Talking about the common problems of field resistance tester field test

Most of the loop resistance testers on the market use a typical four-wire measurement method. The high-frequency switching power supply provides a test current greater than 100A. When the measurement button is pressed, the high-frequency switching power supply outputs a test current greater than 100A. The sampling circuit starts sampling, and the obtained signal is amplified by the amplifier, and the analog signal is converted into a digital signal by the A/D converter, and then the data is filtered, calculated, processed by the microprocessor, and finally sent to the display to display the measurement. Current and resistance values. And when the current test circuit is broken or the contact is bad, the instrument will judge the current circuit to contact poorly or open circuit according to the voltage on the current shunt. The DC resistance fast tester adopts new power supply technology and features fast measurement, small size, convenient use and high measurement accuracy. It is an ideal device for measuring transformer windings and DC resistance of high-power inductors.

Problems with existing test methods

The loop resistance tester designed according to the conventional design principle found that there is a common problem in the field test: when the tester voltage wiring circuit has poor contact or open circuit, the tester will also display a value, and the following will appear. Happening:

(1) The voltage loop 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 field test experience, It can be judged that the instrument voltage loop test line is abnormal. After the instrument voltage loop test line is abnormally excluded, the final correct test result can be obtained. If the tester does not have enough field test experience, the tester may be misjudged and interrupted. Test, replace or rework the instrument, delay the power outage time, and bring unnecessary trouble to the test work. (2) Poor contact of the voltage circuit. In most cases, the terminal of the circuit breaker will produce an oxide film or oil film on the outer surface of the terminal block after long-term operation. When the voltage tester of the loop resistance meter is clamped to such a terminal block, it may be Poor contact occurs, and the voltage test line clamp itself also generates a certain contact resistance. When the contact resistance value is equal to the internal resistance value of the voltage sampling loop, the test result will be seriously affected. (3) The voltage circuit is open or poorly contacted (visible contact resistance R1 is infinite when the circuit is open), and there is strong electromagnetic interference at the test site. For example, if the bus is charged, the live bus will pass through the air-based capacitor and interfere with the tester. The strip voltage test line causes the differential mode voltage to appear at both ends of the voltage test line of the loop tester due to the interference. If the interference is large, the loop resistance tester will display a value much larger than the resistance value of the test object. At this time, if the tester has sufficient field test experience, it may be able to judge the abnormality of the test result, which can attract attention and eventually Get the correct test results. However, if the tester does not have enough experience, the switch circuit resistance value may be misjudged, and the power failure maintenance method may be used to deal with the defect, causing unnecessary loss to the power production.

If the intensity of the disturbance is not very large, the instrument display value is within the acceptable resistance range of the circuit breaker. This situation is the same as the result of the situation "(2) Poor contact of the voltage loop", which will also cause misjudgment.

2. Solve the above problems with the improved four-wire measurement method.

According to the analysis of the above problems, the proposed four-wire measurement method is adopted. The latest power supply technology can continuously output large current for a long time, which overcomes the shortcomings of the instantaneous current of the pulsed power supply, and can effectively break through the oxide film of the switch contact. The current problems with conventional loop resistance testers. The test sample is powered by a large current constant current source, and the voltage and current values ​​are collected to calculate the resistance value of the sample. The value measured at this time must be the actual resistance value of the sample, and the generation of false data is eliminated. Even if there is strong electric field interference in the field, because the resistance in the voltage loop is very small, the voltage at the voltage test terminal is the common mode voltage. This product reduces the AC common mode interference to a very low level by means of capacitor grounding. Accuracy has an impact. The above indicates that the automatic judgment and prompt function greatly improves the test accuracy and improves the production efficiency, and is a reliable basis for the field tester to quickly solve the problem.