Loop resistance tester is specifically used for high-precision measurement of high-voltage switchgear



Loop resistance tester (also commonly known as contact resistance tester, micro-ohmmeter) is an indispensable "stethoscope" in the detection of high-voltage switchgear equipment in power systems.

Its core function is very clear: it is specifically used for high-precision measurement of the conductive loop resistance of high-voltage switchgear, circuit breakers, disconnectors, and other equipment. Since the contact resistance of these devices is usually at the micro-ohm (μΩ) level, ordinary multimeters cannot measure it accurately, so a professional instrument capable of outputting large currents must be used.

⚡ Core working principle: DC voltage drop method and four-wire system

The measurement of the loop resistance tester is based on Ohm's law (R=U/I), but to break through oxide films and eliminate interference, it adopts two core technologies:

High-current constant current source: The instrument can output a DC constant current of 100A, 200A, or even larger as specified by national standards. Such a large current can effectively break through the oxide film and oil film on the surface of switch contacts, thereby measuring the true contact resistance value.

Four-wire (Kelvin) measurement method: The instrument is equipped with two thick current wires (I+, I-) and two thin voltage wires (V+, V-). The current wires are responsible for delivering large current, while the voltage wires are placed close to the measured point to collect the voltage drop. This physical separation design perfectly eliminates the interference of the test lead's own resistance and the contact resistance of the wiring clips on the measurement results, ensuring extremely high precision at the micro-ohm level.