Correct use of multimeter/megohmmeter
1. The megohmmeter must be placed horizontally on a stable and solid place to avoid measurement errors due to jitter and tilt when shaking.
2. The wiring must be correct. The megohmmeter has three wiring posts, "E" (ground), "L" (line) and "G" (protection ring or shielding terminal). The function of the protective ring is to eliminate the influence of leakage between the "L" and "E" terminal posts on the surface of the watch case and the leakage on the surface of the insulator being measured. When measuring the insulation resistance of electrical equipment to ground, "L" uses a single wire to connect to the part of the equipment to be measured, and "E" uses a single wire to connect to the equipment shell; for example, when measuring the insulation resistance between two windings in electrical equipment, connect "L" and "E" are connected to the terminals of the two windings respectively; when measuring the insulation resistance of the cable, in order to eliminate the error caused by surface leakage, "L" is connected to the terminal core, "E" is connected to the shell, and "G" is connected to the terminal core Insulating layer between shells. The connecting wires between "L", "E" and "G" and the object under test must be single wires with good insulation and must not be twisted. The surface must not be in contact with the object under test.
3. The rotation speed of the rocking handle should be uniform, generally 120 rpm, with a variation of ±20% allowed, and a maximum of ±25%. Usually, it needs to be shaken for one minute, and then the pointer can be stabilized before reading. If there is a capacitor in the circuit under test, shake it continuously for a period of time to let the megohmmeter charge the capacitor. After the pointer is stable, take a reading. After the measurement, remove the wiring first and then stop shaking. If the pointer is found to be pointing to zero during measurement, stop shaking the handle immediately.
4. After the measurement is completed, the equipment should be fully discharged, otherwise it may easily cause an electric shock accident.
5. It is prohibited to measure insulation resistance during lightning or on equipment with high-voltage conductors nearby. Measurement can only be done when the equipment is not charged and cannot be charged due to induction from other power sources.
6. Before the megohmmeter stops rotating, do not touch the measuring part of the equipment or the megohmmeter wiring pile with your hands. When removing the wires, do not directly touch the exposed parts of the leads.
7. The megohmmeter should be calibrated regularly. The calibration method is to directly measure a standard resistor with a certain value and check whether the measurement error is within the allowable range.
