The megohmmeter under UHV power can help many power workers conduct various power tests more conveniently.

In a manually operated digital megohmmeter, the electromagnetic induction effect is used to generate the test voltage, where the armature is placed in a permanent magnetic field and the electronic megohmmeter generates the test voltage. As the voltage in the external circuit increases, the deflection of the indicator increases, while the deflection of the indicator decreases with the increase of current. Therefore, the synthesized torque is directly proportional to the voltage and inversely proportional to the current.

When the tested circuit is disconnected, the torque generated by the voltage coil will reach its maximum value. The pointer displaying 'infinity' indicates that the entire circuit is not short circuited. And the resistance in the tested circuit is the highest. If there is a short circuit, the pointer displays "zero", indicating that the resistance in the tested circuit is "none".

The working principle based on an ohmmeter or ratio meter. Due to the magnetic field generated by voltage and current, the megohmmeter tester will produce a deflection torque, similar to Ohm's law.

If current is supplied to the coil, the torque generated should be in the opposite direction.

1. High resistance=no current: - If the resistance is very high (i.e. the pointer is at infinity), no current is allowed to flow through the deflection coil.

2. Small resistance=large current: - If the circuit measures small resistance, it allows large current to pass through the deflection coil, which generates torque to make the pointer point to "zero".

3. Intermediate resistance=Variable current: - If the measured resistance is intermediate, the generated torque will align or set the pointer between the "zero to initial" range.