make ! effects m m>k$1 connect ! coils 9 p>allel4 ,:5 ?is has be5 done x w require consid]able =ce to rotate ! armature1 & !n x w move q sl[ly1 except at "o position4 ,:5 ?is position has be5 f\nd1 m>k ! armature at po9ts 9 ! c5t] ( ! pole pieces at po9ts ,a & ,b & at bo? ends ( ! armature4 ,! explanation is t bo? halves ( ! armature oppose "o ano!r at ?is position2 b :5 n at ^! po9ts a cont9u\s circuit is =m$1 & ! resultant magnetic effect is consid]able4 ,! cross or %ort circuit is ne>ly always f\nd on ! commutator end 9 ! la/ half ( ! w9d+1 :]e ! wires pass d[n ?r\gh ! fir/ half t]m9als4 ,?is applies to an unequal w9d+4 ,9 armatures :]e ! w9d+s are equal1 x is z liable to occur at "o po9t z at ano!r4 ,) ?is me?od a defect c be f\nd & rem$i$ 9 a few mom5ts1 = x has always be5 a simple matt] to repair x :5 discov]$4 ,^! results c be obs]v$ 9 a p]fect armature by connect+ ! opposite sections ( ! commutator4 ,%ort ,circuits betwe5 ,sections ?r\gh ,frame or ,core ( ,armature4--,detection ( ?is fault c be effect$ by ! me?ods describ$ above1 & by disconnect+ ! :ole ( ! armature coils f ! commutator & f ea* o!r1 & te/+ ea* sep>ately ) a batt]y & galvanomet] c\pl$ up z 9 fig4 #gje1 "o wire be+ connect$ to ! %aft & ! o!r to ! end ( ! coil "u te/4 ,z a rule1 !re is no way ( rem$y+ ?is fault o!r ?an unw9d+ ! defective coils1 re9sulat+ ! core1 & rew9d+ new coils4 ,illu/ration3 ,fig4 #gje4--,me?od ( locat+ %ort circuits betwe5 coils ?r\gh armature core4 ,! galvanomet]1 batt]y & coil to be te/$ are connect$ 9 s]ies z %[n1 & !n ! unconnect$ t]m9al ( ! galvanomet] is br\ght into contact ) ! %aft4 ,if !n "s portion ( ! insulation ( ! wire has be5 abrad$ or de/roy$1 ?us br++ ! b>e wire into contact ) ! metal core1 z at ,a 9 ! figure1 ! ne$le ( ! galvanomet] w be deflect$ s9ce a clos$ circuit is =m$ ?r\gh ! core & wire4 ,if ! insulation be p]fect1 ! ne$le w n be deflect$4 ,x w ?us be se5 t 9 ! conductivity te/ 7fig4 #gjj7 x is necess>y t ! ne$le %\ld be deflect$1 or turn$1 to prove t all is "r1 :ile 9 ! insulation te/ ! conv]se holds good2 if ! ne$le be deflect$1 x proves t ! insulation is brok5 d[n4 ,%ort ,circuits betwe5 ,sections ?r\gh ,b9d+ ,wires4--,?is fault is ! result ( a loose w9d+1 & is caus$ by ! insulation ^u :i* ! b9d+ wires are w\nd giv+ way1 ?us br++ coils at diff]5t pressures toge!r4 ,z a consequ5ce ( ! heavy curr5t :i* fl[s1 ! b9d+ wires are z a rule unsold]$ or burn$4 ,! location ( ! fault c !re=e be effect$ by simple inspection4 ,to rem$y1 x w be necess>y to unw9d & rew9d on new b9d+ wires1 on b&s ( mica or vulcaniz$ fibre1 sold]+ at int]vals to obviate fly+ asund]4 ,p>tial ,%ort ,circuits 9 ,armatures4--,?is is usually due to ! pres5ce ( moi/ure 9 ! w9d+s4 ,to rem$y ! fault1 ! armature %\ld be tak5 out & expos$ to a mod]ate heat1 or subject$ to a curr5t equal to t ord9>ily giv5 by ! dynamo4 ,"u ! action ( heat or ( ?is curr5t ! moi/ure w be gradually disp]s$4 ,:5 ?or\ghly dry1 & :ile /ill w>m1 a coat ( %ellac %\ld be appli$ to ! :ole ( ! w9d+s4 ,illu/ration3 ,fig4 #gjf4--,me?od ( te/+ = breaks4 ,! in/rum5ts are connect$ z %[n4 ,b is ! batt]y1 ,g ! galvanomet]1 & ,s ! coil ( wire be+ te/$4 ,"o t]m9al ( ! batt]y is connect$ to a t]m9al ( ! galvanomet]1 & ! o!r to "o ( ! ends ( ! coil "u te/4 ,! o!r t]m9al ( ! galvanomet] is connect$ to ! o!r end ( ! coil4 ,if ! connect+ wires be mak+ good electrical contact ) ! respective t]m9als1 & ! wire ( coil be+ te/$ be unbrok51 ! ne$le ( ! galvanomet] w be deflect$ z soon z a clos$ circuit is made by ! end ( ! coil com+ into contact ) ! galvanomet] t]m9al4 ,if ! wire ( ! coil be brok5 9 "s "p or ! ends ( ! connect+ wires d n make good electrical contact ) ! t]m9als1 ! ne$le w n be deflect$4 ,9 ord] to prev5t mi/akes1 x is advisable to te/ ! batt]y & galvanomet] connections & contacts by %ort circuit+ or br++ ! ends ( ! wire connect+ ! t]m9al ( ! galvanomet] & negative pole or ! batt]y toge!r be=e />t+ to te/ ! circuit or coil4 ,if ! ne$le be deflect$1 ! connections are all "r2 if n deflect$1 !re is a bad contact some:]e1 :i* mu/ be made good be=e ! te/ c proce$4 ,burn+ ( ,armature ,coils4--,! reason = ! burn+ ( an armature coil may be expla9$ z foll[s3 ,! coil1 segm5ts1 & ! %ort circuit betwe5 ! segm5ts =m a clos$ circuit ( l[ resi/ance s t x is only necess>y to h a l[ pressure set up 9 ! active portion ( ! coil to =ce a v l>ge curr5t ?r\gh ! coil & ! %ort circuit$ commutator b>s4 ,! heat+ effect ( ?is curr5t is suffici5t to burn out ! coil4 ,illu/ration3 ,fig4 #gjg4--,watson field coils4 ,automatic ma*9]y is employ$ to w9d ^! coils2 aft] w9d+1 !y are b\nd ) tape1 !n bak$ to expel all moi/ure1 & :ile hot1 are saturat$ ) an insulat+ comp\nd & aga9 bak$ = twelve h\rs to make !m practically oil & wat] pro(4 ,heavy flexible leads are br\ght out to avoid dang] ( break+ or o!r damage4 ,cutt+ ,out ,damag$ ,armature ,coils4--,to cut out a damag$ coil f an armature1 fir/1 disconnect ! coil f ! commutator1 & aft] cutt+ (f ! leads1 insulate ! expos$ p>ts ) tape4 ,!n connect ! commutator b>s 7:i* 7 connect$ ) ! leads7 ) a wire ( ! same size z ! wire w9d+4 ,to remove ! coil entirely1 cut ! b& wire or remove ! w$ges1 & lift up a suffici5t numb] ( leads & coils to p]mit ( ! removal ( ! damag$ coil4 ,gr\nds 9 ,armatures4--,^! faults occur :5 ! armature coils become connect$ to ! frame or core ( ! armature4 ,:5 ?is gr\nd+ is conf9$ to a s+le coil1 x is n 9 itself liable to d damage4 ,a simple me?od ( locat+ a gr\nd$ coil is illu/rat$ 9 fig4 #gjh4 ,illu/ration3 ,fig4 #gjh4--,me?od ( locat+ gr\nd$ armature coil4 ,b is a batt]y or dynamo circuit giv+ a curr5t ( a few amp]es ?r\gh ! armature by its own bru%es 7#a & #b74 ,at ,g is plac$ a r\ghly made galvanomet]1 to c>ry "s #be amp]es or s1 "o t]m9al be+ 9 connection ) ! %aft ( ! armature1 & ! o!r atta*$ to a movable bru% #c4 ,s9ce ! function ( ! p>ticul> galvanomet] is simply to %[ a deflection :5 a curr5t is pass+1 & to m>k z]o :5 !re is none1 a coil ( ?ick wire ) a pocket compass 9 ! c5t] w d all t is requir$1 b c>e mu/ be tak5 to remove x suffici5tly f> away f ! di/urb+ effects ( ! armature magnetism4 ,! mann] ( te/+ is z foll[s3 ,assume a /eady curr5t to be fl[+ f batt]y ,b ?r\gh ! armature2 t\* ! commutator ) bru% #c1 & a curr5t w fl[ ?r\gh ,g4 ,sl[ly rotate ! armature or ! bru% #c until ! galvanomet] ,g %[s no deflection4 ,! coil 9 contact ) #c w be f\nd to be gr\nd$4 ,a h& regulator or rheo/at ,r may be ins]t$ 9 s]ies ) ! batt]y or dynamo circuit to regulate ! /r5g? ( ! curr5t pass+4 ,ques4 ,:at is ! advantage ( ?is te/8 ,ans4 ,! damag$ coil c be locat$ )\t unsold]+ ! coils f ! commutator1 :i* is sometimes a difficult op]ation )\t prop] tools2 fur!r1 ! fault c frequ5tly be repair$ )\t disconnect+ any ( ! wires if its exact position be det]m9$4 ,magneto ,te/ = ,gr\nd$ ,armatures4--,a magneto te/ = gr\nd$ armatures is n to be recomm5d$1 z armatures (t5 possess suffici5t /atic capacity to cause a magneto to r+ ev5 ?\gh !re be no leak4 ,?is is due to ! alt]nat+ curr5t giv5 by ! magneto = :5 ! circuit has capacity x acts z a cond5s] & at ea* revolution ( ! armature ( ! magneto a ru% ( curr5t goes out & returns1 *>g+ ! surfaces ( ! conductor alt]nately 9 opposite directions1 & r++ ! bell dur+ ! process4 ,illu/ration3 ,fig4 #gji4--,me?od ( b9d+ armature w9d+4 ,complete appliances = h&l+ armatures 9 mak+ repairs are usually n available ) mo/ /reet railway companies1 s9ce !y are s seldom requir$4 ,:5 ne$$1 !re=e1 "s tempor>y contrivance mu/ be resort$ to = help 9 ! dilemma4 ,%\ld an armature burn out1 "s local conc]n t makes coils & rew9ds armatures may be available to d ! "w2 aga91 x w be necess>y to s5d to ! manufactur]s = a man1 z soon z coils c be made ready = ! "w4 ,9 no case %\ld any b an exp]i5c$ man be giv5 *>ge ( ?is "w4 ,b if !re be any d\bt z to :e!r ! armature is really burnt out1 let a compet5t man be ! judge4 ,:5 a l>ge armature ne$s repair+1 a pair ( *a9 tongs c be us$ on "s "p ( ! %aft :5 putt+ 9 ! coils1 & a block & tackle1 z %[n1 c be us$1 :5 putt+ on ! b& wires4 ,d n f9i% "o b& & !n cut (f ! wire1 b run x ov] = ! next1 etc4 ,!n sold] & trim (f ! wires4 ,breaks 9 ,armature ,circuit4--,a p>tial or complete break 9 ! armature circuit is always accompani$ by heavy sp>k+ at ! commutator1 b n1 z a rule1 by an excessive heat+ ( ! armature or slipp+ ( ! belt1 & ?is enables ! fault to be di/+ui%$ f a %ort circuit4 ,! faulty "p c always be readily locat$ by ! flat :i* x produces ^u ! surface ( ! commutator4 ,! armature circuit be+ op5 at ! faulty "p1 heavy sp>k+ results at e half revolution z ! bru%es pass ov] x1 & z a consequ5ce ! correspond+ segm5ts become pitt$ or flatt5$ ) respect to ! o!rs2 !y may easily be discov]$ on exam9ation4 ,breaks 9 ! armature circuit may occur 9 ei!r ! commutator or 9 ! coils ( ! armature4 ,to asc]ta9 :e!r x be 9 ! latt]1 c>efully exam9e ! w9d+ ( ! faulty coil4 ,! defect may be s\ght = m p>ticul>ly at ! commutator end ( ! armature1 z breaks 9 ! wire are mo/ frequ5t :]e ! connections are made ) ! commutator segm5ts4 ,if no break c be discov]$1 try pass+ a heavy curr5t ?r\gh ! faulty coil by means ( ! bru%es4 ,if a p>tial break exi/ ) suffici5t contact to pass a curr5t1 ! coil w be heat$ at t po9t & may be discov]$ by runn+ ! f+]s ov] ! coil4 ,:5 locat$1 ! fault may be repair$ by rew9d+ ! coil1 or c>efully clean+ ! brok5 ends & jo9t+4 ,! fault may also be tempor>ily repair$ by sold]+ ! adjac5t commutator segm5ts toge!r )\t disconnect+ ! coil4 ,,*apt] ,,xxxiii ,,c>e ,,( ,,! ,,commutator ,,& ,,bru%es ,= satisfactory op]ation1 ! bru%es & commutator mu/ be kept 9 good condition4 ,to ?is end ! ma9 ?+ to be gu>d$ aga9/ is ! production ( sp>ks at ! bru%es4 ,if c>e be tak5 9 ! fir/ in/ance to adju/ ! bru%es to _! sett+ m>ks1 & to regulate _! pressure ^u ! commutator1 & aft]w>ds to att5d to ! lead z ! load v>ies1 s t little or no sp>k+ occurs1 & also to keep ! bru%es & commutator free f dirt1 grit1 excessive oil1 etc41 ! surface ( ! commutator w assume a d>k burni%$ appe>ance & we> w practically cease4 ,"u ^! circum/ances ! commutator w run cool1 & w give v little tr\ble4 ,9 ord] to ma9ta9 ^! conditions x w only be necess>y to see t ! bru%es are kept 9 prop] condition & f$ =w>d to _! sett+ m>ks1 z !y we> away1 & t ! commutator is occasionally poli%$4 ,if ! pressure ( ! bru%es ^u ! commutator be too great1 or _! adju/m5t faulty1 or ! commutator be all[$ to get into a dirty condition1 sp>k+ w result1 &1 if n at once att5d$ to & rem$i$1 ! bru%es w quickly we> away1 & ! surface ( ! commutator w be de/roy$4 ,z ?is action takes place1 9 ! e>li] /ages1 ! surface ( ! commutator w become r\gh5$ or scor$1 result+ 9 jump+ ( ! bru%es1 & increas$ sp>k+2 9 ! lat] /ages1 ! commutator w become untrue & worn into ruts1 moreov]1 ow+ to ! viol5t sp>k+ :i* takes place ?r\gh ?is circum/ance1 ! ma*9e w quickly be r5d]$ useless,d4 ,d ,,note4--,9 op]at+ dynamos hav+ metal bru%es1 x is ( importance to keep ! commutator smoo? & glossy4 ,to accompli% ?is1 x is necess>y to keep ! commutator & bru%es clean & free f grit1 & to occasionally lubricate ! commutator ) "s light oil1 su* z ord9>y ma*9e oil4 ,?is %\ld be done daily if ! ma*9e be 9 con/ant use4 ,keep ! bru%es re/+ ^u ! commutator ) j en\gh pressure to insure a good firm contact4 ,?is w be f\nd to be mu* less ?an ! spr+s are capable ( ex]t+4 ,a good me?od to foll[ 9 clean+ ! ma*9e is z foll[s3 ,loos5 ! bru% hold] ?umb screws & tilt ! bru%es (f ! commutator 7or1 if box bru% hold]s be us$1 take !m out ( _! hold]s74 ,!n run ! ma*9e & hold a clean clo? aga9/ ! commutator4 ,aft] ! commutator is clean1 hold aga9/ x a clo? or piece ( wa/e moi/5$ ) ma*9e oil & reset ! bru%es4 ,if = any reason ! bru%es beg9 to cut or score ! commutator1 x may be readily detect$ by hold+ ! f+] aga9/ ! commutator2 ! ridge may be easily felt by ! f+]4 ,?is %\ld be att5d$ to at once 9 ! foll[+ mann]3 ,tilt back ! bru%es 7or if box bru%es are us$ take !m out ( _! hold]s71 & hold lightly aga9/ ! commutator a piece ( ,no4 #jj s&pap] well moi/5$ ) oil1 pass+ x back & =? until ! surface is p]fectly smoo?4 ,!n wipe (f ! commutator ) a clean piece ( clo? or wa/e & lubricate ) ano!r clean piece moi/5$ ) oil & reset ! bru%es4 ,ques4 ,h[ is ! commutator easily te/$ z to ! condition ( its surface8 ,ans4 ,x is readily te/$ by re/+ ! back ( ! f+] nail ^u x :ile 9 motion2 ! nail be+ v s5sitive to any irregul>ities1 indicates at once any defect4 ,ques4 ,:at causes grooves or ridges to be cut 9 ! commutator8 ,ans4 ,!y result f us+ bru%es ) h>d burnt ends :i* are n pliable2 also by too great a pressure ( ! bru% ^u ! commutator surface4 ,sp>k+ at ! bru%es is exp5sive & detrim5tal1 *iefly because x results 9 burn+ ! bru%es & also ! commutator1 necessitat+ _! frequ5t r5ewal4 ,e sp>k consumes a p>ticle ( copp]1 torn f ! commutator or bru%4 ,! long] ! sp>k+ cont9ues1 ! great] ! evil becomes1 & ! rem$y mu/ be appli$ )\t delay4 ,ques4 ,:at k9d ( oil %\ld be us$ on ! commutator8 ,ans4 ,m9]al oil4 ,ques4 ,:at att5tion %\ld be giv5 to ! bru%es8 ,ans4 ,at c]ta9 int]vals1 accord+ to ! c>e tak5 to r$uce sp>k+ & ! l5g? ( "t ! ma*9e runs1 ! bru%es w fray out or we> unev5ly1 & w !re=e ne$ trimm+4 ,!y %\ld !n be remov$ f ! bru% hold]s & _! contact ends or faces exam9$4 ,if n truly squ>e1 !y %\ld be fil$ or clipp$ ) a pair ( %e>s1 ! c\rse ( treatm5t diff]+ ) ! type ( bru%4 ,if ! ma*9e be fitt$ ) metal /rip bru%es1 fray$ ends %\ld be clipp$ squ>e ) a pair ( %e>s1 ! ends ?or\ghly clean$ f any dirt or c>boniz$ oil1 & replac$ 9 _! hold]s4 ,gauze & wire bru%es require a little m att5tion4 ,:5 _! position on ! commutator has be5 well adju/$ & look$ aft]1 s t little or no sp>k+ has tak5 place1 x is g5]ally only necess>y to wipe !m1 clean ! bru%es & clip (f ! fr+$ edges & corn]s ) ! %e>s1 or a pair ( /rong scissors4 ,if1 h[ev]1 ! ma*9e has be5 sp>k+1 ! faces w be worn or burnt away1 & probably fus$4 ,if su* be ! case1 !y w ne$ to be put 9 ! fil+ clamp1 & fil$ true4 ,a conv5i5t me?od ( trimm+ c>bon bru%es1 or ( b$d+ a complete new set ( metal bru%es1 is to b9d a piece ( s&pap]1 face outw>ds1 ar\nd ! commutator aft] ! curr5t has be5 %ut (f1 & !n m\nt ! c>bon or metal bru%es 9 ! hold]s1 adju/+ ! t5sion ( ! spr+s s t ! bru%es be> ) a mod]ately /rong pressure ^u ! s&pap]4 ,!n let ! ma*9e run sl[ly until ! ends ( ! bru%es are gr\nd to ! prop] =m4 ,c>e %\ld be tak51 h[ev]1 t ! metal du/ giv5 (f does n get into ! commutator connections or armature w9d+s1 or %ort circuit+ w result4 ,if ! contact faces ( ! bru%es are v dirty & cov]$ ) a coat+ ( c>boniz$ oil1 etc41 x w be necess>y to clean !m ) b5zol9e or soda solution be=e replac+4 ,illu/ration3 ,fig4 #gaj4--;,bissell bru% ge>4 ,! bru%es are held 9 ! bru%hold]s radially & "w equally well ) armature runn+ 9 ei!r direction4 ,bru%es c be r5ew$ & adju/m5t made :ile ma*9e is 9 op]ation4 ,ques4 ,describe a fil+ clamp4 ,ans4 ,z usually con/ruct$1 x consi/s ( two pieces ( metal1 bo? %ap$ at "o end to ! correct angle1 to :i* ! bru%es mu/ be fil$4 ,"o ( ! pieces ( metal 7! back "p7 has a groove suffici5tly l>ge to accommodate ! bru%1 :i* is clamp$ 9 position by ! o!r piece ( metal & a p9*+ screw4 ,if ! clamp be n suppli$ ) ! ma*9e a conv5i5t sub/itute c be made out ( two pieces ( wood ab\t ! same wid? z ! bru%4 ,"o end ( ea* piece is sawn to ! correct angle1 & ! bru% plac$ betwe5 ! two4 ,9 fil+1 ! bru% is fix$ 9 ! clamp1 ) ! toe or tip project+ slightly ov] ! edge ( ! clamp1 & ! latt] be+ fix$ 9 a vise1 ! bru% is fil$ by s+le /rokes ( a smoo? file made outw>ds1 ! file be+ rais$ f contact ) ! bru% :5 mak+ ! back /roke4 ,illu/ration3 ,fig4 #gaa4--;,jig = fil+ bru%es to ! correct bevel2 us$ ) copp] bru%es to fit !m to ! commutator4 ,sp>k+4--,9 all well design$ ma*9es !re are c]ta9 positions ^u ! commutator = ! bru%es at :i* !re w be no sp>k+ s long z ! commutator is kept clean & 9 good condition4 ,9 o!r dynamos1 badly design$ or con/ruct$1 sp>k+ occurs at all positions1 no matt] :]e ! bru%es are plac$1 & 9 su* dynamos x is !re=e impossible to prev5t ?is no matt] h[ well !y are adju/$4 ,illu/ration3 ,fig4 #gab4--;,commutator clamp2 a useful device = hold+ ! segm5ts firmly 9 position 9 tak+ out ! end r+s ( ! commutator to repair = int]nal gr\nds4 ,x is made ( #b #a_/h in* %eet /eel1 ) a #a_/b in* screw4 ,! illu/ration cle>ly %[s ! adju/able fa/5+4 ,! not*es fit ar\nd rivets on "o side ( ea* fa/5+1 :i* c be mov$ by remov+ ! two cott]s4 ,! clamp is made loose or taut by screw+ ! bolt 9 ! nut4 ,ques4 ,:at two k9ds ( sp>k+ may be g5]ally di/+ui%$8 ,ans4 ,"o k9d ( sp>k+ is t due to bad adju/m5t ( ! bru%es1 & a second k9d1 t due to bad condition ( ! commutator4 ,sp>ks due to bad adju/m5t ( ! bru%es are g5]ally ( a blui% color1 small :5 ne> ! neutral plane1 & increas+ 9 viol5ce & brilliancy z ! bru%es rec$e f ! correct positions ^u ! commutator4 ,:5 sp>ks are produc$ by dirty or neglect$ /ate ( ! commutator1 !y are di/+ui%$ by a r$di% color & a splutt]+ or hiss+4 ,:5 due to ?is la/ m5tion$ cause1 x is impossible to suppress ! sp>k+ until ! commutator & bru%es h be5 clean$4 ,9 ! =m] case1 ! sp>ks w disappe> z soon z ! bru%es h be5 rotat$ into ! neutral po9ts4 ,ano!r class ( sp>ks appe> :5 !re is "s m or less develop$ fault1 su* z a %ort circuit1 or break 9 ! armature or commutator4 ,^! are simil> 9 "* to ^? produc$ by bad adju/m5t ( ! bru%es1 b are di/+ui%$ f ! latt] by _! n decreas+ 9 viol5ce :5 ! bru%es are rotat$ t[>ds ! neutral plane4 ,hav+ di/+ui%$ ! classes ( sp>ks :i* appe> at ! commutator ( a dynamo1 x rema9s to enum]ate ! causes :i* produce !m4 ,^! are3 #a4 ,bad adju/m5t ( bru%es2 #b4 ,bad condition ( bru%es2 #c4 ,bad condition ( commutator2 #d4 ,ov]load ( dynamo2 #e4 ,loose connections1 t]m9als1 etc42 #f4 ,breaks 9 armature circuit2 #g4 ,%ort circuits 9 armature circuit2 #h4 ,%ort circuits or breaks 9 field magnet circuit4 ,bad ,adju/m5t ( ,bru%es4--,:5 sp>k+ is produc$ by bad adju/m5t ( ! bru%es1 x may be detect$ by rotat+ or %ift+ ! rock]1 by ! indication t ! sp>k+ w v>y ) ea* movem5t4 ,to obta9 good adju/m5t ( ! bru%es1 x w be necess>y to rock !m g5tly backw>ds & =w>ds1 until a position is f\nd 9 :i* ! sp>k+ disappe>s4 ,ques4 ,if1 9 rock+ ! bru%es1 a position _c be f\nd at :i* ! sp>k+ disappe>s1 :at is ! probable cause ( ! tr\ble8 ,ans4 ,! bru%es may n be set ) ! prop] pit*1 t is !y may n be sep>at$ a correct di/ance1 or ! neutral plane may n be situat$ 9 ! true !oretical position ^u ! commutator ?r\gh "s defect 9 ! w9d+1 etc4 ,9 ?is la/ nam$ case1 ! bru%es may be /rictly adju/$ to _! !oretically correct positions be=e />t+ ! ma*9e2 !n1 :5 ! ma*9e is />t$ & ! load put on1 viol5t sp>k+ occurs1 :i* _c be suppress$ by %ift+ ! rock]4 ,if1 h[ev]1 "o set ( bru%es only be obs]v$1 x w g5]ally be f\nd t1 at a c]ta9 position1 ! sp>k+ at ! set ( bru%es "u obs]vation ceases or is greatly r$uc$1 :ile sp>k+ /ill occurs at ! o!r set4 ,:5 ?is position is f\nd1 ! rock] %\ld be fix$ by ! clamp+ screw1 & ! bru%es ( ! o!r set at :i* sp>k+ is /ill occurr+ adju/$ by draw+ !m back or pu%+ !m =w>d 9 _! hold]s until a position is f\nd at :i* ! sp>k+ ceases4 ,correct position ( ! bru%es & ! suppression ( sp>k+ is a matt] ( importance1 & any "t sp5t 9 c>efully adju/+ ! bru%es w be amply repaid by ! decreas$ att5tion & we> ( ! bru%es & commutator4 ,illu/ration3 ,figs4 #gac to #gae4--;,bru%es mak+ bad contact4 ,a bru% mak+ a bad contact1 z only at ! %ad$ portion ( figs4 #gac & #gad1 w n all[ ! %ort circuit$ coil en\gh "t to rev]se1 caus+ sp>k+ & heat+4 ,! latt] w also result f bad contact on acc\nt ( ! surface be+ too small = ! curr5t to be c>ri$ (f4 ,?is =m ( bad contact is worse ?an t %[n 9 fig4 #gae1 :]e ! area ( contact surface only is less5$4 ,if ! bru%es d n make good contact1 !y %\ld be gr\nd d[n4 ,bad ,condition ( ,bru%es4--,if ! contact faces ( ! bru%es be fus$ or cov]$ ) c>boniz$ oil1 dirt1 etc41 !re w be bad contact :i* is accompani$ by heat+ & sp>k+4 ,simple exam9ation w g5]ally reveal :e!r ?is be ! case4 ,! rem$y is to remove ! bru%es1 "o at a "t if ! ma*9e be runn+1 clean1 file if necess>y1 trim1 & readju/4 ,if ! bru%es be exce$+ly dirty1 or saturat$ ) oil1 x w be necess>y to clean !m ) turp5t9e1 b5zol9e1 or soda solution1 be=e replac+4 ,bad ,condition ( ,commutator4--,if ! surface ( ! commutator be r\gh1 worn into grooves1 or ecc5tric1 or if !re be "o or m segm5ts loose or set irregul>ly1 ! bru%es w be ?r[n into vibration1 & sp>k+ w result4 ,a simple exam9ation ( ! commutator w readily detect ^! defects4 ,a r\gh & unev5 commutator is due to bad adju/m5t ( bru%es1 bad con/ruction ( commutator1 & to neglect g5]ally4 ,if all[$ to cont9ue1 x results 9 heavy sp>k+ at ! bru%es1 & ! ev5tful de/ruction ( ! commutator4 ,! fault may be rem$i$ by fil+ or re-turn+ ! commutator4 ,illu/ration3 ,fig4 #gaf4--,r\gh & groov$ commutator due to improp] bru% adju/m5t & failure to keep bru%es 9 prop] condition4 ,ques4 ,h[ is an untrue commutator detect$8 ,ans4 ,if ! commutator be untrue1 ! fact w be indicat$ :5 ! ma*9e is sl[$ d[n by a visible ecc5tricity1 or by hold+ ! h&1 or a /ick 9 ! case ( a high t5sion ma*9e1 aga9/ ! surface :ile revolv+1 :5 any irregul>ity or ecc5tricity w be app>5t by ! vibration or movem5t ( ! /ick4 ,! only rem$y = an untrue commutator is to re-turn x 9 ! la!4 ,ques4 ,:at %\ld be done 9 case ( high segm5ts8 ,ans4 ,!y %\ld be g5tly tapp$ d[n ) a mallet1 & if possible ! clamp+ cones at ! commutator end %\ld be tight5$4 ,if x be impossible to hamm] ! segm5ts d[n1 !y %\ld be fil$ d[n to ! same diamet] z ! re/ ( ! commutator1 or ! commutator re-turn$4 ,= l[ segm5ts1 ! only rem$y is to pull out ! segm5ts1 or turn commutator d[n to _! level4 ,ques4 ,expla9 ! t]m flats on ! commutator4 ,ans4 ,?is is ! "n giv5 to a peculi> fault :i* develops on "o or m segm5ts ( ! commutator4 ,x is n conf9$ to dynamos ( bad design or con/ruction1 b frequ5tly appe>s on ^? ( ! highe/ class1 & may be recogniz$ z a pitt+ or flatt5+ ( "o or m segm5ts4 ,ques4 ,:at is ! effect ( flats on ! commutator8 ,ans4 ,sp>k+ at ! bru%es4 ,ques4 ,:at are ! causes :i* produce flats8 ,ans4 ,p]iodical jump+ ( ! bru%es due to a bad /ate ( ! commutator1 bad jo9t 9 ! driv+ belt1 a flaw1 or a diff]5ce 9 ! composition ( ! metal ( ! p>ticul> b> ^u :i* x appe>s4 ,b m frequ5tly flats may be trac$ to a m or less develop$ fault1 su* z a break1 ei!r p>tial or complete1 9 ! armature coil4 ,! break may occur ei!r 9 ! coil itself1 or at ! po9t :]e its ends make connection ) ! lug ( ! commutator1 or at ! po9t :]e ! lug is sold]$ to ! segm5t4 ,ques4 ,:at %\ld be done 9 case ( flats8 ,ans4 ,! bru%es %\ld be exam9$ to see if any p]iodical vibration take place4 ,if su* be ! case1 ! cause %\ld be remov$1 ! flat c>efully fil$ or turn$ out1 & ! bru%es readju/$4 ,if x be due to a diff]5ce 9 ! composition ( ! metal ( :i* ! segm5t is made1 ! flat w exi/ z long z ! p>ticul> segm5t is 9 use1 & w ne$ p]iodic att5tion4 ,) h>d drawn copp] or phosphor bronze segm5ts1 ?is fault is r>ely due to ?is la/ m5tion$ cause4 ,x is m frequ5tly due to bad sold]+1 ( ! conductors to ! lugs1 or ( ! lugs to ! segm5ts4 ,9 all cases ( flats1 if ! disconnection 9 ! armature circuit be n complete1 & _c be readily locat$1 ! effect ( re-sold]+ or sweat+ ! ends ( ! coils into ! lugs %\ld be tri$4 ,flats may also frequ5tly be cur$ by drill+ & tapp+ a small hole 9 ! junction betwe5 ! lug & ! segm5t1 & ins]t+ a small screw1 or bit ( screw$ copp] or brass wire1 aft]w>ds fil+ d[n level ) ! surface ( ! commutator4 ,illu/ration3 ,figs4 #gag & #gah4--,me?od ( repair+ brok5 jo9t betwe5 commutator segm5t & lug4 ,to repair su* a break pu% asbe/os 9 betwe5 adjac5t b>s1 s t heat f ! tor* w n affect !m4 ,asbe/os %\ld also be work$ 9 at ! back if possible1 = ! purpose ( keep+ sold] f places :]e x w\ld cause tr\ble4 ,!n unsold] ! armature leads f ! lug & remove ! latt]4 ,next1 ) specially made cape *isels1 cut 9 a slot 9 ! commutator b> = a new lug4 ,c>e & skill are requir$ n to de/roy ! mica insulation betwe5 ! segm5ts4 ,! slot %\ld be cut "o-qu>t] to ?ree-eigh?s in* deep4 ,! connector is !n sold]$ 9 place4 ,) c>e a satisfactory connection c be made 9 ?is way1 :i* w la/ well4 ,if x d n la/1 ! tr\ble 9 almo/ e case is due to poor sold]+4 ,%ort circuits sometimes occur aft] ?is op]ation1 because ( sold] fall+ 9 at ! back & lodg+ on l[] connections4 ,9 l>ge