The ground resistance tester (also called ground resistance measuring instrument) should be used when testing the ground resistance. In use, not only the method steps used, but also the correct and appropriate instrument should be selected. There are only three types of measurement methods: ground pile method , Clamp method, ground pile and clamp combination method, the following is an introduction to these three types of methods for correct selection of grounding resistance testers.

Ground pile method:

The ground stake method can be divided into two-wire method, three-wire method and four-wire method. 1, two-wire method: This is the initial measurement method: connect one wire to the grounding body under test and the other to the auxiliary ground pole. The measurement result of R=ground resistance + ground pile resistance + lead and contact resistance, so the error is relatively large, it is generally not used now, 2. Three-wire method: This is an improved version of the two-wire method, that is, using two auxiliary ground electrodes, through the formula Calculated, when the middle auxiliary ground pole is 0.62 times the total length, the error caused by the resistance of the ground pile can be basically eliminated. This method is still in use, but this method still cannot eliminate the weathering and corrosion caused by the measured grounding body. Contact resistance error, 3. Four-wire method: This is an improved method based on the three-wire method. This method can eliminate errors caused by auxiliary grounding resistance, test leads and contact resistance.

Clamping method:

The clamp method is divided into single clamp method and double clamp method. 1. Double clamp method: using the principle that a conductor in a changing magnetic field generates an induced voltage, a pliers is used to pass a changing current to produce an alternating magnetic field. The magnetic field causes the conductor inside to generate a certain induced voltage. Use another pliers to measure the induced current generated by this voltage. Finally, use Ohm's law to calculate the loop circuit value. The applicable conditions are to form a loop and the other is the resistance at the other end. It can be ignored. 2. Single clamp method: The essence of the single clamp method is to make the two pliers of the double clamp method into one body, but if mechanical damage occurs, the two adjacent pliers will inevitably interfere with each other, which will affect the measurement accuracy.

Combination method of pile and clamp:

This method is also called the selective electrode method. The measurement principle of this method is the same as that of the four-wire method, because when the results are calculated by Ohm’s law, the current value is measured by an external current clamp instead of the internal one like the four-wire method. The circuit is measured, thus increasing the scope of measurement, especially solving the problem of multi-point grounding of power transmission towers and metal connections underground.