The working principle of the megometer: There are two coils connected to the needle of the megometer: one is connected in series with the additional resistor R in the meter; the other is connected in series with the measured resistance R., and then connected together to the manual generator. When the generator is started by hand, current flows through both coils at the same time and torques in opposite directions are generated on the two coils. The watch hands flex at a certain angle depending on the combined torque of the two couples. This deviation angle is determined by the ratio of the two currents. The additional resistance is constant, so the current value only depends on the size of the resistance to be measured. Instructions for use: Before measurement, the megger should be kept in a horizontal position, hold the meter body with your left hand, and shake the rocker handle with your right hand about 120 rpm. The pointer should point to infinity (∞). , otherwise the megger is defective. Before measurement, the power supply to the electrical apparatus and circuit under test should be cut off, and the relevant components should be temporarily grounded and discharged to ensure the safety of people and the megger and the accuracy of the results. measurement. Correct wiring must be used when measuring. The megger has 3 terminals (L, E, G). When measuring the resistance of the loop to ground, the L end is connected to the exposed conductor of the loop and the E end is connected to the ground wire or metal shell when measuring the resistance d 'loop isolation, the first and; the last ends of the loop are connected to L and E respectively; cable insulation is measured when measuring resistance, to prevent leakage current on the cable surface from affecting the accuracy of themeasurement, the shielding layer of the cable should be connected to the G terminal. The flexible measuring wire coming from the megger terminal should be well insulated and a suitable distance should be maintained between the two wires and between the wire and the ground to avoid affecting the measurement accuracy. When shaking the oscillator, do not touch the terminals of the oscillator and the circuit under test with your hands to avoid electric shock. After shaking the watch, do not short the terminals to avoid damage. Do not shake the watch for too long.
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The oscillator is a manual generator. L: line end, E: ground end, G: shield end are already set at the factory. If you just shake a separate cable, the L and E ends don't matter.
The line terminal "L" of the megger should be connected to the measured phase of the equipment, the ground terminal "E" should be connected to the shell of the equipmentent and the unmeasured phase of the equipment, and the shield terminal "G" should be connected to the protective ring or insulation sheath of the cable to reduce the measurement error caused by the current of leak on the insulation surface.
Instructions for use:
Before measurement, the power supply to the equipment under test should be turned off and the device under test should be short -circuited and thrown to the ground. Never allow the equipment to be powered for measurement to ensure the safety of people and equipment. For equipment likely to induce high voltage, this possibility must be eliminated before measurements can be made.
Shake the handle so that the generator reaches the rated speed (120 rpm) and observe whether the pointer points to the “∞” position of the scale. Short circuit the “line (L) and ground (E)” terminal, slowly shake the handle and observe whether the pointer points to thea position “0” of the scale. If the pointer cannot point to the finger position, it indicates that the megger is defective. It must be inspected before use.
Reference for the above content: Baidu Encyclopedia-Megohmmeter