ma*9es1 ! excessive curr5t fl[+ is q likely to melt ?is sold]1 & ! ma*9e may buck1 ?r[+ out ! melt$ sold]1 aft] :i* x may be all "r aga94 ,:ile ! b> connector is out1 h[ev]1 asbe/os %\ld be pack$ 9 back ( x to prev5t ?is occurr5ce1 :i* may be a s]i\s affair4 ,all surplus sold] & ! asbe/os pack+ %\ld be remov$ aft] ! connection is f9i%$1 & ! connections clean$ ) compress$ air4 ,! armature %\ld be turn$ ov] sl[ly1 air be+ appli$ all ! :ile4 ,segm5ts ,loose or ,knock$ ,94--,:5 ! segm5ts are loose1 x is an indication t ! clamp+ r+ or cone has work$ loose4 ,?is %\ld !re=e be tight5$ up1 & ! commutator re-turn$ if necess>y4 ,ques4 ,h[ %\ld l[ commutator segm5ts be treat$8 ,ans4 ,! commutator surface may be turn$ d[n to ! level ( ! l[ segm5t1 or ! latt] may be pull$ out aga9 to its =m] level1 ?is latt] be+ ! pref]able me?od1 if x c possibly be effect$4 ,ques4 ,h[ is a commutator segm5t pull$ out to its correct position8 ,ans4 ,a h& vise is firmly clamp$ to ! lug1 or a loop ( copp] wire is pass$ r\nd ! conductor :]e x jo9s ! commutator4 ,a b> ( iron1 to act z a lev]1 is support$ on a fulcrum ov] ! commutator1 & "o end ( ! b> is pass$ ?r\gh ! loop or vise4 ,pressure is appli$ to ! o!r end :i* w g5]ally bury ! segm5t up to its prop] position4 ,h[ to ,re-turn a ,commutator4--,9 re-turn+ ! commutator1 ! armature %\ld fir/ be c>efully tak5 out ( ! armature *amb]1 avoid+ knocks or bl[s ( any k9d4 ,! :ole ( ! w9d+ %\ld !n be wrapp$ 9 calico or canvas be=e ! armature is put into ! la!1 to prev5t any p>ticles ( metal becom+ atta*$ to ! surface ( ! armature at ! "t ! commutator is be+ turn$4 ,! armature %\ld on no acc\nt be roll$ ^u ! floor1 or subject$ to bl[s or knocks :ile be+ put into ! la!4 ,9 re-turn+ ! commutator1 a %>p po9t$ tool %\ld be us$ ) a v f9e fe$4 ,a broad nos$ tool ought n to be us$1 z x is liable to burr ov] ! segm5ts4 ,aft] turn+1 ! commutator %\ld be lightly fil$ ) a dead smoo? file1 & f9ally poli%$ ) co>se & f9e s&pap]4 ,aft] ! commutator has be5 turn$ & poli%$1 ! insulation betwe5 ! segm5ts %\ld be lightly scrap$ ) ! tang ( a small file to remove any p>ticles ( metal or burrs :i* might %ort circuit ! commutator4 ,! po9ts :]e ! armature wires are sold]$ to ! lugs %\ld also be c>efully clean$ ) a bru%1 & %\ld !n receive a coat or two ( %ellac v>ni%4 ,:ile ! commutator is be+ turn$1 c>e %\ld be tak5 t ! sett+ m>ks = ! adju/m5t ( ! bru%es are n turn$ out if ^! be pres5t4 ,! same c>e %\ld be us$ 9 putt+ ! armature back into ! armature *amb] z 0 us$ 9 tak+ x out1 o!rwise ! insulation may be damag$4 ,illu/ration3 ,figs4 #gai & #gbj4--;,bissell commutators4 ,! segm5ts are ( h>d drawn copp] & are insulat$ f ea* o!r & f ! %ell by mica4 ,ques4 ,%\ld ! commutator be run )\t any lubricant8 ,ans4 ,9 mo/ cases x w be f\nd t a little lubricant is ne$$ 9 ord] to prev5t cutt+ ! bru%es1 cutt+ ! commutator2 ?is is especially ! case :5 h>d /rip bru%es are us$4 ,! quantity ( oil appli$ %\ld be v small2 a few drops sme>$ ^u a piece ( clean rag1 & appli$ to ! commutator :ile runn+1 be+ q suffici5t4 ,ques4 ,:at k9d ( oil %\ld be us$ on ! commutator8 ,ans4 ,m9]al oil1 su* z vasel9e1 or any o!r hydroc>bon4 ,animal or vegetable oils %\ld be avoid$1 z !y h a t5d5cy to c>bonize1 & ?us cause %ort circuit+ ( ! commutator1 ) att5dant sp>k+4 ,illu/ration3 ,figs4 #gba to #gbc4--,me?od ( repair+ a l>ge hole burn$ 9 two adjac5t b>s ( a commutator4 ,fig4 #gba %[s ! hole4 ,! fir/ op]ation is to clean c>efully & t9 ! surface ( ! hole4 ,! two b>s are !n w$g$ ap>t & mica /rips1 ,a ,b1 fig #gbb1 ( ! requisite size & ?ickness =c$ 94 ,! commutator mu/ n[ be w>m$ up z mu* z possible by means ( sold]+ irons1 & /rips ( mica1 ,c ,d1 ,e ,f1 fig4 #gbc1 plac$ at ! front & back ( ! hole1 be+ kept 9 position by pieces ( wood ,w1 sold] is p\r$ into ! hole f a ladle1 us+ a r\gh mica funnel to guide x4 ,ov]load ( ,dynamo4--,x may happ51 ?r\gh "s cause or o!r t a great] output is tak5 f ! ma*9e ?an x c safely c>ry4 ,:5 ?is is ! case1 ! fact is indicat$ by excessive sp>k+ at ! bru%es1 great heat+ ( ! armature & o!r p>ts ( ! dynamo1 & possibly by ! slipp+ ( ! belt 7if x be a belt driv5 ma*9e71 result+ 9 a noise4 ,! causes mo/ likely to produce ov]load are3 #a4 ,excessive voltage2 #b4 ,excessive curr5t2 #c4 ,rev]sal ( pol>ity ( dynamo2 #d4 ,%ort circuits or gr\nds 9 dynamo1 or ext]nal circuits4 ,ques4 ,:at is ! indication ( excessive voltage8 ,ans4 ,x is indicat$ by ! voltmet]1 or by ! brilliancy ( ! pilot lamp4 ,illu/ration3 ,fig4 #gbd4--,me?od ( smoo?+ commutator ) a /one4 ,! prop] /one to use is made out ( :ite s&/one simil> to t us$ = gr9d/ones1 b a trifle s(t]4 ,x is dove-tail$ into a hold]1 z %[n 9 ! illu/ration1 & held 9 place by a set screw4 ,:5 be+ us$1 "o knob is grasp$ 9 "o h& & ! o!r knob 9 ! o!r h&1 ! /one be+ mov$ back & =? along ! l5g? ( ! commutator4 ,z ! /one w become coat$ ) copp] at fir/1 x mu/ be clean$ frequ5tly by means ( co>se s&pap]4 ,! f9e du/ f ! /one w get "u ! bru%es & we> !m to a v close fit4 ,aft] us+ ! /one1 f9i% ) f9e s&pap]4 ,ques4 ,:at are ! causes ( excessive voltage8 ,ans4 ,ov] excitation ( ! field magnet or too high spe$4 ,9 ! =m] case1 resi/ance %\ld be introduc$ into ! field circuit to dim9i% ! curr5t fl[+ !re9 if a %unt ma*9e2 or if a s]ies ma*9e1 a portion ( ! curr5t %\ld be %unt$ across ! field coils by means ( a resi/ance arrang$ 9 p>allel ) ! s]ies coils2 or ! same effect may be produc$ 9 bo? cases by r$uc+ ! spe$ ( ! armature if ?is be possible4 ,if due to excessive spe$1 :i* w be indicat$ by a spe$ indicator1 ! natural rem$y is to r$uce ! spe$ ( ! eng9e driv+ ! dynamo1 or1 if ?is be n easily done1 ins]t resi/ance into ! dynamo circuit1 z describ$ above4 ,ques4 ,:at are ! causes ( excessive curr5t8 ,ans4 ,if ! dynamo be supply+ arc lamps1 ! excessive curr5t may possibly be caus$ by ! bad fe$+ ( ! lamps4 ,if ?is be ! case1 ! fact w be indicat$ by ! oscillations ( ! ammet] ne$le1 & ! un/ead9ess ( ! light4 ,if inc&esc5t lamps be 9 ! circuit1 ! fault may be caus$ by !re be+ m lamps 9 circuit ?an ! dynamo is design$ to c>ry4 ,"u su* circum/ances1 ano!r dynamo %\ld be swit*$ into circuit 9 p>allel1 or1 if ?is be n possible1 lamps %\ld be swit*$ (f until ! defect is rem$i$4 ,:5 motors are 9 ! circuit1 sp>k+ frequ5tly results at ! dynamo commutator1 ow+ to ! fluctuat+ load4 ,9 su* cases ! bru%es %\ld be adju/$ to a position at :i* ! lea/ sp>k+ occurs ) ! av]age load4 ,ques4 ,:at may be said ) respect to rev]sal ( pol>ity ( dynamos8 ,ans4 ,:5 comp\nd or s]ies w\nd dynamos are runn+ 9 p>allel1 _! pol>ity is occasionally rev]s$ :ile /opp+ by ! curr5t f ! ma*9es at "w4 ,loose ,connections1 ,t]m9als1 etc4--,:5 any ( ! connect+ cables1 t]m9al screws1 etc41 secur+ ! diff]5t circuits are loose1 sp>k+ at ! bru%es1 z a rule1 results1 = ! reason t ! vibration ( ! ma*9e t5ds to cont9ually alt] ! resi/ance ( ! v>i\s circuits to :i* !y are connect$4 ,:5 ! connections are excessively loose1 sp>k+ also results at _! po9ts ( contact1 & by ?is indication ! faulty connections may be readily detect$4 ,:5 ?is sp>k+ at ! contacts is abs5t1 ! :ole ( ! connections %\ld be c>efully exam9$ & te/$4 ,breaks 9 ,armature ,circuit4--,if !re be a brok5 circuit 9 ! armature1 z sometimes happ5s ?r\gh a fracture ( ! armature connections1 etc41 !re w be s]i\s fla%+ or sp>k+ at ! bru%es1 :i* _c be suppress$ by adju/+ ! rock]4 ,z a rule x results 9 ! production ( flats ^u "o or m b>s ( ! commutator4 ,illu/ration3 ,fig4 #gbe4--,s&pap] hold] = commutator4 ,! s&pap] is made fa/ on top by a clamp & screw4 ,! two face blocks are pivot$ & adju/ !mselves to ! commutator1 & w fit any size ( commutator4 ,if x h f\r bru%es1 ! l[] block w g 9 betwe5 ! bru%-hold]s4 ,ques4 ,h[ may su* sp>k+ be r$uc$ )\t /opp+ ! ma*9e8 ,ans4 ,by plac+ "o ( ! bru%es ( ea* set a little 9 advance ( ! o!rs1 s z to bridge ! gap4 ,%ort ,circuits 9 ,armature ,circuit4--,?is fault is indicat$ by sp>k+ at ! commutator1 & 9 bad cases by an excessive heat+ ( ! armature1 dimm+ ( ! light & slipp+ ( ! belt1 & 9 ! case ( a drum armature1 by a sudd5 cessation ( ! curr5t4 ,illu/ration3 ,fig4 #gbf4--,s&pap] block4 ,x is made to fit ! surface ( ! commutator4 ,at ,s is a saw cut into :i* ! ends are pu%$ aft] be+ wrapp$ ar\nd ! block4 ,! latt] %\ld be cut d[n on ! dott$ l9es to =m a h&le4 ,%ort ,circuits or ,breaks 9 ,field ,magnet ,circuit4--,ei!r ( ^! faults is liable to give rise to sp>k+ at ! commutator4 ,if "o ( ! coils be %ort circuit$1 ! fact w be indicat$ by ! faulty coil rema9+ cool :ile ! p]fect coil is ov]heat$4 ,! fault may arise ?r\gh "s ( ! connections to ! coils mak+ contact ) ! frame ( ! ma*9e or ) ea* o!r4 ,to asc]ta9 ?is1 exam9e all ! connections1 & te/ ) a batt]y & galvanomet]4 ,a total break 9 "o or m ( ! field coils may readily be detect$ by means ( ! batt]y & galvanomet]4 ,a p>tial break is n1 h[ev]1 s readily discov]$1 = ! reason t ! coil wires may be 9 suffici5tly close contact to give a deflection ( ! galvanomet] ne$le4 ,! only me?ods ( detect+ ?is fault is by measur+ ! resi/ance ( ! coils ) an ohmmet] or ,:eat/one bridge1 or by plac+ an ammet] 9 circuit ) ea* coil 9 turn1 & comp>+ ! am\nt ( curr5t fl[+ 9 ea*4 ,if ! p>tial break be n accessible1 ! only way to rem$y ! fault is to rew9d ! coil1 & ! same applies to a break 9 ! int]ior ( ! coil4 ,%ort ,circuits 9 ,commutator4--,^! are ( frequ5t occurr5ce1 & result 9 heat+ ! armature & sp>k+ at ! bru%es4 ,!y are caus$ ei!r by metallic du/ or p>ticles lodg+ 9 ! insulation betwe5 ! segm5ts1 or by ! det]ioration ( ! commutator insulation4 ,to rem$y1 ! insulation betwe5 ! segm5ts %\ld be c>efully exam9$1 & any metallic du/1 fil+s1 or burrs clean$ or scrap$ out4 ,:5 ! commutator is insulat$ ) asbe/os or pa/ebo>d 7z is (t5times ! case 9 dynamos ( ,european make71 %ort circuits v frequ5tly occur ?r\gh ! insulation absorb+ moi/ure or oil1 :i* is subsequ5tly c>boniz$ by ! sp>k+ at ! bru%es4 ,9 faults ( ?is description ! only rem$y is to expel all moi/ure f ! commutator insulation by means ( heat1 & scrape out all metallic du/ :i* may be emb$d$ 9 ! surface ( ! insulation4 ,if ?is d n effect a cure1 x w be necess>y to dig out ! insulation1 z f> z possible1 ) a %>p tool1 & drive 9 new insulation4 ,oil %\ld n be us$ on commutators insulat$ ) ^! mat]ials1 b only asbe/os du/ or ,fr5* *alk4 ,,*apt] ,,xxxiv ,,heat+ ,! excessive heat+ ( ! p>ts ( dynamos & motors is probably ! mo/ frequ5t & annoy+ fault :i* arises 9 op]ation4 ,:5 ! ma*9e heats1 x is a common mi/ake to suppose t any "p f\nd to be hot is ! seat ( ! tr\ble4 ,hot be>+s may cause ! armature or commutator to heat1 or vice v]sa4 ,all p>ts ( ! ma*9e %\ld be te/$ to asc]ta9 :i* is ! hotte/1 s9ce heat g5]at$ 9 "o "p is rapidly diffus$4 ,?is is be/ done by />t+ ) ! ma*9e cold2 any s]i\s tr\ble f heat+ is usually p]ceptible aft] a run ( a few m9utes at full spe$ ) ! field magnets excit$4 ,heat+ may be due to v>i\s electrical or me*anical causes1 & x may occur 9 ! diff]5t p>ts ( ! ma*9e1 z 93 #a4 ,! connections2 #b4 ,! bru%es & commutator2 #c4 ,! armature2 #d4 ,! field magnet2 #e4 ,! be>+4 ,ques4 ,h[ is heat+ detect$8 ,ans4 ,by apply+ ! h& to ! diff]5t p>ts ( ! ma*9e if l[ t5sion1 or a !rmomet] if high t5sion1 & also by a smell ( ov]heat$ insulation1 pa9t1 or v>ni%4 ,ques4 ,:at %\ld be done if ! odor ( ov]heat$ insulation1 pa9t or v>ni% be noticeable8 ,ans4 ,x is advisable to /op ! ma*9e at once1 o!rwise ! insulation is liable to be de/roy$4 ,ques4 ,:at is ! all[able rise ( temp]ature 9 a well design$ ma*9e8 ,ans4 ,x %\ld n exce$ #hj ,fahr41 above ! surr\nd+ air1 & 9 ! case ( ! be>+s1 ?is temp]ature ought n to be rea*$ "u normal conditions ( work+4 ,if ?is limit be exce$$ aft] a run ( six h\rs or less1 x indicates a ma*9e ei!r badly design$ & probably ) ! mat]ial cut d[n to ! l[e/ possible limit ) a view to *eapness1 or "s fault or o!r :i* %\ld be se>*$ = & rem$i$ z e>ly z possible1 o!rwise ! ma*9e w probably be de/roy$4 ,ques4 ,h[ %\ld ! rise ( temp]ature be measur$8 ,ans4 ,x is n suffici5t to feel ! ma*9e ) ! h&1 b special !rmomet]s mu/ be plac$ on ! armature w9d+1 imm$iately on /opp+ ! ma*9e1 cov]+ !m ) cotton or wool to prev5t cool+4 ,read+s mu/ be tak5 