#### In the last article, we have seen about range extension of ammeters. The range of ammeters can be extended by using a shunt or current transformer. Now let us learn about the extension of the measuring range of voltmeters.

Due to difficulty in measuring high voltages with normal voltmeters, it is, therefore, necessary to bring those high values to normal values that can be measurable by voltmeters. This process is called the extension of range of voltmeter. In this, an external device is connected to the measuring instrument to increase the measuring range of the instrument.

Similar to the ammeter, the range of the voltmeter can be extended by using a multiplier or a potential transformer. Multipliers can be used for both ac and dc voltmeters, while potential transformers can be used for only ac voltmeters.

## Extension of Range of Voltmeter Using Multiplier :

#### A multiplier is basically a resistor connected in series with the voltmeter as shown below. The main function of the multiplier is to limit the flow of current through the voltmeter in such a way that the deflection of the pointer should not exceed the full-scale deflection.

#### It must ensure that the voltmeter should be connected in parallel or across two points, to measure the potential difference.

Let,- R
_{m} = Internal resistance of the meter - R
_{s} = Resistance of multiplier - I
_{m} = Full-scale deflection current of meter - V = Voltage being measured
- V
_{m} = Full deflection voltage of the meter

From the above figure,
The multiplying factor of the multiplier is the ratio of extended voltage range to be measured V to the actual sustainable voltage by the voltmeter V_{m}. If the sustainable voltage drop of the meter V_{m} = I_{m} R_{m}. Then multiplying factor m is, Hence, to extend a voltmeter range for m times. The resistance of the multiplier required is (m-1) × resistance of the meter.

_{m}= Internal resistance of the meter_{s}= Resistance of multiplier_{m}= Full-scale deflection current of meter_{m}= Full deflection voltage of the meter