The grounding resistance meter is used to measure the grounding resistance of grounding devices, such as protective grounding, working grounding, anti-overvoltage grounding, anti-static grounding, and lightning protection grounding, that is, the resistance of the grounding device when the power frequency current flows, including the grounding wire Resistance, grounding body resistance, contact resistance between grounding body and the earth, and ground stray resistance.

There are mechanical and digital grounding resistance meters or two types.

Ordinary grounding resistance meters look like insulation resistance meters, and there are many models and sizes. With the development of electronic technology, new ground resistance meters have sprung up. The working principle of ground resistance measuring instrument is divided into reference voltage comparison type, reference current type and voltage drop type. The grounding resistance measuring instrument borrows the principle of the electric bridge to compare the measured resistance with the known resistance through a proportional device. After adjusting the balance, directly read the measured grounding resistance value through the scale on the known resistance. The grounding resistance meter usually has two auxiliary electrodes: one is used to inject current, called current pole c; the other is used to sample voltage, called voltage pole p. If the load of the current source is strong, the ground resistance of the current electrode c does not affect the measurement result; if the impedance of the sampling voltage terminal is strong, the ground resistance of the P electrode does not affect the measurement result.

The grounding resistance meter should use AC power. This is because the electrical conductivity of the soil mainly depends on the role of the electrolyte in the soil, and direct current measurement will produce polarization electromotive force, resulting in large measurement errors. However, since the ammeter used as the zero indicator is of the magnetoelectric system, the meter is equipped with a mechanical rectifier (or phase-sensitive rectifier) to rectify the alternating current into direct current and send it to the galvanometer.