Lessons in practical electricity; principles, experiments, and arithmetical problems, an elementary text-book . Fig. 199.—Connections of an Ammeter with aa reduction of the Portable Shunt, shunts resistance to one-third of its original value, the rangeis increased three-fold and the readings are multiplied by advantage of an external shunt in switchboard instru-ments for power stations is, that instead of running heavycopper cables to a distant ammeter, a shunt may be insertedin the cable circuit and the two small size shunt leads wiredto the instrument, thus effecting an economy in copp
Lessons in practical electricity; principles, experiments, and arithmetical problems, an elementary text-book . Fig. 199.—Connections of an Ammeter with aa reduction of the Portable Shunt, shunts resistance to one-third of its original value, the rangeis increased three-fold and the readings are multiplied by advantage of an external shunt in switchboard instru-ments for power stations is, that instead of running heavycopper cables to a distant ammeter, a shunt may be insertedin the cable circuit and the two small size shunt leads wiredto the instrument, thus effecting an economy in copper andconstruction. A Weston ammeter may be used without itsshunt as a millivoltmeter, in which case it is quite sensitive andadapted to many electrical measurements. When resistanceis added in series with it, it becomes a long coil galvanome-ter, and may be calibrated as a direct reading voltmeter,If 180. The same mechanical construction is employed inWeston voltmeters, ^f^f 234 and 235, the only difference beingin the value of the extra resistance added and the method ofconnecting it to the 208 PRACTICAL ELECTRICITY. To measure currents larger than the capacity of an R = resistance of shunt required ;r — resistance of ammeter ;A = range of ammeter ;Ax = desired range of ammeter. Then,E = 5^xxr (57). The indicated readings obtained must be multiplied by ~l to be cor-rect. A Prob. 71-A: (1) What will be the resistance of a shunt required toincrease the capacity of an ammeter from 150 to 600 amperes? Re-sistance of the (2) What will be the multiplyingpower of the shunt ? By Formula (57) R = -~^ X r = *501KA X .009 = .003 — A 000 — 150 Multiplying power of the shunt = A1=r^ = 4, or by Formula (48) A lOO „ G, -, .009,, , QUESTIONS. 1. What is the advantage of a Weston type of ammeter over oneconstructed to actuate upon the solenoid and core principle? 2. In what respect does the Thomson inclined coil ammeter differfrom the
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