at %ort int]vals1 & cont9u$ till no fur!r rise ( temp]ature is indicat$4 ,heat+ ( ,connections4--,a rise ( temp]ature ( ! connections may be due to ei!r excessive curr5t1 or bad contacts1 or bo?4 ,! t]m9als & connections w be excessively heat$ if a l>g] curr5t pass ?r\gh !m ?an !y are design$ to c>ry4 ,?is ne>ly always proce$s f an ov]load ( ! dynamo1 & if ?is be rectifi$1 ! heat+ w disappe>4 ,if ! contacts ( ! diff]5t connections ( ! dynamo be n kept ?or\ghly clean & free f all grit1 oil1 etc41 & ! connections !mselves be n tightly screw$ up1 heat+ w result1 & ! connections may ev5 become unsold]$4 ,heat+ ( ,bru%es1 ,commutator & ,armature4--,:5 heat+ occurs 9 ^! p>ts1 x may be due to any ( ! foll[+ causes3 #a1 excessive curr5t2 #b1 hot be>+s2 #c1 %ort circuits 9 armature or commutator2 #d1 moi/ure 9 armature coils2 #e1 breaks 9 armature coils2 #f1 eddy curr5ts 9 armature core or conductor4 ,illu/ration3 ,fig4 #gbg4--,v5tilat$ commutator2 sectional view %[+ air ducts4 ,air is frequ5tly circulat$ ?r\gh a commutator 9 ord] to ma9ta9 x at a suffici5tly l[ temp]ature1 suitable op5+s be+ provid$ = ?is purpose z %[n4 ,ques4 ,:at may be said ) respect to excessive curr5t8 ,ans4 ,:5 a dynamo is ov]load$1 ! temp]ature ( ! armature w rise to a dang]\s ext5t1 dep5d+ ^u ! degree to :i* ! safe capacity ( ! ma*9e is exce$$1 & heavy sp>k+ ( ! bru%es w also result4 ,if ! ov]load be n remov$1 ! insulation ( ! armature may be de/roy$4 ,ques4 ,/ate "s causes ( hot be>+s4 ,ans4 ,lack ( oil2 pres5ce ( grit or o!r =eign matt] 9 ! be>+s2 belt too tight2 armature n c5tr$ ) respect to pole pieces2 be>+s too tight2 be>+s n 9 l9e2 %aft r\gh or cut4 ,illu/ration3 ,fig4 #gbh4--,self-oil+ & self-align+ be>+4 ,! self-oil+ feature consi/s ( r+s :i* revolve ) ! %aft1 & fe$ ! latt] ) oil cont9ually1 :i* !y br+ up f ! res]voir bel[4 ,! dirt settles to ! bottom1 & ! upp] portion ( ! oil rema9s suffici5tly clean = a long "t1 aft] :i* x is drawn (f1 & a fre% supply p\r$ 9 ?r\gh holes provid$ 9 ! top4 ,^! latt] are (t5 locat$ directly ov] ! slots 9 :i* ! r+s are plac$1 s t ! be>+s c be lubricat$ imm$iately by means ( an oil cup if ! r+s fail to act or ! res]voir become exhau/$4 ,! be>+ is made self-align+ by provid+ ! be>+ prop] ) an enl>g$ c5tral portion ( sph]ical %ape1 held 9 a sph]ical seat =m$ 9 ! p$e/al by turn+1 mill+1 or by ca/+ ,babbitt or o!r fusible metal ar\nd x1 ?us all[+ ! be>+ to adju/ itself to ! exact direction ( ! %aft4 ,! upp] half ( ! box c be tak5 (f to facilitate r5ewal1 etc41 & to p]mit ! armature to be remov$4 ,ques4 ,:at is ! effect ( hot be>+s8 ,ans4 ,besides giv+ tr\ble !mselves1 ! heat may be conduct$ along ! armature %aft & core1 ?us giv+ rise to excessive heat+ ( ! armature4 ,,po9ts ,,relat+ ,,to ,,hot ,,be>+s #a4 ,use good oil2 #b4 ,see t oil cups or res]voirs are full & all oil passages cle>2 #c4 ,9 self-oil+ & spla% sy/ems :]e ! oil is us$ ov] aga91 x %\ld be kept 9 clean condition by frequ5t /ra9+2 #d4 ,keep be>+s clean & prop]ly adju/$2 #e4 ,ma9ta9 be>+s 9 good alignm5t2 #f4 ,avoid tight belts2 #g4 ,exam9e ! air gap or cle>ance betwe5 armature & pole faces & see t !y are uni=m4 ,ques4 ,:at tr\bles are enc\nt]$ ) %ort circuits 9 ! armature or commutator8 ,ans4 ,?is results 9 sp>k+ at ! bru%es1 & 9 ! heat+ ( "o or m ( ! armature coils1 & ev5 9 ! burn+ up ( ! latt] if a bad case4 ,:5 ! armature is ov]heat$1 & ! defect does n proce$ f an ov]load or ! causes m5tion$ bel[1 ! dynamo %\ld be imm$iately /opp$ & te/$ = ?is fault4 ,ques4 ,:at w happ5 ) an ov]heat$ commutator8 ,ans4 ,x w decompose c>bon bru%es & cov] ! commutator ) a black film1 :i* (f]s resi/ance & increases ! heat4 ,ques4 ,:at %\ld be done if c>bon bru%es become hott] ?an ! o!r p>ts8 ,ans4 ,use high] conductivity c>bon4 ,r$uce l5g? ( bru% by adju/+ hold] to grip bru% ne>] ! commutator4 ,re9=ce bru%es ) copp] gauze1 %eet copp] or wires1 or use "s =m ( comb9$ metal & c>bon bru%4 ,increase size or numb] ( bru% if necess>y1 s ! curr5t does n exce$ #cj amp]es p] squ>e in* ( contact4 ,bru%es heat sometimes due to too mu* friction4 ,!y %\ld n press aga9/ ! commutator m ?an is necess>y = good contact4 ,ques4 ,give "s causes = heat+ ( armature4 ,ans4 ,eddy curr5ts2 moi/ure2 %ort circuits2 unequal /r5g? ( magnetic poles2 op]ation above rat$ voltage1 & bel[ normal spe$4 ,ques4 ,:at tr\ble is enc\nt]$ ) eddy curr5ts8 ,ans4 ,consid]able heat+ ( ! :ole ( ! armature results1 :i* may ev5 ext5d to ! be>+s4 ,illu/ration3 ,fig4 #gbi4--;,eck ,man*e/] type motor4 ,x is a v small size unit & is design$ = special purposes :]e v little room is available4 ,! motor occupies a space ( #b-a_/b #d-c_/h betwe5 be>+s & develops #a_/af horse p[] at #b1jjj ,r4 ,p4 ,m4 ,! frame ( ?is motor is made ( high p]meability /eel s z to r$uce ! weight to a m9imum4 ,! armature is ( ! h& w\nd bipol> type built up ( ?9 pun*+s4 ,! armature1 aft] be+ w\nd1 is bak$ at high temp]ature = a prolong$ p]iod & !n dipp$ :ile hot 9 insulat+ v>ni%4 ,pulley is "o in* 9 diamet] & takes a #a_/d in* r\nd belt4 ,weight ( motor #e-a_/b p\nds4 ,ques4 ,h[ c ?is be ov]come8 ,ans4 ,!re is no rem$y = eddy curr5ts o!r ?an ! pur*ase ( a new armature1 or recon/ruction4 ,! fault may be detect$ by excit+ ! field magnets & runn+ ! ma*9e on op5 circuit1 ) ! bru%es rais$ (f ! commutator = "s "t1 :5 ! armature w be f\nd to be excessively heat$4 ,ques4 ,h[ does moi/ure 9 ! armature coils affect ! armature8 ,ans4 ,! effect ( ?is fault be+ to practically %ort circuit ! armature1 a heat+ ( ! latt] results4 ,9 bad cases1 /eam or vapor is giv5 (f4 ,ques4 ,:at is ! effect ( %ort circuits 9 ! armature8 ,ans4 ,x produces ov]heat+4 ,ques4 ,:at tr\ble is likely to occur :5 ! armature is n c5t]$ 9 ! armature *amb]8 ,ans4 ,a heat+ ( ! be>+s is liable to be occasion$ ?r\gh ! attractive =ces develop$ by ! c5t] ( ! armature core n be+ p>allel ) ! c5tre ( ! armature *amb] or bore1 or ?r\gh ! core be+ ne>] "o pole piece ?an ! o!r4 ,?is may result f unequal we>+ ( ! be>+s1 & !re=e ! be>+s %\ld ei!r be rel9$ or ! bolt holes ( ! be>+s readju/$1 or ! be>+s pack$ up until ! armature is correctly c5t]$4 ,ques4 ,:at happ5s 9 case ( breaks 9 ! armature coils8 ,ans4 ,?is fault results 9 local heat+ ( ! armature1 = ! reason t resi/ance is int]pos$ 9 ! pa? ( ! curr5t at ! fracture4 ,x always results 9 sp>k+ at ! bru%es1 & ! heat+ be+ conf9$ to ! neighborhood ( ! break4 ,ques4 ,:at are ! effects ( op]ation above ! rat$ voltage & bel[ normal spe$8 ,ans4 ,voltage above normal is a possible cause ( heat+1 & op]ation bel[ normal spe$ calls = an increase ( field /r5g? & r$uces ! effective v5tilation1 ?us t5d+ to cause heat+4 ,illu/ration3 ,fig4 #gcj4--;,=c$ sy/em ( lubrication z appli$ to eng9e ( ! g5]at+ set %[n 9 fig4 #ddc4 ,9 eng9es employ+ ! =c$ sy/em ( lubrication ! crank pit1 :i* is =m$ by ! columns1 is accessible ?r\gh doors 9 ! front & back ( ! eng9e4 ,! base ( ! eng9e =ms an oil tank to :i* is atta*$ a small plung] pump driv5 by an ecc5tric on ! %aft4 ,! lubricant is c>ri$ "u pressure to ! v>i\s p>ts ( ! eng9e by ! me*anism %[n 9 ! accompany+ diagram4 ,! oil is =c$ by a pump to a groove 9 ! ma9 be>+1 & a drill$ hole 9 ! %aft connects ?is groove ) ! crank p94 ,f ! crank p9 box ! oil is fur!r =c$ to ! wri/ p9 ?r\gh ! pipe runn+ along ! side ( ! connect+ rod4 ,! passage 9 ! cros%ead all[s ! oil to be =c$ f ! wri/ p9 to ! guides4 ,z ! oil is =c$ f "o be>+ to ano!r1 x is q important t ! be>+ caps be set tight1 o!rwise ! oil w escape be=e rea*+ ! la/ be>+4 ,aft] pass+ ?r\gh ! be>+s1 ! oil is collect$ 9 ! base1 /ra9$ & us$ aga94 ,! oil %\ld be free f =eign sub/ances1 & to gu>d aga9/ ! introduction ( any =eign matt]1 a /ra9]1 :i* may be tak5 out = exam9ation or clean+1 is atta*$ to ! suction valve ( ! pump4 ,an oil pressure ( f #aj to #bj lbs4 %\ld be ma9ta9$1 & may be regulat$ by adju/+ ! set screw on ! relief valve ( ! oil+ sy/em4 ,! pressure gauge ne$ n rema9 9 ! circuit cont9u\sly4 ,only m9]al oils %\ld be us$ = lubrication4 ,a heavy oil gives bett] results & prev5ts knock+ m effectively ?an ?9 oil4 ,an oil :i* has be5 f\nd to give good results1 consi/s ( two-?irds r$ eng9e oil & "o-?ird heavy cyl9d] oil4 ,z ! oil passes ?r\gh ! be>+s repeat$ly1 x gradually loses its lubricat+ prop]ties1 becom+ ?ick & gritty1 & %\ld be occasionally run ?r\gh a filt] & mix$ ) new oil4 ,! frequ5cy ( ?is *ange dep5ds on ! oil1 z well z ! numb] ( h\rs ! eng9e is 9 op]ation1 & c easily be det]m9$ by obs]vation4 ,! oil 9 ! res]voir %\ld /& ab\t #b in*es ov] ! suction & dis*>ge valves1 & no wat] %\ld be all[$ to mix ) x4 ,%\ld any wat] accumulate 9 ! base1 x %\ld be drawn (f by ! cock provid$ = ! purpose be=e />t+ ! eng9e4 ,ques4 ,h[ may ! field magnets become heat$8 ,ans4 ,by excessive field curr5t2 eddy curr5t 9 pole pieces2 moi/ure2 %ort circuits4 ,ques4 ,:at may be said ) respect to excessive field curr5t8 ,ans4 ,:5 heat+ results f ?is cause1 all ! excit+ coils w be heat$ equally4 ,x may be due to excessive voltage1 9 ! case ( %unt dynamos2 or to an ov]load 9 ! case ( comp\nd & s]ies dynamos4 ,9 ei!r case x may be rem$i$ by r$uc+ ! voltage or ov]load4 ,if due to ! coils be+ incorrectly c\pl$ up1 t is1 c\pl$ up 9 p>allel in/ead ( 9 s]ies1 x w be necess>y to rectify ! connections or ins]t a resi/ance 9 s]ies4 ,ques4 ,/ate ! causes ( eddy curr5ts 9 ! pole pieces8 ,ans4 ,?is fault may be due to defective design or con/ruction ( ! armature4 ,slott$ armatures are p>ticul>ly liable to cause ?is fault1 if ! tee? & air gap be n prop]ly proportion$4 ,! defect may also be occasion$ by v>iation 9 ! /r5g? ( ! excit+ curr5t4 ,if due to ?is latt] cause1 x w be accompani$ by sp>k+ at ! bru%es4 ,if a %unt dynamo1 ins]t an ammet] into ! %unt circuit1 & note if ! deflection be /eady4 ,if ?is be n ! case1 ! v>iation 9 ! curr5t mo/ probably proce$s f imp]fect contacts ?r[n into vibration4 ,ques4 ,h[ is ! insulation affect$ by moi/ure8 ,ans4 ,moi/ure t5ds to decrease ! insulation resi/ance1 ?us 9 effect produc+ a %ort circuit ) its att5dant heat+4 ,ques4 ,h[ is moi/ure 9 ! field coils detect$8 ,ans4 ,x is easily detect$ by apply+ ! h& to ! coils1 :5 !y w be f\nd to be damp1 & 9 addition /eam or vapor w be giv5 (f :]e ! ma*9e is work+4 ,! fault may be rem$i$ by dry+ & v>ni%+ ! coils4 ,ques4 ,:at is ! indication ( %ort circuits 9 ! field coils8 ,ans4 ,?is fault is *>act]iz$ by an unequal heat+ ( ! field coils4 ,if ! coils be connect$ 9 s]ies1 ! faulty coil w be heat$ to a less ext5t ?an ! p]fect coils2 if connect$ 9 p>allel1 ! faulty coil w be heat$ to a great] ext5t ?an ! p]fect coils4 ,! =m] c ?us be easily locat$4 ,,*apt] ,,xxxv ,,op]ation ,,( ,,motors ,9 op]at+ motors ( any consid]able size1 :e!r connect$ to ! public supply ma9s ( a c5tral g5]at+ /ation = comb9$ light+ & p[] s]vice1 or to p[] s]vice ma9s only1 !re are c]ta9 precautions to be obs]v$ 9 />t+1 /opp+1 & regulat+ ! motor1 9 ord] t ! effici5cy ( ! supply1 & indirectly ! work+ ( o!r motors & lamps connect$ to ! ma9s 9 ! imm$iate neighborhood1 may n be affect$ by abnormal v>iations ( pressure4 ,^! precautions %\ld be obs]v$ also to prev5t any dang] ( ! motor itself be+ subject$ to detrim5tal me*anical %ocks & excessive temp]atures 9 ! work+ p>ts4 ,be=e ,/>t+ a ,motor4--,! g5]al in/ructions relat+ to inspection & adju/m5t1 lubrication1 etc41 :i* h already be5 giv51 %\ld be c>efully foll[$ prep>atory to />t+,e4 ,e ,,note4--,9 />t+ a motor1 fir/ see t ! be>+s conta9 suffici5t oil & t ! bru%es be> ev5ly on ! commutator4 ,if a circuit break] be us$1 close x2 !n close ! ma9 swit*4 ,rotate sl[ly ! h&le ( ! />t+ rheo/at z f> z x w g4 ,c>e %\ld be tak51 9 />t+ ! motor1 t ! h&le ( ! rheo/at be n rotat$ too fa/4 ,to /op a motor1 op5 ! circuit break] or swit*1 :i* w cut 9 ! resi/ance ( ! />t+ box4 ,nev] attempt to /op a motor by =cibly pull+ op5 ! />t+ box1 ,disreg>d ( ^! in/ructions may cause burn+ out ( ! field coils4 ,/>t+ a ,motor4--,9 />t+ a motor1 resi/ance mu/ be put 9 s]ies ) ! armature because1 s9ce !re is no rev]se electromotive =ce to c\nt]act ! appli$ voltage :5 ! motor is at re/1 ! swit*+ ( ! latt] direct to ! motor w\ld result 9 an abnormal ru% ( curr5t4 ,?is1 9 addition to be+ uneconomical & productive ( a drop ( voltage 9 ! ma9s1 w\ld injure all except ! smalle/ motors4 ,h5ce motors above two horse p[] usually require a rheo/at4 ,ques4 ,describe a rheo/at or />t+ box4 ,ans4 ,x consi/s ess5tially ( a suitable resi/ance to be ins]t$ at />t+ to r$uce ! initial ru% ( curr5t1 & :i* c be cut out 9 sections by successive movem5ts ( a lev] z ! spe$ increases4 ,illu/ration3 ,fig4 #gca4--,press = =c+ on & remov+ a commutator4 ,small commutators are press$ on to ! %aft by a h& press4 ,all ( ! l>g] commutators are press$ on by means ( a p[] press4 ,9 ! above figure is %[n a h& press4 ,! plate ,b is us$ 9 remov+ old commutators4 ,x is plac$ back ( ! commutator z at x y ) ! slot ,c ov] ! %aft4 ,bolts a b are pass$ ?r\gh ! holes 9 ! plate & secur$ by nuts4 ,! commutator c !n be =c$ (f ! %aft4 ,9 press+ on a commutator1 a sleeve is plac$ ov] ! %aft at ,o1 & aga9/ ! commutator4 ,! re> end ( ! %aft is secur$ s x w )/& ! pressure1 & ! commutator is =c$ on4 ,! p[] presses are built on ! pr9ciple ( a hydraulic press4 ,9 press+ on a commutator a piece ( babbitt metal or s(t brass %\ld be us$ aga9/ ! end ( ! %aft4 ,! %aft %\ld be pa9t$ ) :ite lead be=e hav+ ! commutator press$ on1 9 ord] to lubricate ! %aft s t ! commutator w press on easily4 ,! wip] r+s are press$ on aft] ! commutator & !n ! armature is ready to be connect$4 ,ques4 ,describe :at occurs 9 />t+ a motor4 ,ans4 ,:5 ! lev] ( ! />t+ box is mov$ to ! fir/ contact "s ( ! resi/ance is cut out ( ! circuit & curr5t fl[s ?r\gh ! motor4 ,?is produces a torque & />ts ! armature rotat+4 ,! movem5t ( ! armature induces a rev]se voltage1 :i*1 z ! spe$ increases1 gradually r$uces ! appli$ curr5t4 ,) ?is r$uction ( curr5t1 ! torque is r$uc$ & ! spe$ n accel]at$ z quickly z at fir/4 ,:5 ! appli$ curr5t has be5 r$uc$ to a c]ta9 value by ! increas+ rev]se curr5t1 ! h&le ( ! />t+ box is mov$ to ! next contact1 & s on till all ! resi/ance 9 ! />t+ box has be5 cut out1 ! motor !n atta9+ its normal spe$4 ,illu/ration3 ,figs4 #gcb to #gce4--,v>i\s />t+ resi/ances4 ,! type ( resi/ance us$ 9 motor />t+ rheo/ats ( small size consi/s usually ( t9n$ iron wire w\nd on asbe/os tubes1 z %[n 9 fig4 #gcb1 ! tubes be+ firmly support$ by porcela9 nipples1 ! ends ( :i* fit into holes 9 ! top & bottom ( ! enclos+ case4 ,9 />t]s ( l>g] size1 ca/ metal grids1 z %[n 9 fig4 #gcc1 are us$4 ,9 addition to ^! types ( resi/ance1 "s =ms ( />t] are equipp$ ) :at is kn[n z unit type resi/ance4 ,9 ?is =m1 ! resi/ance is built up ( a numb] ( sep>ate sections1 or units1 :i* are connect$ to =m ! complete />t+ or regulat+ resi/ance z ! case may be4 ,a s+le unit consi/s ( a m\ld$ core ( vitre\s mat]ial ^u :i* is w\nd ! resi/ance wire1 z %[n 9 fig4 #gcd4 ,! surface ( ! unit is !n coat$ ) a special cem5t & bak$4 ,by ?is me?od ! resi/ance mat]ial is protect$ f me*anical injury & is also made pro( aga9/ moi/ure & o!r conditions :i* sometimes affect ! ord9>y type ( resi/ance4 ,9 addition to units coat$ ) cem5t only1 !re are /ill o!r types ( units1 z 9 fig4 #gce1 :i* are provid$ ) a %eet metal cov]+ ar\nd ! cem5t1 z a fur!r precaution aga9/ injury4 ,ea* ( ! v>i\s types ( resi/ance describ$ possesses c]ta9 *>act]i/ics n %>$ by ! o!rs1 ! use ( any p>ticul> type be+ l>gely gov]n$ by conditions ( s]vice4 ,ques4 ,:at is ! diff]5ce betwe5 a />t+ box & a spe$ regulator8 ,ans4 ,motor />t+ rheo/ats or />t+ boxes1 are design$ to />t a motor & br+ x gradually f re/ to full spe$4 ,!y are n int5d$ to regulate ! spe$ & mu/ n be us$ = su* purpose4 ,failure to obs]ve ?is caution w result 9 burn+ out ! resi/ance :i*1 9 a motor />t]1 is suffici5t to c>ry ! curr5t = a limit$ "t only1 :]eas 9 ! case ( spe$ regulators suffici5t resi/ance is provid$ to c>ry ! full load curr5t cont9u\sly4 ,illu/ration3 ,fig4 #gcf4--,view ( ,cutl]-,hamm] />t] ) slate front remov$ %[+ op5 wire coil resi/ance4 ,! type ( resi/ance "h us$ consi/s ( t9n$ iron wire w\nd on asbe/os tubes4 ,! bottom ( ! cas+ is p]=at$ to secure v5tilation4 ,ques4 ,= :at k9ds ( s]vice are spe$ regulators us$8 ,ans4 ,9 cases :5 ! spe$ mu/ be v>i$1 z 9 traction motors1 organ bl[]s1 ma*9e tool drive1 etc4 ,ques4 ,h[ long does x take to />t a motor8 ,ans4 ,usually f five to t5 seconds4 ,ques4 ,h[ is ! />t+ lev] op]at$8 ,ans4 ,x is mov$ progressively f contact to contact1 paus+ long en\gh on ea* contact = ! motor to accel]ate its spe$ be=e pass+ to ! next4 ,ques4 ,:at are ! conditions at />t+ 9 a s]ies motor8 ,ans4 ,!re is a ru% ( curr5t1 ! magnitude ( :i* dep5ds on ! am\nt ( resi/ance cut out at ea* movem5t ( ! />t+ lev]4 ,illu/ration3 ,figs4 #gcg & #gch4--,slid+ contact />t]s4 ,fig4 #gcg1 />t] ) button contacts2 fig4 #gch1 />t] ) r5ewable contacts4 ,motor />t]s 9 :i* ! successive /eps ( resi/ance are cut out by a pivot$ lev] c>ry+ a contact %oe :i* slides ov] button contacts or ov] contact segm5ts1 are kn[n z slid+ contact />t]s4 ,button contacts are usually furni%$ ) motor />t+ rheo/ats ( small size :ile contact segm5ts are us$ on ^? ( great] capacity4 ,! contact segm5t be+ held 9 position by two screws1 is readily r5ewable :5 worn by long s]vice or damag$ by arc+4 ,! fix$ button contact is n s easily r5ew$ b be+ us$ only on small size />t]s is nev] likely to be subject$ to sev]e s]vice4 ,"s />t]s1 h[ev]1 h r5ewable button contacts4 ,ques4 ,h[ are small s]ies motors />t$ on batt]y circuits8 ,ans4 ,by simply clos+ a swit* to complete ! circuit1 ! resi/ance ( ! batt]y be+ suffici5t to prev5t a great ru% ( curr5t :ile />t+4 ,ques4 ,h[ is a %unt motor />t$8 ,ans4 ,9 />t+ a %unt motor1 no tr\ble is likely to occur 9 connect+ ! field coils to ! circuit4 ,s9ce ! resi/ance ( ! armature is v l[1 x is necess>y on con/ant voltage circuits to use a />t+ rheo/at 9 s]ies ) ! armature4 ,! necess>y connections are %[n 9 fig4 #gef4 ,! swit* is fir/ clos$ ?us s5d+ curr5t ?r\gh ! field coils1 be=e any passes ?r\gh ! armature4 ,! rheo/at lev] ,p is !n mov$ to ! fir/ contact to all[ a mod]ate am\nt ( curr5t to pass ?r\gh ! armature4 ,! resi/ance ( ! rheo/at is gradually cut out by fur!r movem5t ( ! lev] ,p1 ?us br++ ! motor up to spe$4 ,illu/ration3 ,figs4 #gci & #gdj4--,multiple swit* />t]s4 ,fig4 #gci1 />t] ) no voltage release2 fig4 #gdj1 />t] ) no voltage release & circuit break]4 ,! multiple swit* type ( />t] is design$ to ov]come ! arc+ on slid+ contacts :i*1 9 ! case ( l>ge motors w\ld be v sev]e4 ,! cutt+ out ( ea* /ep ( resi/ance is accompli%$ 9 ! multiple swit* />t] by a sep>ate c>bon contact swit* :i* breaks ! circuit ) a quick snappy action4 ,ques4 ,h[ does ! rev]se voltage affect ! />t+ ( a motor8 ,ans4 ,:5 a motor is /&+ /ill1 !re is no rev]se voltage1 & ! curr5t tak5 at fir/ is gov]n$ pr9cipally by ! resi/ance ( ! circuit4 ,if ! motor be s]ies w\nd1 !re is a mom5t>y rev]se voltage1 due to self-induction :ile ! field is build+ up4 ,if ! motor be %unt w\nd1 self-induction delays ! curr5t ?r\gh ! field coils1 b t ?r\gh ! armature is n imp$$ by su* cause4 ,:5 ! armature beg9s to revolve1 rev]se voltage is develop$ :i* increases ) ! spe$4 ,! resi/ance ( ! />t+ box may be gradually cut out z ! armature comes to spe$4 ,?us ! rev]se voltage gradually replaces ohmic drop 9 limit+ ! curr5t z ! motor comes to spe$4 ,illu/ration3 ,fig4 #gda4--,/>t+ rheo/at ) no voltage & ov]load release4 ,! no voltage release p]mits ! />t+ lev] to fly to ! (f position %\ld ! voltage fail mom5t>ily1 ?us protect+ ! motor aga9/ damage %\ld ! voltage sudd5ly return to ! l9e4 ,! movem5t ( ! lev] is due to a spr+4 ,! ov]load device causes ! lev] to back to ! (f position %\ld ! curr5t exce$ a pr$et]m9$ maximum = :i* ! release is adju/$4 ,fig4 #gdb4--;,comp\nd />t]4 ,rheo/ats design$ = ! d\ble duty ( />t+ a motor & regulat+ its spe$ are commonly kn[n z comp\nd />t]s1 ! resi/ance provid$ be+ a comb9ation ( armature resi/ance = />t+ duty & %unt field resi/ance = spe$ regulation4 ,failure to ,/>t4--,?is fault1 :i* is liable to occur 9 a motor ( any description1 is simil> to failure to excite 9 a dynamo1 & is liable to be produc$ by any ( ! causes m5tion$ 9 connection ) ! latt] fault1 exclud+ insuffici5t spe$1 & insuffici5t residual magnetism4 ,:5 a motor fails to />t1 x %\ld fir/ be asc]ta9$ if a supply ( electrical en]gy be available 9 ! ma9s4 ,?is may readily be discov]$ by means ( a voltmet]1 or if l[ t5sion s]vice1 by means ( ! f+]s bridg+ across ! ma9 t]m9als4 ,if ! supply ( en]gy be pres5t1 ! contact arm ( ! />t] %\ld be mov$ into su* position t all resi/ance is ins]t$ into circuit ) ! motor4 ,?is is important1 z ! motor may />t sudd5ly :ile try+ to asc]ta9 ! cause ( ! /oppage4 ,illu/ration3 ,fig4 #gdc4--,/>t+ panel4 ,9 in/all+ any k9d ( motor />t+ rheo/at1 x is necess>y to provide ma9 l9e knife swit* & fuses 9 addition to ! />t+ box4 ,! appe>ance ( ! in/allation c be mu* improv$ by m\nt+ all ( ^! ^u "o panel4 ,hav+ clos$ ! swit*1 if ! motor fail to />t1 x w be advisable to remove ! load if possible1 z ! failure may arise f an ov]load ( ! ma*9e4 ,?is be+ effect$ & ! motor n />t+1 ! t]m9als ( ! latt] %\ld be te/$ by ! means already describ$ = voltage4 ,if no voltage be g5]at$1 a brok5 circuit or a defective contact may be look$ = 9 ! ma9 fuse1 swit*1 or />t+ box4 ,! resi/ance coils ( ! latt]1 ?r\gh ! heat develop$1 frequ5tly break 9 positions out ( sight4 ,if a defective contact ( ?is nature _c readily be se51 ! contact arm %\ld be mov$ sl[ly ov] ! contacts1 z x is possible ! brok5 coil may be cut out ( circuit by ?is means4 ,illu/ration3 ,figs4 #gdd to #gdf4--;,cutl]-,hamm] motor />t+ rheo/ats ) no voltage & ov]load release4 ,fig4 #gdd1 />t] ) fix$ button contact1 fig4 #gde1 ) r5ewable button contact1 & fig4 #gdf1 ) contact segm5ts4 ,9 con/ruction ! resi/ance is enclos$ 9 a press$ /eel box on :i* is m\nt$ a m>bleiz$ slate panel c>ry+ ! />t+ lev]1 contacts & protective devices4 ,by means ( a calibrat$ scale1 ! ov]load release 7%[n 9 ! l[] left h& corn]1 figs4 #gdd & #gde1 & 9 ! l[] "r h& corn] fig4 #gdf7 c be set to break ! circuit on any ov]load n exce$+ #ej p] c5t4 ( ! rat$ capacity ( ! motor4 ,?is calibrat$ scale c also be us$ = det]m9+1 ) a fair degree ( accuracy1 ! am\nt ( curr5t be+ consum$ by ! motor4 ,if a diff]5ce ( pressure exi/ betwe5 ! motor t]m9als1 ! field magnets w1 if %unt or comp\nd w\nd & 9 good ord]1 be excit$1 :i* may be asc]ta9$ by means ( a b> ( iron4 ,if no magnetism be pres5t1 x w ( c\rse1 indicate a brok5 or bad connection1 ei!r betwe5 ! t]m9als ( ! field coils1 or "o or m ( ! coils !mselves4 ,if ! b> pull /rongly1 ! position ( ! bru%es ^u ! commutator 9 reg>d to ! neutral po9ts %\ld be asc]ta9$1 & ! rock] adju/$1 if necess>y1 to br+ !m into _! correct positions4 ,if ?is fail to />t ! motor1 ! connect+ leads f ! motor t]m9als to ! bru%es & ! bru%es !mselves %\ld be c>efully exam9$ = brok5 or bad connections1 & defective contact ( ! bru%es ) ! commutator4 ,9 ! latt] case1 x may arise f a dirty /ate ( ! commutator1 or f ! bru%es n be+ f$ prop]ly4 ,if due to ^! causes1 press+ ! bru%es d[n ^u ! commutator ) ! f+]s w probably />t ! motor4 ,if ! failure to />t arise f none ( ^! causes1 x is probably due to ! field coils act+ 9 opposition1 or to a %ort circuit$ armature4 ,?is latt] rem>k applies m especially to motors provid$ ) drum armatures4 ,illu/ration3 ,fig4 #gdg4--;,all5-,bradley compression type resi/ance units4 ,! contact resi/ance betwe5 ! discs compos+ ! resi/ance column is subject to v>iations ( pressure !reby produc+ proportionate resi/ance *anges 9 ! column z a :ole4 ,9 ! complete resi/ance unit1 ! resi/ances column is encas$ 9 a drawn /eel tube1 :i* is l9$ ) a highly refractory cem5t1 = purpose ( insulation1 af=d+ ! column bo? me*anical & electrical protection & exclud+ ! air :i* effectually prev5ts any combu/ion %\ld ! column become r$ hot due to ov]load4 ,! ends ( ! tube are clos$ by means ( caps ?r\gh :i* pass electrodes = mak+ connections betwe5 ! discs & ext]ior conductors4 ,! /eel tube1 :5 necess>y1 is provid$ ) ribs or f9s = ! dissipation ( acquir$ heat4 ,illu/ration3 ,fig4 #gdh4--;,all5-,bradley type ,z automatic motor />t]4 ,! op]ation ( ?is ma*9e is z foll[s3 ,:5 ! ma9 swit* is clos$1 ! motor circuit is made ?r\gh ! fuses1 