1. The voltage wiring circuit is open or poorly connected (the contact resistance is infinite when the wiring is disconnected). When there is strong electromagnetic interference around the test, such as the bus bar is charged, at this time, the charged bus bar will pass through with air as the medium, which will cause interference to the capacitance of the tester. Due to interference, the differential mode voltage of the two voltage test lines appears at both ends of the voltage acquisition line of the loop tester.
If the external interference is great, the loop resistance tester will display a value much larger than the resistance value of the tested product. At this time, if the tester has satisfactory field test experience, he can judge the abnormality of the test result and deal with it, so as to attract people's attention and finally get the correct test result. However, if the tester is inexperienced, he can get the correct test result, may misjudge the resistance value of the switching circuit, and may use power failure to deal with shortcomings, which will cause unnecessary power loss in the future; if the interference intensity is not large , The value displayed by the meter is only within the qualified resistance range of the circuit breaker. This situation is the same as the result of "poor contact in the voltage circuit" and may also lead to misjudgment.
2. The voltage wiring circuit is disconnected, the loop resistance tester is turned on, and there is no strong electric field interference at the test site. In this case, because the amplifier basically has no differential mode voltage input, the test parameter displayed by the tester is close to 0; if the tester has satisfactory field test experience, it can be confirmed that the voltage loop test line of the instrument is abnormal. After removing the abnormal voltage loop test line of the instrument, the final correct test result can be obtained; otherwise, you may mistakenly think that there is a problem with the tester and interrupt the test. Replacing or refurbishing the tester will delay the power-off time and bring unnecessary trouble to the test operation.
3. Poor connection of the voltage circuit wiring. In most cases, after a long-term operation of the circuit breaker terminal, an oxide film or oil film will be formed on the surface of the terminal block, resulting in poor contact. The voltage contact resistance test clip itself will seriously affect the test result.