Ammeter design _ Dc Metering Circuits

Allaboutcir cuitscomvol1chpt84html 68 1222014 ammeter

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Unformatted text preview: t y in t he c irc uit : http://www.allaboutcir cuits.com/vol_1/chpt_8/4.html 6/8 1/22/2014 Ammeter desig n : Dc M eter ing Cir cuits Of c ourse, c are must be t aken in sizing t he shunt resist or low enough so t hat it doesn't adversely af f ec t t he c irc uit 's normal operat ion, but t his is generally not dif f ic ult t o do. T his t ec hnique might also be usef ul in c omput er c irc uit analysis, where we might want t o have t he c omput er display c urrent t hrough a c irc uit in t erms of a volt age (wit h SPICE, t his would allow us t o avoid t he idiosync rasy of reading negat ive c urrent values): sutrsso eapecrut hn eitr xml ici v 10 1 rhn 121 sut rod201k la 5 .cv 1 1 1 d 122 .rn d v12 pit c (,) .n ed v 1 120+1 .0E0 v12 (,) 799-4 .9E0 We would int erpret t he volt age reading ac ross t he shunt resist or (bet ween c irc uit nodes 1 and 2 in t he SPICE simulat ion) direc t ly as amps, wit h 7.999E- 04 being 0.7999 mA, or 799.9 µA. Ideally, 12 volt s applied direc t ly ac ross 15 kΩ would give us exac t ly 0.8 mA, but t he resist anc e of t he shunt lessens t hat c urrent just a t iny bit (as it would in real lif e). However, suc h a t iny error is generally well wit hin ac c ept able limit s of ac c urac y f or eit her a simulat ion or a real c irc uit , and so shunt resist ors c an be used in all but t he most demanding applic at ions f or ac c urat e c urrent measurement . http://www.allaboutcir cuits.com/vol_1/chpt_8/4.html 7/8 1/22/2014 Ammeter desig n : Dc M eter ing Cir cuits REVIEW: Ammet er ranges are c reat ed by adding parallel "shunt " resist ors t o t he movement c irc uit , providing a prec ise c urrent division. Shunt resist ors may have high power dissipat ions, so be c aref ul when c hoosing part s f or suc h met ers! Shunt resist ors c an be used in c onjunc t ion wit h high- resist anc e volt met ers as well as low- resist anc e ammet er movement s, produc ing ac c urat e volt age drops f or given amount s of c urrent . Shunt resist ors should be selec t ed f or as low a resist anc e value as possible t o minimize t heir impac t upon t he c irc uit under t est . Relat ed Links Worksheet : Ammet er design Worksheet : Volt met er design Worksheet : Current divider c irc uit s Worksheet : Basic ammet er use F orum: Unknown met er and short c irc uit ing F orum: Changing t he range of an Unknown Ammet er F orum: Volt met er design problem, please help F orum: Ammet er design F orum: Series resist or quest ion F orum: Shunt http://www.allaboutcir cuits.com/vol_1/chpt_8/4.html 8/8...
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