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Unformatted text preview: hat t he c urrent t hrough t he shunt must be t he dif f erenc e bet ween t he
t ot al c urrent (5 amps) and t he c urrent t hrough t he movement (1 mA), bec ause branc h
c urrent s add in a parallel c onf igurat ion:
http://www.allaboutcir cuits.com/vol_1/chpt_8/4.html 2/8 1/22/2014 Ammeter desig n : Dc M eter ing Cir cuits T hen, using Ohm's Law (R=E/I) in t he right c olumn, we c an det ermine t he nec essary
shunt resist anc e: Of c ourse, we c ould have c alc ulat ed t he same value of just over 100 milli- ohms (100
mΩ) f or t he shunt by c alc ulat ing t ot al resist anc e (R=E/I; 0.5 volt s/5 amps = 100 mΩ
exac t ly), t hen working t he parallel resist anc e f ormula bac kwards, but t he arit hmet ic
would have been more c hallenging: In real lif e, t he shunt resist or of an ammet er will usually be enc ased wit hin t he
prot ec t ive met al housing of t he met er unit , hidden f rom sight . Not e t he c onst ruc t ion of
t he ammet er in t he f ollowing phot ograph: T his part ic ular ammet er is an aut omot ive unit manuf ac t ured by St ewart - Warner.
Alt hough t he D'Arsonval met er movement it self probably has a f ull sc ale rat ing in t he
range of milliamps, t he met er as a whole has a range of +/- 60 amps. T he shunt resist or
providing t his high c urrent range is enc losed wit hin t he met al housing of t he met er. Not e
also wit h t his part ic ular met er t hat t he needle c ent ers at zero amps and c an indic at e
eit her a "posit ive" c urrent or a "negat ive" c urrent . Connec t ed t o t he bat t ery c harging
http://www.allaboutcir cuits.com/vol_1/chpt_8/4.html 3/8 1/22/2014 Ammeter desig n : Dc M eter ing Cir cuits c irc uit of an aut omobile, t his met er is able t o indic at e a c harging c ondit ion (elec t rons
f lowing f rom generat or t o bat t ery) or a disc harging c ondit ion (elec t rons f lowing f rom
bat t ery t o...
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This lab report was uploaded on 04/05/2014 for the course ECSE 291 taught by Professor N/a during the Winter '11 term at McGill.
- Winter '11