resi/ance unit1 curr5t relay1 & ! motor armature4 ,at ! same "t1 ! sol5oid circuit is clos$ 7?is is connect$ directly across ! l9e1 & takes a curr5t :i* is a small fraction ( an amp]e71 & ! plung] ( ! sol5oid is drawn up1 :i* produces a pressure on ! resi/ance unit1 & increases ! curr5t 9 ! motor circuit to ! pr$et]m9$ value at :i* ! curr5t relay is set4 ,:5 ?is value is rea*$ ! curr5t relay op]ates & op5s ! sol5oid circuit1 :i* r$uces ! magnetic pull & all[s ! sol5oid plung] to drop back slightly4 ,?is action increases ! resi/ance 9 ! motor circuit1 :i* decreases ! curr5t suffici5tly to all[ ! relay to close aga94 ,simil> cycles ( op]ation are repeat$ z ! motor accel]ates1 & ea* "t ! plung] is drawn a little f>!r into ! sol5oid1 until ! %ort circuit+ contacts on ! top are pu%$ toge!r1 :i* %ort circuits ! curr5t relay & resi/ance unit1 mak+ !m inop]ative1 & complet+ ! op]ation ( />t+ ! motor4 ,x w be not$ t 9 />t+ a motor ) ?is device ! curr5t is always held d[n to a c]ta9 pr$et]m9$ value1 & x is impossible to ov]load ! motor by too rapid />t+4 ,! curr5t relay is calibrat$ 9 amp]es1 & may be set to suit exi/+ conditions4 ,! action ( ! />t] be+ controll$ by a curr5t relay & n by an oil or air da% pot1 ! motor w />t rapidly :5 "u a light load1 & sl[ly :5 m heavily load$4 ,! fuses or circuit break]s may be set at a value t w furni% protection to ! motor "u runn+ conditions4 ,precautions ) ,%unt ,motors4--,) motors ( ?is type1 because ( ! l>ge am\nt ( self-induction 9 ! %unt w9d+s1 x is important to note3 #a1 t 9 swit*+ on ! field magnet1 ! curr5t may take an appreciable "t to gr[ to its normal value1 & #b1 t 9 swit*+ (f1 especially ) quick break swit*es1 high voltages are induc$ 9 ! w9d+s1 :i* may break d[n ! insulation4 ,illu/ration3 ,fig4 #gdi4--,monitor />t] giv+ automatic />t ) knife swit* control2 design$ = use ) pr9t+ presses4 ,x consi/s ( a set ( sol5oids connect$ 9 s]ies & s int]op]at+ z to cut resi/ance out ( ! armature circuit ( ! motor z ! app>atus x is driv+ comes up to spe$4 ,?is type is = small motors or :]e no ne$ arises = spe$ regulation2 !re is1 !re=e1 no adju/m5t ( spe$ possible aside f an actual *ange 9 motor conditions4 ,at full spe$ ! motor is directly across ! ma9 supply l9e4 ,fig4 #gej4--,monitor automatic />t]1 equipp$ ) relay = pu% button control4 ,ques4 ,:at provision is made s t ! magnetiz+ curr5t w h "t to rea* its normal value8 ,ans4 ,! field connections are g5]ally sep>at$ f ! actual />t]1 & tak5 to ! ma9 swit*1 s t :]ev] ! ma9 swit* is clos$1 ! curr5t fl[s ?r\gh ! field coils1 be=e ! />t+ lev] is mov$4 ,ques4 ,h[ are ! connections arrang$ to avoid excessive voltage 9 ! w9d+s due to self-induction8 ,ans4 ,g5]ally ! armature & field magnet circuits are plac$ 9 a clos$ circuit t is nev] op5$4 ,9 o!r cases1 9 ord] t ! rise ( voltage may n injure ! insulation :5 ! %unt is op5$1 a special =m ( ma9 swit* is sometimes us$ :i*1 be=e break+ f ! supply1 puts a non-inductive resi/ance across ! %unt ( ! motor4 ,?is is kn[n z a fla%+ resi/ance4 ,illu/ration3 ,figs4 #gea to #gec4--,monitor control swit*es4 ,fig4 #gea1 pu% button />t & /op swit*2 fig4 #geb1 safety lev] control swit* ) sl[ & fa/ buttons = rot>y pr9t+ presses4 ,?is device w ^u pressure ( ! />t button1 set ! ma*9e 9 motion & br+ x up to ! pr$et]m9$ spe$1 ei!r z previ\sly set by ! />t] limits or by ! sett+ ( ! rheo/at arm4 ,! /op button projects "s di/ance beyond any o!r portion ( ! device1 9 ord] t 9 case ( em]g5cy ! op]ator may /op ! ma*9e m]ely by hitt+ ! face ( ! swit* ) 8 op5 h&4 ,! lev] control swit*1 fig4 #gec1 is simil> 9 its action to ! pu% button swit* b comb9es two o!r features3 lock+ po9t1 & visual indication ( ! /ation f :5ce ! press has be5 /opp$4 ,) ! lev] at ! d[nw>d position1 ! press is lock$ & _c be />t$ f any o!r /ation4 ,9 ord] to make ! press ready to />t ! lev] mu/ be rais$ to ! c5tral position4 ,?us a man may safely ent] ! press )\t delay by sett+ 8 /ation to ! lock$ position1 kn[+ t x _c be />t$ except by "s "o com+ to t /ation & realiz+ t ! press has be5 purposely lock$4 ,also1 by look+ along ! press1 x is possible to tell f :i* /ation x has be5 lock$1 & prop] action c be imm$iately tak54 ,! safety control /ation is usually comb9$ = use on l>ge rot>y presses ) ! sl[ & fa/ pu% buttons z %[n 9 fig4 #geb4 ,a pressure ^u ! fa/ or sl[ buttons w cause ! press spe$ to be correspond+ly accel]at$ or ret>d$1 & ?is action w cont9ue s long z ! button is press$4 ,! press cont9ues to run at ! spe$ atta9$ at ! in/ant ( releas+ ! button4 ,any spe$ may1 !re=e1 be select$ or *ang$ to suit mom5t>y requirem5ts4 ,?is gives complete control except+ rev]sal :i* is n requir$ ( su* a press4 ,illu/ration3 ,fig4 #ged4--,wir+ diagram ( ! /&>d =m ( ,monitor controll]4 ,a set ( sol5oids are connect$ 9 s]ies & s int]op]at+ z to cut resi/ance out ( ! armature circuit ( ! motor z ! app>atus x is driv+ comes up to spe$4 ,! controll] is design$ to be us$ on all classes ( "w4 ,9 its simple/ =m1 a s+le copp] & graphite contact1 is controll$ by two magnets1 s proportion$ z to cut out ! entire />t+ resi/ance :5 ! armature curr5t falls to a pr$et]m9$ value4 ,9 ! l>g] sizes1 ! numb] ( /eps controll+ ! resi/ance is increas$ & arrang$ to produce ! correct accel]ation4 ,9 e case ! regulation ( ! />t+ resi/ance is effect$ entirely by ! curr5t pass+ to ! motor )\t ! use ( da% pot1 me*anical gov]nor or delicate cut outs4 ,! "t elem5t is ?us directly proportion$ to ! load & ! motor br\ght up to spe$ 9 ! %orte/ "t consi/5t ) ! load1 b always ) safe limitation ( ! armature curr5t4 ,! di/9ction betwe5 ! curr5t controll$ />t] & ! />t] ) da% pot gov]nor %\ld be not$4 ,! />t] "h %[n limits ! />t+ curr5t to a fix$ value ?r\gh\t ! />t+ op]ation1 :i* is an ideal condition & prev5ts bl[+ fuses 9 />t+4 ,ques4 ,h[ c %unt motors be controll$ f a di/ant po9t8 ,ans4 ,! />t] & swit* are plac$ at ! desir$ po9t & ! two ma9 wires & ! field wires run f t po9t to ! motor4 ,?is requires additional wire :i* increases ! co/ & l9e loss4 ,regulation ( ,motor ,spe$4--,motors are g5]ally run on con/ant voltage circuits4 ,"u ^! conditions1 ! spe$ ( s]ies motors v>ies ) ! load & at light loads becomes excessive4 ,%unt motors run at ne>ly con/ant spe$s4 ,= _m purposes1 p>ticul>ly = traction1 & = driv+ tools1 x is desirable to h spe$ regulation1 s t motors runn+ on con/ant voltage circuits may be made to run at diff]5t spe$s4 ,! foll[+ two me?ods are g5]ally us$ = regulat+ ! spe$ ( motors op]at$ on con/ant voltage circuits3 #a4 ,by ins]t+ resi/ance 9 ! armature circuit ( a %unt w\nd motor2 #b4 ,by v>y+ ! field /r5g? ( s]ies motors by swit*+ sections ( ! field coils 9 or out ( circuit4 ,ques4 ,describe ! fir/ me?od4 ,ans4 ,?is me?od is illu/rat$ 9 fig4 #gef4 ,:5 ! ma9 swit* is clos$1 ! field becomes excit$1 !n by mov+ ! lev] ,p ( ! />t+ rheo/at ! v>i\s contacts 7#a1 #b1 #c1 #d1 #e71 m or less ( ! rheo/at resi/ance is cut out ( ! armature circuit1 ?us v>y+ ! spe$ correspond+ly4 ,?is is ! same z ! me?od ( />t+ a motor1 t is1 by v>iation ( resi/ance 9 armature circuit1 b x %\ld be not$ t :5 ?is me?od is us$ = spe$ regulation1 a spe$ regulat+ rheo/at %\ld be us$ in/ead ( ! ord9>y />t+ box1 because ! latt]1 n be+ design$ = ! purpose1 w ov]heat & probably burn out4 ,illu/ration3 ,fig4 #gee4--,monitor pr9t+ press controll]4 ,x provides v>iable spe$ & o!r control features requir$ 9 ! op]ation ( l>ge rot>y presses1 su* z ^? us$ = pr9t+ newspap]s4 ,f any "o ( v>i\s /ations simil> to ! "o illu/rat$ 9 fig4 #gec1 locat$ at all desirable places ab\t ! press1 ! latt] may be />t$1 /opp$1 accel]at$1 sl[$ d[n or lock$4 ,x diff]s f o!r types ( pr9t+ press controll] 9 t ! sol5oid has an ov]all maximum pull ( less ?an "o in* & does n actuate ! ma9 l9e curr5t directly b ?r\gh pilot circuits1 :i* 9 turn1 op]ate flapp] swit*es2 !re are no slid+ contacts4 ,at ! control /ations1 ! op]ator c di/+ui% ! accel]at+ button f ! ret>d+ button by ! s5se ( t\* & obvi\sly he c 9 ! same mann] asc]ta9 ! position ( ! lev]4 ,! position ( ! lev] :e!r at />t1 /op or safety1 c be readily obs]v$ at a di/ance4 ,:5 ! lev] ( ei!r control /ation is plac$ at /op1 ! curr5t is disconnect$ f ! motor & a p[]ful dynamic brake br+s ! press to re/ )\t delay & )\t %ock or h>mful /ra94 ,! />t w always be made ) all resi/ance 9 ! armature circuit1 & ) full field1 & %\ld ! curr5t supply fail1 ! controll] w release & op5 ! circuit to ! motor4 ,?is controll] w give a spe$ range z l[ z #aj ( normal spe$ by armature resi/ance &1 by field control1 any increase )9 ! spe$ ( ! motor4 ,ques4 ,describe ! second me?od4 ,ans4 ,?is me?od ( regulat+ ! spe$ ( a s]ies motor is %[n 9 fig4 #geg4 ,! curr5t ?r\gh ! armature w fl[ ?r\gh all ! field w9d+s :5 ! position ( ! swit* lev] ,s1 is on contact #d1 & ! /r5g? ( ! field w be ! maximum4 ,by mov+ ! arm to contact #c1 #b1 etc41 sections ( ! field w9d+ are cut out1 ?us r$uc+ ! /r5g? ( field & v>y+ ! spe$4 ,illu/ration3 ,fig4 #gef4--,spe$ regulation ( %unt motor by v>iable resi/ance 9 ! armature circuit4 ,ques4 ,h[ does ! spe$ v>y ) respect to v>iation ( field /r5g?8 ,ans4 ,decreas+ ! field /r5g? ( a motor increases its spe$1 :ile increas+ ! field /r5g? decreases ! spe$4 ,"u ! conditions ( maximum field /r5g?1 z ) swit* ,s on po9t #a1 ! torque w be greate/ = any giv5 curr5t /r5g? & ! rev]se voltage also greate/ at any giv5 spe$4 ,! curr5t ?r\gh ! armature ( ! motor1 to p]=m any giv5 "w1 w ?us be a m9imum1 z well z ! spe$ at :i* ! motor has to run1 9 ord] to develop suffici5t rev]se voltage to p]mit ?is curr5t to fl[4 ,regulation ( spe$ by v>y+ ! field /r5g? is limit$ 9 range ( action1 s9ce ! field saturation po9t is soon rea*$1 moreov]1 ) too l[ a field /r5g?1 armature reaction produces excessive field di/ortion1 sp>k+1 etc4 ,illu/ration3 ,fig4 #geg4--,spe$ regulation ( s]ies motor by cutt+ out sections ( ! field w9d+4 ,9 ?is me?od ! field w9d+ is tapp$ at sev]al po9ts1 divid+ ! coil into sections & ! leads f ^! po9ts are connect$ a multi-po9t swit* ( ! type t w\ld be us$ on a rheo/at4 ,by mov+ ! lev] ,s1 to ! left or "r1 ! curr5t w fl[ ?r\gh "o or m sections ( ! field w9d+1 ?us decreas+ or increas+ ! amp]e turns & !reby provid+ means ( regulation4 ,illu/ration3 ,fig4 #geh4--,spe$ regulation ( a s]ies motor by ! me?od ( %ort circuit+ sections ( ! field w9d+4 ,x w be se5 t !re are sev5 diff]5t positions = ! contact spr+s on ! b>rel contacts4 ,a4 repres5ts ! armature & bru%es1 little ,a1 ,b1 & ,c1 ! divid$ field magnet coils1 ,l ! l9e connection1 & ,g ! e>? connection4 ,! diagram %[s ! connections = trolley c> op]ation4 ,ques4 ,h[ is ! spe$ ( %unt & comp\nd motors v>i$ ) respect to ! normal spe$ 9 ! two me?ods8 ,ans4 ,! fir/ me?od 7v>iable resi/ance 9 armature circuit7 r$uces ! spe$ bel[ ! normal or rat$ spe$ ( ! ma*9e1 :ile ! second me?od increases ! spe$ above ! normal4 ,9 ! fir/ me?od ! am\nt ( spe$ r$uction dep5ds p>tly ^u ! am\nt ( resi/ance introduc$ into ! armature circuit1 & p>tly ^u ! load4 ,9 ! second me?od ! am\nt ( spe$ increase dep5ds entirely ^u ! am\nt ( resi/ance plac$ 9 ! %unt w9d+ circuit4 ,eighty-five p] c5t4 is ab\t ! maximum spe$ r$uction obta9able by armature resi/ance b s great a r$uction is seldom satisfactory s9ce comp>atively slight increases 9 ! load w cause ! motor to /all4 ,%unt field regulation may be obta9$ up to any po9t = :i* ! motor is suit$1 ! only limitation 9 ?is case be+ ! maximum spe$ at :i* ! motor may be safely op]at$4 ,x %\ld be rememb]$1 h[ev]1 t spe$ increase by %unt field weak5+ increases ! curr5t 9 proportion to ! increase 9 spe$1 & c>e %\ld be tak5 n to ov]load ! armature4 ,,note4--,a comp\nd motor may be made to run at con/ant spe$1 if ! curr5t 9 ! s]ies w9d+ ( ! field be arrang$ to act 9 opposition to t ( ! %unt w9d+4 ,9 su* case1 an increase ( load w weak5 ! fields & all[ m curr5t to fl[ ?r\gh ! armature )\t decreas+ ! spe$ ( ! armature1 z w\ld be necess>y 9 a %unt motor4 ,su* motors1 h[ev]1 are n v (t5 us$1 s9ce an ov]load w\ld weak5 ! fields too mu* & cause tr\ble4 ,if ! curr5t 9 ! s]ies field act 9 ! same direction z t 9 ! %unt fields1 ! motor w sl[ up "s :5 a heavy load comes on1 b w take c>e ( ! load )\t mu* tr\ble4 ,,note4--,motors h mu* ! same faults z dynamos1 b !y make !mselves manife/ 9 a diff]5t way4 ,an op5 field circuit w prev5t ! motor />t+1 & w cause ! melt+ ( fuses or burn+ out ( ! armature4 ,a %ort circuit 9 ! fields1 if x cut out only a "p ( ! w9d+1 w cause ! motor to run fa/] & v likely sp>k badly4 ,if ! bru%es be n set exactly opposite ea* o!r1 !re w also be bad sp>k+4 ,if !y be n at ! neutral po9t1 ! motor w sp>k badly4 ,bru%es %\ld always be set at ! po9t ( lea/ sp>k+4 ,if x become necess>y to op5 ! field circuit1 x %\ld be done sl[ly1 lett+ ! arc gradually die out4 ,a quick break ( a circuit 9 connection ) any dynamo1 or motor is n advisable1 z x is v likely to break d[n ! insulation ( ! ma*9e4 ,! ord9>y />t+ box = motors is w\nd ) comp>atively f9e wire & w get v hot if left 9 circuit long4 ,! movem5t ( ! arm f ! fir/ to ! la/ po9t %\ld n occupy m ?an ?irty seconds & if ! armature d n beg9 to move at ! fir/ po9t1 ! arm %\ld be ?r[n back & ! tr\ble locat$4 ,illu/ration3 ,fig4 #gei4--;,cutl]-,hamm] multiple swit* />t] ) no voltage release2 = use ) l>ge motors1 or ) motors ( m$ium size :]e ! />t+ conditions are sev]e or :5 m ?an fifte5 seconds are requir$ to accel]ate ! motor4 ,9 op]ation1 ! cutt+ out ( ea* /ep ( resi/ance is accompli%$ by a sep>ate lev] & ! lev]s !mselves are s int]lock$ z to prev5t clos+ swit*es except 9 prop] ord]1 beg9n+ ) ! lev] on ! left4 ,! la/ swit* 7! "o on "r h& side7 is held by an electro-magnet :5 clos$1 ea* ( ! o!r swit*es be+ held 9 ! clos$ position by a lat*+ device on ! swit* next to x4 ,9 front ( ea* swit* is plac$ a metal /op1 s arrang$ z to prev5t any swit* be+ op]at$ until ! "o next to x on ! left has be5 clos$4 ,^! metal /ops con/itute ! int]lock+ me*anism & prev5t ! />t+ ( ! motor 9 any way except by clos+ ! swit*es 9 regul> rotation1 ?us insur+ prop] resi/ance 9 ! circuit & protect+ ! motor f excessive />t+ curr5ts4 ,:5 ! curr5t is int]rupt$1 ! electro-magnet releases ! la/ swit*1 :i*1 on op5+1 releases ! lat* on ! swit* next to x1 all[+ t swit* to op51 & ?is 9 turn releases ! next lat* & s on1 ! swit*es op5+ automatically "o aft] ano!r4 ,9 />t+ ! motor1 ea* swit* %\ld be clos$ quickly & firmly1 paus+ a second or two be=e clos+ ! next swit* to give ! motor "t to accel]ate4 ,illu/ration3 ,fig4 #gfj4--;,cutl]-,hamm] spe$ regulator ) no voltage release1 regulation by armature resi/ance only1 r$uc+ spe$ ( motor bel[ normal4 ,no resi/ance 9 ! armature circuit4 ,no provision is made 9 regulators ( ?is type = increas+ ! spe$ ( ! motor4 ,! maximum spe$ obta9able :5 ^! regulators are us$ is1 !re=e1 ! normal spe$ at :i* ! motor is design$ to op]ate ) no resi/ance 9 circuit4 ,) all resi/ance 9 circuit & ! motor tak+ normal curr5t ^! regulators w r$uce ! spe$ ( ! motor #ej p] c5t4 ,if ! motor be tak+ less ?an normal curr5t ! p]c5tage ( spe$ r$uction obta9able w be correspond+ly less4 ,! not*$ fan tail ext5sion on ! l[] end ( ! lev] engages ) a magnetically op]at$ pawl to hold ! lev] squ>ely on any contact s long z ! no voltage release magnet is en]giz$4 ,ques4 ,h[ is a wide range ( spe$ regulation secur$8 ,ans4 ,by a comb9ation ( ! two me?ods4 ,regulation by ,armature ,resi/ance4--,spe$ regulators = ?is me?od ( regulation1 are design$ to c>ry ! normal curr5t on any contact )\t ov]heat+ & :5 all ! resi/ance is 9 ! circuit1 !y w r$uce ! spe$ ( ! motor ab\t #ej p] c5t4 provid$ ! motor be tak+ ! normal curr5t4 ,:5 op]at+ )\t resi/ance 9 ! armature circuit1 %unt w\nd & comp\nd w\nd motors w regulate to approximately con/ant spe$ reg>dless ( load4 ,?is *>act]i/ic ( inh]5t regulation is lo/1 h[ev]1 :5 armature resi/ance is employ$ to r$uce ! spe$ ( ! motor1 fluctuations 9 load result+ 9 fluctuations 9 spe$1 :i* become m noticeable z ! am\nt ( resi/ance ins]t$ 9 ! armature circuit is increas$4 ,accord+ly1 x becomes necess>y to move ! lev] ( ! spe$ regulator =w>d or backw>d to aga9 obta9 ! spe$ at :i* ! ma*9e 0 op]at+ be=e ! load *ang$4 ,illu/ration3 ,fig4 #gfa4--;,cutl]-,hamm] comp\nd />t] ) no voltage & ov]load release4 ,?is is a />t+ rheo/at & field regulator comb9$4 ,9 op]ation1 two lev]s are employ$1 bo? be+ m\nt$ on ! same hub po/ & "o ly+ directly "u ! o!r4 ,! upp] lev] only is provid$ ) a h&le1 b :5 mov+ f ! (f position to ! />t+ position 7t is to say1 f left to "r7 ! l[]1 or />t+1 lev] is c>ri$ along by ! upp]1 or spe$ regulat+1 lev] until x comes 9 contact ) ! no voltage release magnet :]e x is held fa/ by ! attraction ( ! magnet1 leav+ ! upp] lev] free to be mov$ backw>d ov] ! field contacts1 ?us weak5+ ! %unt field ( ! motor little by little until ! desir$ spe$ is atta9$4 ,dur+ ! op]ation ( />t+ ! motor1 ! field resi/ance is %ort circuit$ by an auxili>y contact 7! slott$ metal /rip %[n ne> c5t] ( rheo/at7 b z soon z ! />t+ lev] t\*es ! no voltage release magnet or1 9 o!r words1 :5 ! motor has be5 accel]at$ to normal spe$1 ?is %ort circuit is remov$1 & ! field resi/ance becomes effective = spe$ regulation4 ,! motor is accel]at$ f re/ to normal spe$ by mov+ bo? lev]s f left to "r1 :ile increases 9 spe$ above normal are obta9$ by mov+ ! upp] lev] f "r to left4 ,only ! l[]1 or />t+ lev] comes into contact ) ! no voltage release magnet4 ,?is lev] is provid$ ) a /rong spiral spr+ :i* t5ds always to ?r[ ! lev] back to ! (f position4 ,h5ce %\ld ! voltage fail1 ! no voltage release magnet releases ! />t+ lev] & ?is1 9 fly+ back to ! (f position1 op5s ! armature circuit ( ! motor & c>ries ! spe$ regulat+ lev] ) x to ! (f position4 ,! upp]1 or spe$ regulat+ lev]1 n be+ influ5c$ by ! spr+1 ?\gh m\nt$ on ! same hub po/ z ! />t+ lev]1 may be mov$ back & =? at w or left indef9itely 9 ! position :i* gives ! spe$ desir$4 ,:5 ! spe$ ( a motor driv+ a con/ant torque ma*9e is r$uc$ by ins]t+ resi/ance 9 ! armature circuit !re is no correspond+ r$uction 9 curr5t consum$4 ,! motor runs m sl[ly simply because a "p ( ! en]gy impell+ x is %unt$ into ! resi/ance & !re dissipat$ 9 ! =m ( heat4 ,h5ce1 :e!r ! motor be op]at+ at full spe$ or half spe$1 ! am\nt ( curr5t consum$ is ! same2 ! only diff]5ce be+ t 9 ! "o case all ! en]gy tak5 f ! l9e is exp5d$ 9 driv+ ! motor :ile 9 ! o!r case only "o half is utiliz$ = p[]1 ! o!r half be+ dissipat$ 9 ! resi/ance4 ,spe$ regulation by armature resi/ance only is !re=e op5 to two objections3 #a1 ! difficulty ( ma9ta9+ con/ant spe$ "u v>y+ load conditions1 & #b1 ! necessity ( wa/+ en]gy to secure spe$ r$uction4 ,^! objections are1 9 "p1 (fset by ! fact t spe$ r$uction by armature resi/ance may be appli$ to any motor ( /&>d design & requires no?+ m ?an ! simple/ & lea/ exp5sive spe$ regulat+ rheo/at4 ,9 cases :]e ! motor w be op]at$ ne>ly always at full spe$1 ! diff]5ce 9 fir/ co/ ( ! in/allation may ju/ify ! use ( ! armature resi/ance me?od ( control4 ,z a rule1 spe$ regulation by %unt field resi/ance is pref]able4 ,illu/ration3 ,fig4 #gfb4--;,cutl]-,hamm] comp\nd spe$ regulator ) no voltage & ov]load release2 regulation by comb9$ armature & %unt field resi/ance1 design$ to bo? decrease & increase ! spe$ ( a motor4 ,spe$ r$uction is accompli%$ by ins]t+ resi/ance 9 ! armature circuit1 ! maximum am\nt ( spe$ r$uction obta9able ) ^! controll]s be+ #ej p] c5t4 bel[ normal4 ,spe$ increase is obta9$ by ins]t+ resi/ance 9 ! %unt field circuit1 ! maximum am\nt ( spe$ increase obta9able ) ^! controll]s be+ #be p] c5t4 above normal4 ,regulation by ,%unt ,field ,resi/ance4--,s9ce regulation by ?is me?od is = spe$s above normal1 a />t] mu/ be us$ to br+ ! motor up to its rat$ spe$4 ,usually ! />t] is comb9$ ) ! regulator1 z %[n 9 fig4 #gfa1 ! device be+ call$ a comp\nd />t]4 ,illu/ration3 ,figs4 #gfc to #gfe4--;,holz]-,cabot %unt w\nd motor2 diagrams %[+ connections & positions ( index po9t = =w>d & rev]se rotation4 ,,location ,,& ,,sett+4--,! motor %\ld be plac$ 9 z cool1 clean & well v5tilat$ a location z possible1 away f acid or o!r fumes :i* w\ld attack ! metal p>ts or insulation1 & %\ld be easily accessible = clean+ & oil+4 ,d n put x 9 "s corn] :]e c>e ( motor w be neglect$ because ( ! tr\ble ( gett+ at x4 ,! motor %\ld be set s t ! %aft is level & p>allel ) ! %aft x is to drive s t ! belt w run 9 ! middle ( ! pulleys4 ,d n use a belt :i* is mu* too heavy or too light = ! "w x has to d1 z x w mat]ially r$uce ! output ( ! motor4 ,! belt %\ld be ab\t "o-half in* n>r[] ?an ! pulley4 ,,rotation4--,9 ord] to rev]se ! direction ( rotation1 int]*ange leads ,a & ,b1 & %ift bru% r+ z %[n 9 ! diagram above4 ,,susp5d$ ,,motors4--,motors ) r+ oil be>+s may be us$ on ! wall or ceil+ by tak+ (f end caps & revolv+ #ij or #ahj degrees until ! oil wells come directly bel[ ! be>+s4 ,,/>t+4--,be=e />t+ ! motor see t ! armature revolves freely1 t ! be>+s are full ( oil1 & ! oil r+s are 9 place & free to turn4 ,exam9e connections c>efully to see t !y are accord+ to above diagram1 aft] :i* proce$ z foll[s3 #a4 ,close ! ma9 knife swit*4 ,?is action %\ld n all[ any curr5t to pass ?r\gh ! motor 7see ,note #b72 #b4 ,move ! lev] ( ! />t+ rheo/at quickly & squ>ely onto ! fir/ segm5t1 & hold x !re = ab\t a second2 #c4 ,move ! lev] to ! second segm5t & hold x !re = ab\t a second2 #d4 ,move ! lev] to ! ?ird segm5t & hold x !re = ab\t a second1 & s on f "o segm5t to ! next until ! lev] has be5 mov$ ov] all ! segm5ts to ! %ort circuit position1 :]e x %\ld be held firmly by ! reta9+ magnet4 ,if ! motor d n />t :5 ! lev] ( ! />t+ rheo/at is on ! ?ird segm5t1 op5 ! ma9 knife swit* & look = ! tr\ble4 ,?is may consi/ ( any ( ! foll[+3 a4 ,wrong connections2 b4 ,too great a load on ! motor2 c4 ,! motor bru%es n 9 prop] position2 d4 ,an op5 circuit ( "s k9d2 e4 ,a %ort circuit ( "s k9d4 ,,note #a4--;,x is always advisable1 9 case ( tr\ble1 to make sure t ! fields ( ! motor are magnetiz$4 ,?is te/ is easily made by fir/ clos+ ! ma9 knife swit*1 !n mov+ ! lev] ( ! />t+ rheo/at to ! fir/ segm5t1 & f9ally hav+ an assi/ant place a screw driv] or o!r piece ( iron aga9/ ! pole pieces ( ! motor4 ,if ! fields be magnetiz$1 a heavy pull on ! iron %\ld result4 ,,note #b4--;,any possibility ( arc+ on ! fir/ contact ( ! />t+ rheo/at :5 />t+ c be obviat$ by fir/ mov+ ! lev] onto ! initial contact1 hold+ x !re1 & !n clos+ ! ma9 l9e swit*1 aft] :i* proce$ z p] p>agraphs #c & #d4 ,,to ,,/op ,,! ,,motor4--,op5 ! ma9 knife swit* & let ! />t+ rheo/at take c>e ( itself4 ,! lev] w n fly back imm$iately1 b w hold until ! motor has sl[$ d[n consid]ably4 ,,note4--,! above directions apply only to />t]s ( ! slid+ contact type4 ,,temp]atures4--,if locat$ z in/ruct$ above1 ^! motors w c>ry full load z indicat$ on ! "n plate on ! motor ) a temp]ature rise ( n ov] #dj degrees ,c5tigrade1 or #ge degrees ,fahr5heit above ! surr\nd+ air4 ,?is w feel hot to ! h& b is f> bel[ ! dang] po9t4 ,if ! motor feel too hot1 get a !rmomet] & measure ! temp]ature4 ,to d ?is1 place ! bulb ( ! !rmomet] = #aj m9utes aga9/ ! frame1 cov] ) a clo? or piece ( wa/e1 & note temp]ature z comp>$ ) t ( room4 ,if ! motor run 9 a small1 enclos$ space ) no v5tilation1 ! temp]atures w be some:at high] ?an ^? giv5 above4 ,,oil+4--,fill ! oil wells to ! ov]fl[ be=e />t+ & keep !m full4 ,use good dynamo oil4 ,be sure t ! oil r+s turn freely :ile ! motor is runn+4 ,if 9 a dirty place1 draw (f ! old fluid & fill ) new e two or ?ree mon?s4 ,,c>e ,,( ,,motor4--,! motor mu/ be kept clean4 ,if ! commutator become r\gh1 smoo? x up ) ,no4 #jj s&pap] moi/5$ ) oil4 ,:5 fitt+ new bru%es or *ang+ !m1 always s&pap] !m d[n until !y fit ! commutator p]fectly1 by pass+ to & fro b5ea? ! bru% a /rip ( s&pap]1 hav+ ! r\gh side t[>d ! bru%4 ,bru%es mu/ always be r5ew$ be=e ! metal ( ! hold] comes 9 contact ) ! commutator4 ,don't use any?