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 loop has poor contact or open circuit, the tester will also display a value, and the following will appear at this time Condition:

1. The loop resistance test is connected to the 220V AC power supply, the fan is silent, and the "test switch" is pressed, the ammeter and micro-ohm meter have no display.

2. To test the loop resistance, press the "test switch", the ammeter will display no current, and the micro-ohm meter will display "1".

3. Loop resistance test The test current is normal, and the micro-ohm value bit displays "1"

In view of the above problems, we can use the improved four-wire measurement method to solve.

Based on the analysis of the above problems, an improved four-wire measurement method is proposed. Using power supply technology, it can continuously output large currents for a long time, overcome the shortcomings of pulsed power supply transient currents, and can effectively break down the switch contact oxide film, and solve the current problem. Problems with traditional loop resistance testers.

The test sample is energized by a high-current constant current source, the voltage and current values are collected, and the resistance value of the sample is calculated. The value measured at this time must be the real resistance value of the test product, which prevents the generation of false data. Even if there is strong electric field interference on site, because the resistance in the voltage loop is very small, the voltage induced to the voltage test terminal is a common mode voltage. This product uses capacitor grounding to reduce this AC common mode interference to a very low level and will not affect the test. Accuracy has an impact.