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Question about contact resistance tester used on field

time:2022-08-30

When the contact resistance tester designed according to traditional design principle is working in field, there is a common problem. When the voltage circuit of device is disconnected or short- circuit, the device will display a value and the following will happen;

1. The voltage loop is open, and there is no strong electric field interference in the test site. In this case, because the differential mode voltage of the amplifier input is basically 0, so the device displays the test value close to 0. If the user has enough experience of field test, he can judge the instrument voltage test line abnormal circuit abnormal and return the instrument voltage. After eliminating abnormal test paths, the final correct test results can be obtained.

2. Voltage circuit is in poor contact. In most cases, the terminal of the circuit breaker will produce an oxide film or oil film on the outer surface of the terminal after long-term operation. When the voltage test clamp of a circuit resistor is clamped on such a terminal board, may have poor contact. When the voltage test clamp itself also produces a certain contact resistance, the contact resistance value is the same as the internal resistance value of the voltage sampling circuit. It will have a serious impact on the test results.

3. The voltage circuit is open or has poor contact (contact resistance value r1 is infinitely great when open), there is strong electromagnetic interference at the test site, such as a live bus. At the point, the charged bus passes through the capacitor with air as the medium, interferes with two voltage test lines of the tester. Due to interference, the voltage acquisition line of the loop resistance tester is two. The differential mode voltage appears at the end.