Ammeter Calibration

As magnetic particle testing equipment can use thousands of amperes getting a precise reading on an ammeter for calibration can be very difficult. It is therefore necessary to employ a current shunt and check ammeter.

A shunt ammeter (a manganin resistor with precisely recorded resistance) is usually placed in parallel with the galvanometer. As current flows through the shunt the voltage drops slightly as the shunt causes minute resistance. The voltage drop through the shunt is proportional to the amount of current flowing. A voltmeter can be placed across the shunt which can be scaled to directly display the current value.

BS EN ISO 9934-3 states that the ammeters must be capable of displaying a reading within 10% of the actual applied amperage.