Permanent Magnet Moving Coil Instrument (PMMC) as a D.C. Voltmeter

Permanent Magnet Moving Coil Instrument (PMMC) as a D.C. Voltmeter Points : Permanent Magnet Moving Coil Instrument (PMMC) as a D.C. Voltmeter AD. Arsonval basic meter movement is converted in to a voltmeter by connecting a series resistance with it. This series resistance is called a “multiplier”. This combination of meter and multiplier is put across the circuit, whose voltage is to be measured.

The multiplier limits the current through the meter so that it does not exceed the value for full scale deflection and thus prevents the movement from being damaged.

Let,
I_m = full scale deflection current of meter
R_m= internal resistance of meter movement
R_s= series resistance/multiplier resistance
_v = voltage across the meter movement
V = full range voltage of instrument