High-voltage digital megohmmeter use precautions and fault repair methods

Digital megohmmeter, also known as shaker watch, also known as insulation resistance meter, also known as electronic shaker, is mainly used for the determination of insulation resistance of high voltage or low voltage electrical lines and electrical equipment. It is easy to carry, does not require other auxiliary equipment for measurement, and can read readings directly from the dial.

Before use, check the insulation resistance meter. Before use, first place it in the horizontal position, open the end button “E” and “L”, and shake the hand-cranked generator at the rated speed of 120r/min or 150r/min. Observe whether the pointer is at infinity (∝) position, then short-circuit “E” and “L”, and shake the generator at the rated speed to see if the pointer points to zero. At the same time, it should be checked whether the generator is flexible or not. Whether the insulation resistance meter pointer is stuck or not.

First, select the appropriate insulation resistance meter according to the measurement object and its rated voltage. That is, the selected insulation resistance meter must have a rated voltage that is compatible with the operating voltage of the electrical equipment or electrical circuit to be tested. Example: Measure the insulation resistance of high-voltage equipment. Do not use insulation resistance meter with rated voltage below 500V. The measurement results at this time do not reflect the insulation resistance at the operating voltage. Therefore, care should be taken not to measure the insulation resistance of low-voltage electrical equipment with an insulation resistance meter with too high a voltage to prevent damage to its insulation. At the same time, the measurement range of the insulation resistance meter should not exceed the range of the insulation resistance to be tested.

Precautions when using:

1. The measurement of the insulation resistance must be carried out in the state of power failure of the electrical equipment or electrical circuit. In particular, equipment with large capacitance must be measured after full discharge to prevent electric shock.

2. In order to obtain accurate measurement results, the hand-cranked generator is required to operate at the rated speed for one minute before reading.

3. Before the insulation resistance meter stops rotating and the measured object is not discharged, the measuring part of the measured object cannot be touched by hand. Especially when the equipment with large capacitance is tested, the measured object must be short-circuited to the ground. Then stop turning the insulation resistance meter to prevent the capacitor discharge from damaging the insulation resistance meter.

Common faults and repairs:

1. When the end buttons "E" and "L" are open, shaking the hand of the generator generator does not mean "∝".

First remove the handle, unscrew the fastening screw, and solder the generator spring lead with a soldering iron to separate the measuring mechanism from the generator.

Inspection and measurement mechanism: The measurement mechanism mainly consists of a cross-type coil (taking the ZC25 type meter as an example), a guide wire, a voltage, and a current loop resistance.

1 Firstly, observe whether the guide wire is deformed. Because the guide wire is deformed, the residual torque increases, especially in the vicinity of “∝”. Because the magnetic field is weak, the positioning torque is small, and error is easy to occur. If so, the guide wire should be readjusted or replaced. The replacement guide wire should meet the following requirements: the guide wire is not broken, and the upper, middle and lower guide wires should be parallel and cannot be upturned or drooped. When the pointer is moved by hand from “0” to “∝”, the guide wire cannot touch the shaft or other objects.

2 Use a multimeter to measure whether the voltage coil is open or shorted. If yes, rewind or replace.

3 Check if the voltage loop resistance increases. If so, readjust the voltage loop resistance.

Check the generator:

1 Measurement of generator output voltage: Hand-cranked generator, use an electrostatic voltmeter or high-voltage digital voltmeter to measure its output voltage to see if it is consistent with its rated rated voltage, allowing ±10% error. If the generator output voltage is too low, check if the generator winding is open or shorted. If yes, replace or rewind.

2 Check if the rectifier diode breaks through the short circuit. If yes, replace it.

3 Check if the parallel capacitance of the generator is damaged. If yes, replace it.

4 Check if the governor's screw spring is too loose. If so, re-adjust the spring to tighten the spring.

Second, the position of the "∝" and "0" points is normal, but some of the scale points have large errors.

1 mechanical balance is not good. If so, rebalance the balance. The method is: the meter is not energized to rest at a certain position, and then the front and rear, tilted 30 degrees to the left and right to adjust the balance hammer.

2 Re-weld the guide wire, and extend or shorten the guide wire, and use its residual torque to change the scale characteristics of the meter.

3 If the above method does not work, you can redo the tick to solve.

3. When the "E" and "L" are short-circuited, the pointer does not mean "0".

1 If the pointer does not mean "0", you can use the dice to move the pointer to adjust.

2 Check if the current loop resistance increases. If yes, readjust the resistance.

3 Check if the current coil is shorted or open. If yes, rewind or replace.

4 Check if the guide wire is in contact with other objects or deformed greatly. If yes, replace it.

Fourth, the pointer is not smooth or there is a stuck phenomenon when turning

1 Check if the shaft tip is worn. If yes, replace the shaft tip.

2 The jewel bearing is too tightly fitted with the shaft tip, causing the gap to be too small. If so, the clearance between the bearing and the shaft tip should be readjusted.

3 The movable coil of the instrument is deformed to collide with the inner core. If so, rework the wireframe.

4 The guide wire is deformed, causing the pointer to collide with some fixed parts while rotating. If so, readjust the guide wire.

5 The movable coil collides with the iron filings on the magnetic core. If so, a thin steel wire with magnetic properties is inserted into the gap, and the iron scrap is sucked out by the principle that the steel wire is magnetized.

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Label: High-voltage digital megohmmeter use precautions and fault repair methods

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