A.C. Voltmeter Using Full Wave Rectifier

       the a.c. voltmeter using full wave rectifier is achieved by using bridge rectifier consisting of four diodes, as shown in the Fig. 1.

        Let 10 V r.m.s. purely sinusoidal input be applied.

       Now this meter uses full wave rectifier and hence the average value of output over a cycle is same as average of the input over a cycle i.e. 9 V.
       Thus, the 10 V r.m.s. voltage is equal to 9 V d.c. for full scale deflection. Thus the pointer will deflect to 90% of full scale.

The multiplier resistance can be obtained as

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