Common problems in field test of loop resistance tester:

1. Problems existing in existing test methods

In accordance with the conventional design principles of the circuit resistance tester design in the field test found that there is a common problem: when the tester voltage wiring circuit is bad contact or open circuit, the tester will also show a value, the following situations will occur:

(1) voltage circuit open circuit, no interference of strong electric field test site, in this case, as a result of the amplifier input differential mode voltage basic is zero, so the instrument according to the test values close to zero, if the tester has enough experience of field testing, can judge the instrument is abnormal voltage circuit test line, after test instrument circuit voltage lines exception to rule out, Can get the final correct test results; If the tester does not have enough experience in field testing, it may misjudge the problem of the tester, interrupt the test, replace or repair the instrument, delay the power outage, and bring unnecessary trouble to the test work.

(2) the voltage loop poor contact, most cases of circuit breaker contacts xenophobic surface after terminals in the long run will produce oxide film or film, when the voltage test loop resistance tester clamps when receiving such a terminal on May produce poor contact, both voltage test line clamps itself will produce certain contact resistance, When the contact resistance value is equal to the internal resistance value of the voltage sampling loop, the test results will be seriously affected.

(3) voltage circuit broken or poor contact (when open visual contact resistance R1 infinity), has the strong electromagnetic interference test site, such as busbar electrically charged, the capacitance of electric bus through the medium of air at this time, test the voltage of two lines of interference measurement equipment, due to the effect of interference voltage acquisition circuit tester lines appear on both ends of the differential mode voltage.

If the interference is large, the loop resistance tester will show a much larger value than the resistance value of the test, at this time, if the tester has enough field test experience may be able to determine the abnormal test results, can attract attention and finally get the correct test results. However, if the tester does not have enough experience, he may misjudge that the resistance value of the switch circuit exceeds the standard, and may use the method of outage maintenance to deal with the defect, resulting in unnecessary losses to the power production.

If the intensity of the interference is not very high and the instrument indicates that the value is within the acceptable resistance range of the circuit breaker, this situation is the same as the result of "(2) poor voltage circuit contact" and will also lead to misjudgment.

2. Use the improved four-wire measurement method to solve the above problems.

According to the analysis of the above problems, the four-wire measurement method is improved, and the power supply technology is adopted, which can output large current continuously for a long time, overcome the disadvantage of the instantaneous current of the pulse power supply, and can effectively breakdown the oxide film of the switch contact, and solve the existing problems of the traditional circuit resistance tester.