Five Principles for Multimeter Selection
(1) Selection of rated voltage level. In general, equipment with a rated voltage below 500V should use a 500V or 1000V megger; For equipment with a rated voltage above 500V, use a shaking meter with a voltage range of 1000V~2500V.
(2) Selection of resistance range. There are two small black dots on the scale line of the dial of the shaking table, and the area between the small black dots is the accurate measurement area. So when selecting a table, the insulation resistance value of the tested equipment should be within the accurate measurement area.
2. Use of a shaking table
(1) School schedule. Before measurement, the shaking table should undergo an open circuit and short circuit test to check if it is in good condition. Open the two connecting wires, shake the handle, and the pointer should point to "∞". Then short-circuit the two connecting wires again, and the pointer should point to "0". If the above conditions are met, it is considered good. Otherwise, it cannot be used.
(2) The tested equipment is disconnected from the circuit, and for large capacitor equipment, discharge is required.
(3) Select a shaking meter that meets the voltage level requirements.
(4) When measuring insulation resistance, generally only the "L" and "E" terminals are used. However, when measuring the insulation resistance of cables to ground or when the leakage current of the tested equipment is severe, the "G" terminal should be used and connected to the shielding layer or shell. After the circuit is connected, the handle can be rotated clockwise. The shaking speed should be slow and fast. When the speed reaches about 120 revolutions per minute (ZC-25 type), maintain a constant speed and read after 1 minute. The reading should be taken while shaking and cannot be stopped.
(5) Unplug and discharge. After reading, shake slowly while disconnecting the wire, and then discharge the device under test. The discharge method is to remove the ground wire used for measurement from the shaking table and short-circuit it with the tested equipment (not discharge the shaking table).
