Insulation resistance tester measurement principle and method

The insulation resistance tester measures the resistance by Ohm's law by exciting the device or network under test with a voltage and then measuring the current generated by the excitation. The excellent megohmmeter calibrator includes a variety of optional resistors, which is not much different from the resistors offered by modern calibrators using the composite resistor function. The megohmmeter calibrator differs from the DC/low frequency calibrator in the range of resistors required and the ability to withstand voltages. For example, these electrical testers apply much higher voltages when making resistance measurements than ohmmeter functions on digital multimeters (DMMs).

How to use the insulation resistance tester

1. The power of the device under test must be cut off before the measurement, and the ground should be short-circuited. Never allow the device to be powered for measurements to ensure the safety of the person and equipment. For devices that may induce high voltage, the possibility must be eliminated before measurements can be made.

2. The surface of the object to be tested should be cleaned to reduce the contact resistance and ensure the correctness of the measurement results.

3. Before the measurement, the megohmmeter should be tested for open circuit and short circuit to check whether the megohmmeter is good. 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 refers to the “∞” position of the scale. Short the terminal "Line (L) and Ground (E)", slowly shake the handle to see if the pointer points to the "0" position of the scale. If the pointer cannot point to the position of the finger, it indicates that the megohmmeter is faulty and should be used after inspection.

4. The megohmmeter should be placed in a stable and stable place and away from large external current conductors and external magnetic fields.

5. Must be wired correctly. There are generally three terminals on the megohmmeter, where L is connected to the conductor and the insulated part of the earth, and E is connected to the outer casing or the earth of the object to be tested. G is connected to the shield of the object to be tested or the part that does not need to be measured. When measuring the insulation resistance, generally only the "L" and "E" ends are used. However, when measuring the insulation resistance of the cable to the ground or the leakage current of the device under test is serious, use the "G" terminal and terminate the "G" with the shield or casing. After the line is connected, turn the handle clockwise. The speed of shaking should be slow and fast. When the speed reaches 120 rpm (ZC-25 type), keep rotating at a constant speed, read after 1 minute, and read while shaking, can't stop reading.

6. When the shake is measured, the megger is placed in the horizontal position, and the handle is not short-circuited when the handle is rotated. Shake the handle should be slow and fast. If the pointer is zero, it indicates that the tested insulation may be short-circuited. At this time, the handle cannot be continuously shaken to prevent the coil inside the watch from being damaged.

7. When the reading is completed, discharge the device under test. The discharge method is to take the ground wire used for the measurement from the megohmmeter and short-circuit it with the device under test (not the megohmmeter discharge).

Calibration procedure for insulation resistance tester

1. An impedance bridge with a range of 103 to 1012 with an accuracy of 1%. High-precision relative humidity meter (Relative Humidity Hygrometer) High accuracy Thermometer

2. Open the cover and be careful not to damage the two wires connecting the power switch on the board.

3. Find the three calibration regulators at the bottom right of the board (Calibration Pots)

4. Make the watch at least 1/2 hour under this environmental condition and obtain self-balancing before starting the test.

5. Use one end of the connecting cable of the ACL-800 to connect the alligator clip and the other end of the banana plug.

6. Insert the 3.5 mm long plug into the socket of the meter.

7. Connect the ends of the resistor with an alligator clip.

8. Three calibration regulators, the uppermost is the “humidity” measurement, the middle is the “impedance”, and the bottom is the “temperature adjustment with a small screwdriver”. The clockwise direction is the increase value adjustment, and the counterclockwise direction is the decrease value adjustment.

9. Press the power switch and compare the “Temperature”, “Humidity” and “Resistance” values.

10. Release the power switch and slowly adjust the corresponding calibration regulator.

11. Press the power switch again to observe the LCD display.

12. If you need to recalibrate, press the power switch and adjust the corrector again.

13. Close the cover and tighten the four fixing screws.

14. Press the power switch to determine if the meter is working properly.