The voltage range of a current meter can be extended by adding:

Question

Question

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ALP CBT 2 Electronic Mechanic Previous Paper: Held on 21 Jan 2019 Shift 1

Answer 1

We can extend the range of ammeter by keeping a shunt resistance.

Here Rm = internal resistance of the coil

Rsh = Shunt resistance

I = Required full-scale range

Im = Full scale deflection of current

As the two resistances, Rm and Rsh are in parallel, the voltage drop across the resistance is equal.

Where

‘m’ is called multiplying power

To increase the range of a voltmeter, we need to the series resistance and it is given by

Where V is the required voltmeter range

Vm is the voltmeter range

Rm is the meter internal resistance

Note:

To increase the ranges of ammeter, we need to connect a small shunt resistance in parallel with ammeters.
To increase the ranges of a voltmeter, we need to connect a high series of multiplier resistance in series with voltmeters.