High voltage megohmmeter is an intelligent insulation resistance testing instrument. The overall circuit design adopts microcomputer technology as the core, combining large-scale integrated circuits and digital circuits, equipped with powerful measurement and processing software, to complete the measurement of insulation resistance, voltage, low resistance and other parameters. It has stable performance and easy operation. It has a series of major functions such as automatic range recognition, automatic data storage quantity, automatic shutdown, polarization index, absorption ratio, measurement data comparison, battery display, background light, bar graphic display, USB computer connection function, over range alarm and high voltage warning indication, etc. It is an ideal choice for power departments and construction units.

There are three terminals for a high-voltage megohmmeter: one is the "L" terminal, one is the ground terminal, and the other is the shielding terminal (also known as the protective ring). Generally, the measured insulation resistance is connected between the "L" and "E" terminals. However, when the surface leakage of the measured insulator is severe, the shielding ring or the part that does not need to be measured must be connected to the "G" terminal. In this way, the leakage current flows directly back to the negative terminal of the generator through the shielding terminal "G" to form a circuit, without passing through the measuring mechanism (moving coil) of the megohmmeter. This fundamentally eliminates the influence of surface leakage current. It is particularly important to note that when measuring the insulation resistance between the cable core and the outer surface, the shielding terminal "G" must be connected properly, because when the air humidity is high or the insulation surface of the cable is not clean, the surface leakage current will be large. To prevent the influence of the measured object on its internal insulation measurement due to leakage, a metal shielding ring is generally added to the outer surface of the cable and connected to the "G" terminal of the megohmmeter.

When using a megohmmeter to measure the insulation resistance of electrical equipment, it is important to note that the "L" and "E" terminals cannot be connected in reverse. The correct connection method is to connect the "L" terminal to the conductor of the tested equipment, the "E" ground terminal to the equipment casing, and the "G" shield terminal to the insulation part of the tested equipment. If "L" and "E" are connected in reverse, the leakage current flowing through the insulation body and surface will be collected by the outer shell to the ground, and then flow into the measuring coil through "L" from the ground, causing "G" to lose its shielding effect and causing significant measurement errors. In addition, because the insulation degree between the internal leads of the "E" end and the shell is lower than that between the "L" end and the shell, when the megohmmeter is used on the ground and the correct wiring method is used, the insulation resistance between the "E" end and the instrument shell and the shell to ground is equivalent to a short circuit and will not cause errors. However, when the "L" and "E" are connected in reverse, the insulation resistance between the "E" end and the ground is parallel to the measured insulation resistance, resulting in a smaller measurement result and a larger measurement error.