WRR-621 WRR-620 WRR-622 B type thermocouples, the ground resistance meter is a commonly used measuring instrument. It is widely used in the measurement of ground resistance of electrical equipment and transmission lines in the fields of electricity, lightning protection, communication, transportation and other fields. It is an indispensable tool for electrical safety inspection and completion acceptance of ground engineering. . With the continuous development of science, the measurement method of grounding resistance is also continuously improving. The development of grounding resistance meters to the current stage mainly has the following three types: ① analog grounding resistance meters, which are more traditional meters, and the basic principle is The three-point voltage drop method is used. The measurement method is to insert two auxiliary test poles on the same side of the ground to be measured. The three are on the same line. The distance between the auxiliary test pole and the ground to be measured is about 20m and 40m, respectively. Rotate the crank at a certain speed, so that the motor inside the resistance meter generates electrical energy, generates a current between the electrodes at both ends, and forms a loop, thereby generating a voltage between the measured electrode and the auxiliary electrode, thereby calculating the measured ground electrode. The resistance. Its disadvantage is that it is hand-cranked, and the output voltage is not stable enough, which affects the measurement results. ② Digital ground resistance tester, its measurement methods are two-wire method, three-wire method, four-wire method. The wiring method of the three-wire method is the same as the analog ground resistance meter, but its stability is much better than the former. The two-wire method does not require auxiliary grounding piles, and can use water pipes, neutral wires of AC outlets, etc. as auxiliary grounding. The four-wire method is improved on the basis of the three-wire method. In the case that low-value measurement and wiring have a large impact on the measurement result, it can effectively eliminate errors and improve accuracy. ③ Clamp ground resistance tester, its measurement methods include single clamp method and double clamp method, based on the two-pole method. The jaw part of the clamp meter includes voltage and current coils. The voltage coils provide excitation signals and induce a potential E on the circuit under test to generate the loop current I. Measure E and I to get R, which is simply a full circuit The embodiment of Ohm's law in practice. It is a novel measurement tool that is convenient and fast. It does not require auxiliary test poles. You only need to pinch the geodesic line to get the result. In addition, it also has the advantage that the resistance of the device can be measured online, unlike traditional meters, which cut off the power or disconnect the ground wire. However, it still has large limitations. Its measured value is actually the entire loop resistance including the tested ground resistance, and it is susceptible to interference from external electromagnetic fields. It cannot measure the resistivity of soil and cannot completely replace the traditional ground. The resistance meter measures the ground resistance of a single grounding body.
It can be seen that the testing technology of grounding resistance has developed to the current stage. Clamp-type grounding resistance meters and traditional grounding resistance meters have their own advantages and disadvantages. In the actual measurement process, users must choose the best instrument according to the actual situation. There is still much room for development of ground resistance measurement methods.