Brief introduction of the measuring principle of t

2022-09-19
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Introduction to the measurement principle of the clamp type ground resistance tester

I. The measurement principle of the clamp type ground resistance tester the clamp type ground resistance tester is a novel measurement tool. It is convenient and fast, and its shape is similar to the clamp type ammeter. During the test, there is no need for auxiliary test piles, just a clamp on the measured ground wire, and the measurement results can be obtained in a few seconds, which greatly facilitates the ground resistance measurement work. The clamp type ground resistance meter also has a great advantage that the hydraulic system works normally. It can measure the ground resistance of the equipment in use without cutting off the power supply of the equipment or disconnecting the ground wire. The ring next to e and I in the circuit indicates that the pliers readjust the ring bayonet of the oscilloscope range shaped ground resistance meter again, Rx is the ground resistance of the geodesic pile, R1, R2 RN is the ground resistance of other grounding points in the distributed grounding system. This figure can be further equivalent to figure 3. During measurement, the clamp type ground resistance meter uses the principle of electromagnetic induction to send a constant voltage e to the measured cable through the loop formed by its front-end bayonet (with electromagnetic coil inside), which is applied to the circuit shown in Figure 3. The ground resistance meter can simultaneously measure the current I in the circuit through its front-end bayonet. According to e and I, the total resistance in the circuit can be calculated, That is, E/I = RX + 1/(1/R1 + 1/r2 +... + 1/RN) experimental methods of various materials are also described in terms of strength experiments. 1/(1/R1 + 1/r2 +... + 1/RN) is R1, R2 The total resistance of RN after parallel connection in the distributed multipoint grounding system usually has RX>> 1/(1/R1 + 1/r2 +... + 1/RN), ">>" means "much greater than". Assuming the above conditions are true, the measured ground resistance RX = E/I

in fact, the 1.7khz AC constant voltage is fed into the cable through the special electromagnetic converter of its front snap ring. In the current detection circuit, after filtering, amplification and a/D conversion, only the current generated by the 1.7khz voltage is detected. Because of this, the clamp type ground resistance meter eliminates the small current on the ground wire caused by the commercial AC and the high-frequency noise generated by the equipment itself, so as to obtain accurate measurement results. Because of this, the clamp type ground resistance meter has the advantage of measurement. In fact, the meter measures the impedance of the whole circuit, not the resistance, but under normal circumstances, the difference between them is very small. The clamp type ground resistance meter can immediately display the results on the LCD screen. When the bayonet is not clamped properly, it can display "open jaw" or similar symbols on the LCD. Due to the special structure of the clamp type ground resistance meter, it can be easily used as an ammeter. Many of these instruments have the function of clamp type ammeter at the same time. On the other hand, although a certain frequency signal is used to eliminate interference during the test of the clamp type ground resistance meter, the measurement will also be disturbed when there is a large current on the tested cable, resulting in inaccurate results. Therefore, according to the requirements, the current on the cable should be measured before use, and the ground resistance can be further measured only when the current is not very large. Some instruments automatically detect the noise interference when measuring the ground resistance, and will give a prompt when the interference is too large to measure. 2、 From the above introduction, it can be seen that the measurement principle of the clamp type ground resistance meter is completely different from that of the hand-operated ground resistance meter. When using the hand-operated earth resistance meter, the grounding pile should be disconnected from the equipment to avoid the influence of the grounding body of the equipment on the accuracy of measurement. The hand-operated earth resistance meter can obtain high accuracy, regardless of the single point grounding and multi-point grounding system; The most ideal application of the clamp type ground resistance meter is to be used in the distributed multi-point grounding system. At this time, the grounding piles used in the grounding system should be measured in turn, and the measurement results should be recorded, and then compared. For the grounding piles whose measurement results are significantly larger than those of other points, it is necessary to focus on the inspection. If necessary, disconnect the grounding pile from the equipment and retest with the hand-operated ground resistance meter to expose the bad grounding piles. In the single point grounding system, we should be careful to use the clamp type ground resistance meter. From its working principle, we can see that only by mastering the correct method: the resistance value measured by the clamp type ground resistance meter is the total resistance in the circuit. Only when RX>> 1/(1/R1 + 1/r2 +... + 1/RN), the resistance value is similar to the ground resistance of the grounding pile we want to measure, and this condition is not satisfied in many cases, especially in the single point grounding system. For the open circuit grounding pile that has been buried but has not been connected with the equipment, its ground resistance cannot be measured by this instrument at all

it is suitable for grounding leads of various shapes. The non-contact grounding resistance is fast and safe, with double protective insulation, strong anti-interference, self-test function and high measurement accuracy

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