The Working Principle of Digital Megohmmeter

       In a manually operated digital megohmmeter, the electromagnetic induction effect is used to generate a test voltage, that is, the armature is arranged 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, and the deflection of the indicator decreases as the current increases. Therefore, the resultant torque is proportional to the voltage and inversely proportional to the current. 

       When the circuit under test is disconnected, the torque caused by the voltage coil will reach the maximum value. And the pointer shows "infinity" (infinity) means that the entire circuit is not short-circuited. And the resistance in the circuit under test is the largest. If there is a short circuit, the pointer displays "zero", indicating the "no" resistance in the circuit under test.

Based on the working principle of ohmmeter or ratio meter. Due to the magnetic field generated by the voltage and current, the megohmmeter tester will produce a deflection torque, similar to "Ohm's Law".

The torque of the megohmmeter changes with the change of V/I (Ohm's law: V = IR or R = V/I). The resistance to be measured is connected at both ends of the generator and connected in series with the deflection coil. 

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 (that is, the position of the pointer at infinity), no current is allowed to flow through the deflection coil.

2. Small resistance = large current:-If the circuit measures a small resistance, a large current is allowed to pass through the deflection coil, that is, the generated torque makes the pointer point to "zero". 

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

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