Megohmmeter

an instrument used in measuring very high electric resistance (above 10s ohms), particularly that of insulation on wires, cables, connectors, transformers, and windings of electric motors, as well as for measuring surface and volume resistance of insulating materials.

The most widely used types of megohmmeters consist of an AC generator with an operating voltage of up to 500 V, a two-frame magnetoelectric quotient meter, a scale graduated in megohms, and series resistances. The logometer frames form two parallel branches, one of which contains the resistance r_x being measured. In measuring the electric resistance of insulation with a megohmmeter, the temperature and humidity of the ambient air must be taken into account, since these conditions strongly affect the results of measurements. The measurement error is 1-5 percent; the instrument scale is nonlinear. There are also electronic and digital megohmmeters.