Loop resistance tester is a special instrument used for the measurement of contact resistance and loop resistance of switch control equipment, and its principle is mainly based on Ohm's law.
During the measurement, the loop resistance tester will output a current of 100A or more from a high-frequency switching power supply, apply it between the two end buttons of the resistor to be measured, collect the voltage drop analog signal generated by the current flowing through the measured resistor through the sampling circuit, and then amplify it through the preamplifier, and then convert the analog signal into a digital signal by the A/D converter. In addition, the loop resistance tester adopts a high-reliability high-power integrated circuit, which is composed of a DC constant current source, a preamplifier, an A/D converter, an indication device and other parts.
When using the loop resistance tester, the test clips of the loop resistance tester should first be clamped at both ends of the device under test to ensure that the clips are in good contact and the electrodes are close to the surface to be measured. Then press the test button, observe the tester's display, wait for a period of time (usually 10 seconds) and read the displayed resistance value. If the test result shows that it is too large or too small, you can adjust the test current level to re-measure. At the same time, according to the four-wire measurement method, connect the test product to the instrument panel with a special test line, pay attention to the voltage measurement line should be connected to the inside of the current output line, turn on the AC220V power supply (note: the third line of the power supply incoming line, that is, the protective ground, must be connected to the ground), press the power switch, and the ammeter and resistance meter will be displayed at this time.