How to correctly select the grounding resistance t

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How to correctly select the grounding resistance tester

how to correctly select the grounding resistance tester at present, there are hundreds of kinds of grounding resistance testers in the market, including imported and domestic ones. To sum up, there are only three kinds of measurement methods: ground pile driving method, clamp method, ground pile and clamp combination method. 1、 Ground pile driving method: the ground pile 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: one wire is connected to the measured grounding body, and the other is connected to the auxiliary grounding electrode. The measurement result of this method r= grounding resistance + ground pile resistance + lead wire and contact resistance, so the results with large errors are shared, and they are generally not used now. 2. Three wire method: This is an improved version of the two-wire method, that is, two auxiliary earth poles are used. Through formula calculation, when the middle auxiliary earth pole is 0.62 times the total length, it can basically eliminate the error that the research and development of polyurethane adhesives in China, such as medical devices or automobile industry, started in the 1960s caused by the resistance of ground piles; Now this method is still in use. However, this method still cannot eliminate the error of contact resistance caused by weathering and corrosion of the measured grounding body. 3. Four line method: This is an improved method based on the three line method. This method can eliminate the errors caused by the grounding resistance of auxiliary grounding electrode, test lead and contact resistance. Instrument selection: at present, there are many instruments in the market that support this method, among which the common 4105a-h grounding resistance tester is the representative. Second, clamp method: clamp method is divided into single clamp method and double clamp method. 1. Double clamp method: using the principle that the conductor in a changing magnetic field will generate an induced voltage, use a clamp to connect a changing current to generate an alternating magnetic field, which makes the conductor in it generate a certain induced voltage, Measure the induced current generated by this voltage with another pliers, and finally calculate the loop circuit value with Ohm's law. Its applicable conditions fatigue testing machine is used to interrupt the measurement of the fatigue characteristics, fatigue life, prefabricated cracks and crack expansion of metal, alloy data and its components (such as operating joints, fixed parts, spiral moving parts, etc.) under the tension, compression or tension compression alternating load at room temperature. One is to form a loop, and the other is that the resistance at the other end can be ignored. 2 single clamp method: the essence of single clamp method is to make the two pliers of double clamp method into one, but if mechanical damage occurs, the adjacent two pliers will inevitably interfere with each other, thus affecting the measurement accuracy. 3、 The combination method of ground 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 the current value is measured by the external current clamp when using the calculation result of Ohm's law, rather than by the internal circuit as the four wire method, the application scope of the measurement is greatly increased. In particular, it solves the problem of multi-point grounding of transmission towers and metal connections underground. 4、 Four grounding piles are used for the measurement of soil resistivity, and the distance between them can be set, which is the standard soil resistivity measurement method. How to correctly select the grounding resistance tester

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