The megohmmeter consists of a hand-cranked generator, a meter head and three terminals (namely, L: line end, E: grounding end, G: shielding end), "G" (ie shielding end) is also called a protection ring.

Selection of rated voltage level: high-voltage electrical equipment requires high insulation resistance, and a high-voltage megohmmeter must be used for testing; low-voltage electrical equipment internal insulation materials can withstand not high voltage, in order to ensure the safety of the equipment, choose a low-voltage megameter European watch. Generally, 500V or 1000V megohmmeter should be used for equipment with rated voltage below 500V: 1000V-2500V megohmmeter should be used for equipment with rated voltage above 500V.

Selection of resistance range range: The principle of choosing a megohmmeter is not to make the measurement range exceed the value of the measured insulation resistance too much, so as to avoid larger reading errors due to the thicker scale. Also note that the initial scale of some megohmmeters is not zero, but 1MΩ or 2MΩ. This kind of megohmmeter is not suitable for measuring the insulation resistance of low-voltage electrical equipment in a humid environment, because the insulation resistance of the equipment in this environment If it is small, it may be less than 1MΩ, and the reading cannot be read on the meter. It is easy to mistake the insulation resistance as 1MΩ or zero value. There are two small black dots on the dial scale of the megohmmeter, and the area between the small black dots is the accurate measurement area. Therefore, when selecting the meter, the insulation resistance value of the device under test should be within the accurate measurement area.