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How to choose and use megohmmeter

time:2021/1/9   source:华天电力  reading:264 time

A megohmmeter is a measuring instrument commonly used by electricians. The megohmmeter is mainly used to check the insulation resistance of electrical equipment, household appliances or electrical circuits to the ground and between phases to ensure that these equipment, electrical appliances and circuits are working in a normal state, and to avoid accidents such as electric shock, casualties and equipment damage.


How to use megohmmeter


1. Before measurement, the power supply of the device under test must be cut off and short-circuited to ground. Never let the equipment be charged for measurement to ensure the safety of people and equipment. For equipment that may induce high voltage, this possibility must be eliminated before measurement can be performed.


2. The surface of the measured object should be clean. Reduce the contact resistance to ensure the accuracy of the measurement results.


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3. Before measurement, the megohmmeter should be subjected to an open circuit and short circuit test to check whether the megohmmeter is in good condition. That is, before the megohmmeter is not connected to the measured object, shake the handle to make the generator reach the rated speed (120r/min), and observe whether the pointer points to the "∞" position on the scale. Short-circuit the terminal "line (L) and ground (E)", slowly shake the handle, and observe whether the pointer is at the "0" position of the scale. If the pointer cannot point to the position of the finger, it indicates that the megohmmeter is faulty. It should be used after inspection.


4. When using the megohmmeter, it should be placed in a stable and firm place, and far away from large external current conductors and external magnetic fields.


5. Must be wired correctly. There are generally three terminals on the megohmmeter, of which L is connected to the conductor part insulated from the ground, and E is connected to the outer shell or ground of the measured object. G is connected to the shield of the measured object or the part that does not need to be measured. When measuring the insulation resistance, generally only use the "L" and "E" terminals. But when measuring the insulation resistance of the cable to the ground or the leakage current of the device under test is serious, the "G" terminal should be used, and the "G" Terminate the shield or shell. After the line is connected, you can turn the handle clockwise. The shaking speed should be slow and fast. When the speed reaches about 120 revolutions per minute (ZC-25 type), keep rotating at a constant speed, and read after 1 minute. Read while shaking. Cannot stop to read.


6. Place the megger in a horizontal position during the panning, and no short circuit between the end buttons is allowed when the handle is turned. Shaking the handle should be slower and faster. If you find that the pointer is pointing to zero, it means that the insulation under test may be short-circuited. At this time, you can't continue to shake the handle to prevent heating and damage to the coil in the watch.


7. The reading is complete. Discharge the device under test. The discharge method is to remove the ground wire used during measurement from the megohmmeter and short-circuit the device under test (not megohmmeter discharge).

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