+ on commutator except good m9]al ma*9e oil1 or k]os5e1 & ?is only 9 v small quantities appli$ ) a clo? hav+ no l9t or ?reads4 ,illu/ration3 ,fig4 #gff4--,sectional view %[+ pr9cipal p>ts ( ,reliance adju/able spe$ motor3 #a1 lev] fulcrum p92 #b1 lev]2 #c1 slid+ ?ru/ be>+ box2 #d1 ball be>+2 #e1 armature %aft end nut2 #f1 cap2 #g1 commutator end yoke2 #h1 lev] rod2 #i1 compression spr+2 #aj1 /eel frame2 #aa1 spe$ adju/m5t nut2 #ab1 ?ru/ coll>s & p9s2 #ac1 h& :eel rod2 #ad1 h& :eel2 #ae1 sleeve nut2 #af1 oil well cov]2 #ag1 be>+ bu%+2 #ah1 sleeve2 #ai1 oil r+2 #bj1 p9ion end yoke2 #ba1 rock] arm2 #bb1 bru% hold] /ud2 #bc1 bru%2 #bd1 commutator2 #be1 armature2 #bf1 armature lam9ations2 #bg1 armature coils2 #bh1 armature end plate2 #bi1 armature %aft2 #cj1 leads2 #ca1 axial position ( commutat+ pole2 #cb1 axial position ( ma9 field pole2 #cc1 slide rail screws2 #cd1 end yoke cap screws2 #ce1 slide rails2 #cf1 commutat+ coil2 #cg1 commutat+ pole2 #ch1 ma9 field pole2 #ci1 ma9 field coil4 ,illu/ration3 ,fig4 #gfg4--;,cutl]-,hamm] rev]sible />t] ) no voltage release1 adapt$ to />t & op]ate motor at full spe$ 9 ei!r direction1 su* = in/ance z motors driv+ auxili>y motions on la!s1 plan]s & o!r ma*9e tools :i* may rotate 9 ei!r direction b always at con/ant spe$4 ,!y are n design$ to r$uce ! spe$ ( ! motor1 b m]ely to />t x & br+ x smoo?ly up to full spe$ 9 ei!r direction4 ,two no voltage release lat*+ devices are provid$ s t ! lev] w be held 9 ! full spe$ position 9 ei!r direction s long z ! voltage ( ! l9e rema9s con/ant4 ,on failure ( voltage a /rong c5t]+ spr+ atta*$ to ! hub-po/ ( ! lev] ?r[s ! latt] to ! c5tral1 or (f position4 ,! %unt field circuit is n op5$ by />t]s ( ?is type4 ,! weak5+ ( ! %unt field ( a motor by ! ins]tion ( resi/ance 9 ! %unt field circuit causes ! armature to revolve m rapidly4 ,"o advantage ( ?is me?od ( control is t ! motor w inh]5tly regulate to approximately con/ant spe$ "u widely v>y+ load conditions4 ,ano!r advantage is f\nd 9 ! fact t all ( ! curr5t tak5 f ! l9e is utiliz$ = p[]1 ! *anges 9 spe$ be+ obta9$ n by dissipat+ a portion ( ! effective en]gy 9 ! resi/ance 7z 9 ! case ( ! armature resi/ance me?od ( control7 b by weak5+ ! rev]se voltage by ins]t+ resi/ance 9 ! %unt field circuit4 ,spe$ increase by %unt field weak5+ is limit$1 h[ev]1 to ab\t #aj to #ae p] c5t4 above ! normal spe$ 9 motors ( /&>d con/ruction4 ,great] ranges ( spe$ c be obta9$ f motors especially design$ = %unt field control b %\ld n be attempt$ ) motors ( /&>d design )\t fir/ asc]ta9+ f ! manufactur] ! maximum safe spe$4 ,comb9$ ,armature & ,%unt ,field ,control4--,regulation by comb9$ armature & %unt field resi/ance is by f> ! easie/ way ( obta9+ a wide range ( spe$s4 ,rheo/ats embody+ ^! me?ods are kn[n z comp\nd spe$ regulators1 "o =m be+ %[n 9 fig4 #gfb4 ,/&>d regulators c be obta9$ giv+ a wide range ( spe$ v>iation1 & special regulators may be con/ruct$ giv+ practically any desir$ range4 ,selection ( ,/>t]s & ,regulators4--,unsatisfactory op]ation ( ^! devices is1 9 ne>ly all cases1 due to lack ( precaution 9 select+ ! prop] piece ( app>atus = ! "w to be done4 ,"o ( ! commone/ errors is to select a rheo/at ( insuffici5t capacity4 ,if ! curr5t requir$ to op]ate ! motor at full spe$ ) no resi/ance 9 circuit be great] ?an ! rat$ capacity ( ! rheo/at1 ov]heat+ ( ! resi/ance w result4 ,an increase 9 temp]ature ev5 to a po9t :]e ! h& _c be held on ! enclos+ case ne$ cause no appreh5sion1 b %\ld ! resi/ance become r$ hot x indicates t ! app>atus is be+ work$ f> beyond its capacity1 & ! load on ! motor %\ld be r$uc$ or a regulator ( great] capacity sub/itut$4 ,if ! curr5t requir$ to op]ate ! motor at full spe$ ) no resi/ance 9 circuit be less ?an ! rat$ capacity ( ! rheo/at no ov]heat+ w occur1 b x w n be possible to secure ! full #ej p] c5t4 spe$ r$uction ! rheo/at is design$ to give ) all resi/ance 9 circuit4 ,illu/ration3 ,fig4 #gfh4--,v>i\s sizes ( ,watson commutator4 ,! segm5ts are pun*$ f h>d drawn copp] /rip & are insulat$ f ea* o!r & ! core by amb] mica1 ( h>dness correspond+ to t ( ! copp] 9 ord] t ! we> ( mica & copp] may be uni=m4 ,! segm5ts are assembl$ 9 a r+ "u great pressure & are repeat$ly heat$ & tight5$1 be+ f9ally secur$ & rigidly lock$ toge!r4 ,9 ord]+ a />t] or regulator1 ! manufactur] %\ld be furni%$ ) ! foll[+ in=mation3 #a4 ,horse p[] ( motor ) :i* spe$ regulator w be us$2 #b4 ,voltage ( motor2 #c4 ,w9d+ ( motor1 :e!r s]ies1 %unt1 or comp\nd w\nd2 #d4 ,nature ( ! ma*9e :i* motor is to op]ate2 #e4 ,normal rat$ spe$ ( motor to be us$2 #f4 ,maximum spe$ at :i* x is desir$ to op]ate ! motor2 #g4 ,m9imum spe$ at :i* x is desir$ to op]ate ! motor2 #h4 ,:e!r controll] w ev] be requir$ to rev]se direction ( motor or to op]ate x 9 "o direction only2 #i4 ,if rev]sible controll] be desir$1 :e!r or n full range ( spe$ control is requir$ 9 bo? directions2 #aj4 ,:e!r ! regulator %all be equipp$ ) any ( ! foll[+ devices3 no voltage release1 ov]load release1 knife swit*1 fuses2 #aa4 ,:e!r button contacts or r5ewable contact segm5ts are pref]r$2 #ab4 ,giv+1 also1 if possible1 ! resi/ance ( ! %unt field cold1 & ! %unt field curr5t at ! maximum spe$ requir$4 ,if ?is _c be asc]ta9$1 give horse p[]1 voltage1 normal spe$1 maximum spe$ requir$1 s]ial numb] ( motor & "n ( manufactur]4 ,illu/ration3 ,fig4 #gfi4--,organ bl[] spe$ regulator2 diagram %[+ op]ation & me?od ( in/all+4 ,a cord runn+ f ! top ( ! organ bell[s passes ov] two pulleys & is !n made fa/ to ! *a9 furni%$ ) ! regulator4 ,?is *a9 passes ar\nd a %eave :i* turns on a po/ project+ f ! c5t] ( ! slate panel4 ,atta*$ to ! l[] end ( ! *a9 is a weight1 also furni%$ ) ! regulator4 ,z ! air is exhau/$ f ! bell[s ! latt] sl[ly collapses1 draw+ ! rope d[n ) x1 & 9 s do+ turns ! %eave f left to "r1 ?us cutt+ resi/ance out ( circuit & increas+ ! spe$ ( ! motor :i* pumps air into ! bell[s4 ,respond+ to ! inru% ( air1 ! bell[s exp&s1 relax+ ! t5sion on ! rope :i* is n[ pull$ 9 ! opposite direction by ! weight1 ?us turn+ ! %eave f "r to left1 cutt+ resi/ance into circuit once m & sl[+ d[n ! motor4 ,! spe$ ( ! motor is ?us automatically regulat$ by ! bell[s1 ) ! result t a practically uni=m pressure is ma9ta9$ at all times4 ,9 connection ) an organ bl[] regulator x is necess>y to in/all a sep>ate />t+ rheo/at4 ,?is is requir$ = ! reason t all organ bell[s leak4 ,dur+ ! int]missions 9 ! musical "p ( ! s]vice1 or at o!r times :5 ! bl[] is n op]at+1 ! air gradually escapes & ! bell[s settles d[n1 mov+ ! rheo/at arm to ! "r & cutt+ out resi/ance4 ,) ! motor at re/ & ! bell[s empty all ! bl[] regulator resi/ance w\ld be %ort circuit$ & x is !re=e necess>y to avoid ?r[+ ! motor directly across ! l9e :5 />t+ aga94 ,a />t+ rheo/at ) no voltage release is suitable = ?is purpose1 & %\ld be in/all$ )9 easy rea* ( ! organi/1 s t a mom5t or two be=e beg9n+ to play he c move ! lev] ( ! />t+ box & get ! motor into op]ation4 ,:]e remote control is desirable a self />t] c be sub/itut$ = ! manually op]at$ />t+ box1 9 :i* case ! entire in/allation c be controll$ by a pu% button1 or s+le ?r[ knife swit*4 ,illu/ration3 ,fig4 #ggj4--;,g5]al ,electric type ,k#g controll] ) cov] op5 %[+ con/ruction4 ,! me*anism consi/s ( a long sp9dle1 c>ry+ a numb] ( heavy brass or gun metal segm5ts1 mak+ contact = a long] or %ort] "t ) a correspond+ numb] ( spr+ contacts4 ,! sp9dle is provid$ at its upp] end ) a h&le1 & ! v>i\s contacts are made by turn+ x ?r\gh an arc ( ab\t #aej4 ,= ?is me?od a mod]ate am\nt ( resi/ance is employ$4 ,! fir/ contact jo9s bo? motors & ! full am\nt ( resi/ance 9 s]ies across ! l9e1 & z ! motors are /&+ /ill1 maximum curr5t fl[s s t !y ex]t _! full torque4 ,! mom5t !y />t to revolve1 ! curr5t t5ds to fall1 due to ! g5]ation ( a rev]se voltage2 to prev5t ?is & ma9ta9 a heavy curr5t = "s "t1 ?us obta9+ rapid accel]ation1 ! resi/ance is arrang$ s t x c be gradually r$uc$1 until at ab\t ! f\r? not* ! two motors are 9 s]ies )\t resi/ance across ! l9e4 ,to increase /ill fur!r ! spe$ 9 ! above type ( controll]1 ! s]ies fields may be %unt$1 & !n ! next /eps place ! motors 9 p>allel ) ! resi/ance4 ,spe$ ,regulation ( ,traction ,motors4--,! spe$ regulator = motors ( ?is class is call$ a controll]1 & be+ locat$ 9 an expos$ place is enclos$ 9 a metal cas+4 ,controll]s are design$ to be us$ = />t+1 /opp+1 rev]s+1 & regulat+ ! spe$ ( motors :]e "o or m ( ^! op]ations h to be frequ5tly repeat$4 ,! controll] us$ ) a s+le motor equipm5t is practically ! same z any o!r s+le motor />t+ box1 except+ t ! resi/ance has suffici5t c>ry+ capacity to be left 9 ! circuit "s "t4 ,:5 ! motor is to op]ate at full spe$ all ! resi/ance is cut out4 ,to rev]se1 a rev]s+ not* is plac$ 9 ! armature or field circuit1 b n 9 bo?4 ,ques4 ,:at provision is made to ov]come ! arc :5 ! circuit is op5$8 ,ans4 ,a magnetic field is us$ ) su* pol>ity t x bl[s out ! arc4 ,illu/ration3 ,fig4 #gga4--;,controll] ( ! ,rau* & ,lang electric vehicles4 ,x is ( ! flat radial type4 ,two movable copp] leaf contacts ( ample size make all commutations necess>y to obta9 ! v>i\s spe$s4 ,five spe$s =w>d & rev]se are provid$4 ,magnetic bl[ out coils are us$ on all controll]s design$ = #ejj volt circuits1 & on types design$ = l[] voltages requir+ m ?an #fj amp]es normal capacity4 ,! coils are w\nd ) ei!r copp] wire or flat /rips ( suffici5t capacity to c>ry full load curr5t cont9u\sly )\t undue heat+1 & aft] be+ w\nd !y are treat$ ) an insulat+ comp\nd mak+ !m moi/ure pro(4 ,ques4 ,:at provision is made to prev5t rev]sal be=e br++ ! controll] lev] to ! (f position8 ,ans4 ,controll]s hav+ sep>ate rev]s+ cyl9d]s are fitt$ ) me*anical int]locks mak+ x necess>y to place lev] 9 (f position be=e rev]s+4 ,illu/ration3 ,figs4 #ggb to #ghb4--;,diagram ( controll] connections1 illu/rat+ ! s]ies p>allel me?od ( two motor control4 ,two ,motor ,regulation4--,) a two motor equipm5t1 ! controll] becomes m complicat$ because x mu/ be arrang$ to swit* ! motors 9 s]ies or 9 p>allel1 s z to secure economy at half & full spe$4 ,! v>i\s connections ( s]ies-p>allel regulation are %[n 9 figs4 #ggb to #ghb4 ,f ^! diagrams x is se5 t ! motors are fir/ op]at$ 9 s]ies until all ! resi/ance is cut out by ! controll] 7figs4 #ggb to #ggg74 ,! next po9t on ! controll] puts ! two motors 9 p>allel ) "s resi/ance 9 ! circuit 7fig4 #ggh71 :i* resi/ance is gradually %ort circuit$ on ! rema9+ controll] po9ts1 until at full spe$ all ! resi/ance is cut out1 ! two motors rema9+ 9 p>allel 7figs4 #ggh to #ghb74 ,/opp+ a ,motor4--,if x be desir$ to /op a motor1 ! ma9 swit* is op5$4 ,z ! armature ( ! motor cont9ues to op]ate1 due to its in]tia1 x g5]ates an electromotive =ce :i* s5ds a curr5t ?r\gh ! %unt connect$ field circuit & helps to ma9ta9 ! field excitation4 ,:5 ! spe$ ( ! motor has decreas$ suffici5tly s z n to endang] ! motor %\ld ! ma9 swit* be ?r[n1 ! curr5t 9 ! s]ies magnet becomes weak5$1 & ! spr+ ?r[s back ! />t+ box arm4 ,x %\ld be not$ t 9 /opp+ a motor hav+ a />t+ box provid$ ) a no voltage release simply op5 ! ma9 swit* & d n t\* ! lev] because o!rwise1 ! self induc$ voltage ( ! field circuit may puncture ! field w9d+ or ! insulation ( ! adjo9+ wires 9 ! />t+ box4 ,,hawk9s ,,practical ,,libr>y ,,( ,,electricity ,,9 ,,h&y ,,pocket ,,=m ,,price #a ,,ea* ,!y are n only ! be/1 b ! *eape/ "w publi%$ on ,electricity4 ,ea* numb] be+ complete 9 itself4 ,sep>ate numb]s s5t po/paid to any address on receipt ( price4 ,!y are gu>ante$ 9 e way or y\r money w be return$4 ,complete catalog ( s]ies w be mail$ free on reque/4 ,,electrical ,,guide1 ,,no4 #a ,conta9+ ! pr9ciples ( ,elem5t>y ,electricity1 ,magnetism1 ,induction1 ,exp]im5ts1 ,dynamos1 ,electric ,ma*9]y4 ,,electrical ,,guide1 ,,no4 #b ,! con/ruction ( ,dynamos1 ,motors1 ,armatures1 ,armature ,w9d+s1 ,in/all+ ( ,dynamos4 ,,electrical ,,guide1 ,,no4 #c ,electrical ,in/rum5ts1 ,te/+1 ,practical ,managem5t ( ,dynamos & ,motors4 ,,electrical ,,guide1 ,,no4 #d ,di/ribution ,sy/ems1 ,wir+1 ,wir+ ,diagrams1 ,sign ,fla%]s1 ,/orage ,batt]ies4 ,,electrical ,,guide1 ,,no4 #e ,pr9ciples ( ,alt]nat+ ,curr5ts & ,alt]nators4 ,,electrical ,,guide1 ,,no4 #f ,alt]nat+ ,curr5t ,motors1 ,trans=m]s1 ,conv]t]s1 ,rectifi]s4 ,,electrical ,,guide1 ,,no4 #g ,alt]nat+ ,curr5t ,sy/ems1 ,circuit ,break]s1 ,measur+ ,in/rum5ts4 ,,electrical ,,guide1 ,,no4 #h ,alt]nat+ ,curr5t ,swit* ,bo>ds1 ,wir+1 ,p[] ,/ations1 ,in/allation & ,op]ation4 ,,electrical ,,guide1 ,,no4 #i ,telephone1 ,telegraph1 ,wireless1 ,bells1 ,light+1 ,railways4 ,,electrical ,,guide1 ,,no4 #aj ,mod]n ,practical ,applications ( ,electricity & ,ready ,ref]5ce ,index ( ! #aj ,numb]s4 ,!o4 ,audel ,co4 ,publi%]s #gb ,,fif? ,,av5ue1 ,,new ,,york