Contact Resistance Testers with conventional design principles are found to have a common problem during field testing: when the voltage wiring circuit of the tester has poor contact or open circuit, the tester will display a value, and the following situations will occur with respect to the value:
1. The voltage circuit is open, and there is no strong electric field interference at the test site. In this case, since the differential mode voltage input by the amplifier is basically 0, the test value displayed by the instrument is close to 0. If the tester has sufficient on-site test experience, we can judge that it is the abnormal test line of the instrument voltage circuit. After removing the abnormal test line of the instrument voltage circuit, we can get the final correct test result;
2. The voltage circuit has poor contact. In most cases, the connection terminal of the circuit breaker will produce oxide film or oil film on the external surface of the terminal strip after long-term operation. When the voltage test clamp of the circuit resistance meter is connected to such a terminal strip, poor contact may occur. The voltage test clamp itself also needs to produce a certain contact resistance. When the contact resistance reaches the same value as the internal resistance of the voltage sampling circuit, It will have a serious impact on the test results.
3. The voltage circuit is open or poorly contacted, and there is strong electromagnetic interference at the test site. If the bus is live, the live bus will interfere with the two voltage test lines of the tester through the capacitor with air as the medium, and differential mode voltage will appear at both ends of the voltage acquisition line of the circuit tester due to the interference.