Before the measurement, cut off the power supply to the device under test, connect the conductive part of the device to the ground and fully discharge to ensure safety. Electrical devices that have been measured with a digital megohmmeter must also be grounded and discharged in good time before a new measurement can be carried out.
Before measuring, check that the digital megohmmeter is in good condition, i. H. turn on the power switch before connecting the megohmmeter and digital megohmmeter to the object to be tested. Check the digital megohmmeter battery condition. If the battery of the digital megohmmeter is under voltage, the battery should be replaced in time, otherwise the measurement data will be unacceptable.
Insert the test cable into the line (L) and ground (E) terminal, select the test voltage, disconnect the test cableabel, press the test button and observe whether the display shows whether the number is infinity.
Short the Line (L) and Ground (E) terminal, press the test button and see if the reading reads 0.
If the LCD screen does not show 0, it means the digital megohmmeter is defective and should be repaired before use. Must be wired correctly. There are generally three terminals on a digital megger, labeled L (line), E (ground), and G (shield).
Among these, L is connected to the insulated conductor part of the measured object and the earth, E is connected to the sheath of the measured object or the earth, and G is connected to the shield of the measured object or the part , which does not need to be measured. Connection G is used to shield the surface current.
When measuring the insulation resistance of the cable isthe measurement result will be inaccurate due to the leakage current on the surface of the insulating material, especially in high humidity and the surface of the cable insulation is not clean. In this case, the measurement error is large.
To avoid the influence of surface currents, add a metal shield ring on the surface of the measurement object and connect it to the shield terminal of the digital megohmmeter.
In this way, the surface leakage current IB starts at the positive terminal of the generator and flows back to the negative terminal of the generator via terminal G to form a loop. The IB no longer passes through the measuring mechanism of the megohmmeter, so that the influence of the surface leakage current is basically eliminated.
The wires connected between the clamp and the device under test should not use double stranded insulated wires or twisted pair wires, but should be separated with single stranded wiresen to avoid errors due to poor insulation of the twisted wires. In order to obtain correct measurement results, the surface of the specimen should be wiped with a clean cloth or cotton gauze.
When measuring the insulation resistance of large-capacity devices, do not disconnect the megohmmeter immediately after reading, otherwise the charged capacitor will discharge the megohmmeter, which may cause the megohmmeter to burn out.
After the measurement, the test line should be disconnected first and then the test should be stopped. Before the megohmmeter and the object to be tested are fully discharged, do not touch the conductive part of the megohmmeter to the device to be tested with your hands.
When measuring the insulation resistance of the device, it should also be recorded. Temperature, humidity and related conditions are used to analyze the measurement resultsn of the specimen used during the measurement.
Choosing a digital megohmmeter is all about choosing the voltage and the measuring range. High voltage electrical equipment requires high insulation resistance and a high voltage megohmmeter must be used for testing;