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Unformatted text preview: rare and expensive c omponent s
indeed. A c ust om resist or made f rom met al st oc k or t hic k wire may have t o be
c onst ruc t ed f or R1 t o meet bot h t he requirement s of low resist anc e and high power
Somet imes, shunt resist ors are used in c onjunc t ion wit h volt met ers of high input
resist anc e t o measure c urrent . In t hese c ases, t he c urrent t hrough t he volt met er
movement is small enough t o be c onsidered negligible, and t he shunt resist anc e c an be
sized ac c ording t o how many volt s or millivolt s of drop will be produc ed per amp of
c urrent : http://www.allaboutcir cuits.com/vol_1/chpt_8/4.html 5/8 1/22/2014 Ammeter desig n : Dc M eter ing Cir cuits If , f or example, t he shunt resist or in t he above c irc uit were sized at prec isely 1 Ω, t here
would be 1 volt dropped ac ross it f or every amp of c urrent t hrough it . T he volt met er
indic at ion c ould t hen be t aken as a direc t indic at ion of c urrent t hrough t he shunt . F or
measuring very small c urrent s, higher values of shunt resist anc e c ould be used t o
generat e more volt age drop per given unit of c urrent , t hus ext ending t he usable range of
t he (volt )met er down int o lower amount s of c urrent . T he use of volt met ers in
c onjunc t ion wit h low- value shunt resist anc es f or t he measurement of c urrent is
somet hing c ommonly seen in indust rial applic at ions.
T he use of a shunt resist or along wit h a volt met er t o measure c urrent c an be a usef ul
t ric k f or simplif ying t he t ask of f requent c urrent measurement s in a c irc uit . Normally, t o
measure c urrent t hrough a c irc uit wit h an ammet er, t he c irc uit would have t o be broken
(int errupt ed) and t he ammet er insert ed bet ween t he separat ed wire ends, like t his: If we have a c irc uit where c urrent needs t o be measured of t en, or we would just like t o
make t he proc ess of c urrent measurement more c onvenient , a shunt resist or c ould be
plac ed bet ween t hose point s and lef t t here permanent ly, c urrent readings t aken wit h a
volt met er as needed wit hout int errupt ing c ont inui...
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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