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Megohmmeter work

time:2020/6/8   source:华天电力  reading:288 time

Connect the resistance to be tested between the test terminals (L and G), then turn the generator handle steadily at a uniform speed until the pointer gives a stable reading. You can fully understand the working principle of the megohmmeter insulation tester from the following steps:

Insulation Resistance Tester.png

•step 1. When the test terminal is disconnected, the resistance to be measured is unlimited. If the generator handle rotates, the generated voltage will send current through the potential coil, and no current will flow through the current coil. Therefore, the mobile system rotates in such a direction that the pointer stops at the end of the scale at infinity.

• Step 2. If the test terminal is short-circuited and the generator is running, the generator will send a large current through the current coil, and only a small current will flow through the potential coil. Therefore, the resultant torque thus generated causes the pointer to point to the zero end of the scale.

• Step 3. If the unknown resistance to be tested is connected between the test terminals, a considerable amount of current will flow in both coils. The actual position occupied by the pointer depends on the ratio of the current in the two coils, which is the unknown resistance.

The meaning of zero sum infinity of megohmmeter

When a fist shows a zero reading, it means that the unknown resistance value being measured is very low. If zero value is displayed when measuring insulation resistance, it indicates insulation failure or short circuit.


When it displays an infinite reading, it means that the unknown resistance being measured has a very high value (or open circuit).

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