Insulation resistance tester, commonly known as megohmmeter or high resistance meter, is widely used to measure the insulation resistance of generators, motors, power transformers, wiring, electrical appliances and other electrical devices (such as control, signal, communication and power cables).
Insulation resistance tester is often used in routine maintenance program to indicate the change of insulation resistance of motor in months or years. A large change in insulation resistance may indicate a potential failure. Therefore, it is necessary to calibrate the megohmmeter regularly to ensure that the meter itself does not change with time.
The megohmmeter uses a voltage to excite the device or network under test, then measures the current generated by the excitation, and uses Ohm's law to measure the resistance. Excellent megohmmeter calibrators include a variety of optional resistors, which are not different from those provided by modern calibrators using the synthetic resistor function. The difference between the megohmmeter calibrator and the DC / LF calibrator lies in the range of resistors required and the voltage capability to withstand.