Calibration of PMMC Voltmeter Using a Potentiometer
Procedure for the Calibration of Permanent Magnet Moving Coil (PMMC) Voltmeter:-
- Give connections as per the circuit diagram in above figure.
- Vary the voltage across the voltmeter so that it reads a rounded position, say 5 volts.
- Measure the voltage across the voltmeter by potentiometer and tally the voltmeter indication and potentiometer reading.
- Draw the calibration curve which is drawn between % error voltage Vs measured potentiometer readings. The expected curve is as follows:
- Repeat the above steps for different voltages and tabulate the results. The expected tabular readings are given below:
|S.No||Voltmeter Reading||Pot. Reading m.f(v)||Measured Pot. Reading = [(m.f)x 30/1.5]||% error|
- Connections should always be made with due care of polarity.
- For measuring higher voltages better use a volt ratio box.
- Standardize the potentiometer at regular intervals during prolonged tests to compensate it from any slight drift in the battery voltage.