Calibration of Permanent-Magnet Moving Coil aka PMMC Ammeter

Procedure for the Calibration of PMMC Ammeter:-

Calibration of Ammeter Diagram
  1. Give the connections as per the circuit diagram.
  2. By adjusting the supply voltage make that the ammeter shows a current of 0.1 Amps
  3. Now measure the voltage across the shunt by using a potentiometer.
  4. Determine the current through the shunt by dividing potentiometer reading by shunt resistance (0-1Ω).
  5. Draw the calibrations curve which is drawn between %error Vs measured indication. The expected graph is as follows:
    Calibration of PMMC Ammeter Expected Graph
  6. Repeat the same for different current curves with the only precaution of making connections with due care of polarity and tabulate the results. The expected example results are as given in the below table.

    S.No Ammeter Reading Pot. Reading (V) Standard Resistance Measured Reading (A) % error
    1. 0.51 0.043 0.1 0.43 15.681
    2. 0.61 0.053 0.1 0.53 13.11
    3. 0.7 0.061 0.1 0.61 12.85
    4. 0.89 0.0775 0.1 0.775 12.92
    5. 1.00 0.0875 0.1 0.875 12.5

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