DC resistance tester is often referred to as direct resistance meter or micro-ohmmeter
It is a key instrument used in the power industry, electrical manufacturing, and laboratories for accurately measuring the DC resistance of inductive loads (such as transformer windings, motor coils, instrument transformers, etc.). It is mainly used to replace traditional DC single-arm/double-arm bridges, featuring fast testing speed, high accuracy, and high automation. The following is a summary of core information about this instrument: 1. Main Uses Transformer Testing: Check winding welding quality, presence of inter-turn short circuits, tap changer contact condition, and whether lead connections are loose or have missing strands or broken wires. Motor and Instrument Transformer Testing: Measure the DC resistance of stator/rotor windings and instrument transformer coils to determine coil integrity. Application Scenarios: Factory tests, installation acceptance tests, post-overhaul tests, and preventive tests by power departments. 2. Working Principle Constant Current Source Method: The instrument internally generates a stable large DC current (e.g., 1A, 5A, 10A, 20A, or even higher) and injects it into the winding under test. Four-Wire Measurement (Kelvin Method): Uses two current leads (I+, I-) and two voltage leads (V+, V-). The current leads provide the test current, while the voltage leads specifically collect the voltage drop across the test object. This design completely eliminates the influence of test lead resistance and contact resistance on measurement results, ensuring accuracy for micro-ohm (mΩ/μΩ) measurements. Ohm's Law Calculation: Based on
