DC resistance tester measuring high-voltage circuit breaker



A DC resistance tester (also commonly known as a micro-ohmmeter, DC resistance meter, or loop resistance tester) is an essential "physical examination instrument" in the maintenance of power systems and electrical equipment.

Its core function is very clear: it is specifically used for high-precision measurement of low resistance values (typically in milliohms mΩ or microohms μΩ). Since ordinary multimeters have severely insufficient accuracy when measuring extremely low resistances and cannot eliminate the interference of test lead resistance, this professional instrument must be used in power equipment handover and preventive tests.

⚡ Core Working Principle: Four-Wire Method and Ohm's Law

The measurement of a DC resistance tester is based on Ohm's law (R=V/I), but to achieve high precision, it employs the key four-wire (Kelvin) measurement method:

Constant current source output (I+, I-): The instrument outputs a known and extremely stable DC test current (e.g., 1A, 10A, 50A, or even larger) to the object under test.

Precise voltage sampling (V+, V-): While current flows through the object under test, the instrument uses two other independent voltage leads, placed close to both ends of the object, to measure the voltage drop.

Eliminating errors: This physical separation of "current" and "voltage" perfectly eliminates the influence of the test lead resistance and the contact resistance of the wiring clamps on the measurement results, thereby accurately calculating the true DC resistance value of the object under test.