By hvhipot 
A DC Resistance Tester (also called a Micro-ohmmeter or Low-Resistance Ohmmeter) is a precision instrument designed to measure extremely low electrical resistances (typically 0.1 µΩ to 2 kΩ) using direct current (DC). It eliminates inductive/capacitive effects, providing accurate readings for quality control, diagnostics, and maintenance of electrical components.
Key Features & Working Principle
1. 4-Wire Kelvin Measurement (Essential)
Current Leads (C1, C2): Inject a stable DC current (e.g., 1A�C100A).
Voltage Leads (P1, P2): Measure the voltage drop directly across the test object, bypassing lead/contact resistance.
Accuracy: ±0.1% or better, critical for sub-ohm measurements.
2. High Test Current
Uses DC currents (1A�C1000A) to overcome thermal EMF/noise and improve signal-to-noise ratio.
Example: Measuring a 500 µΩ busbar requires ≥10A to detect 5 µV changes.
3. Automatic Stabilization & Averaging
Compensates for inductive “ramp-up” in windings (transformers/motors).
Averages multiple readings to cancel noise.
Primary Applications
Transformers: Measure winding resistance per phase (detects loose connections, broken strands).
Motors/Generators: Test armature/field windings (identify shorts, opens, imbalances).
Switchgear: Check contact resistance in breakers, busbars, joints (target: <50 µΩ for HV contacts).
Cables/Busbars: Validate bonding resistance and joint integrity.
Welding/Manufacturing: Quality control of electrical joints.