Procedure for Calibration of Ammeter:
In this method, DC potentiometer is used for measurement of voltage across a standard low resistance.
• Connect the circuit as shown in the figure, the ammeter to be calibrated is connected in series with standard resistance and regulating resistance Rg.
• By varying Rg, voltage across potentiometer (S) is measured. Before measurement potentiometer is required to be standardized. At the same time current through ammeter is also measured (I). i.e. reading of ammeter under calibration. The sub-standard or calibrated meter and meter under test are connected in series and readings are noted for corresponding currents.
• At each step, true value of ammeter is calculated as,
where, Vs = Voltage across potentiometer S = resistance of potentiometer
And the currents are compared for finding out error in ammeter.