DC resistance tester (abbreviated as "direct resistance meter") is the stethoscope in power equipment testing



It is mainly used to measure the DC resistance of inductive load windings such as transformers, motors, and instrument transformers.

Its core function is to diagnose whether the "blood vessels" of electrical equipment are unobstructed by measuring tiny resistance values—that is, to check for broken windings, poor solder joints, improper contact of tap changers, and hidden dangers such as inter-turn short circuits.

⚙️ Core Working Principle

The DC resistance tester operates based on Ohm's law (R=U/I). To eliminate the influence of test lead resistance and contact resistance, it commonly adopts the four-terminal measurement method (also known as the four-wire method or Kelvin method).

Constant current source output: The instrument internally generates a stable DC current (such as 1A, 5A, 10A, etc.) and injects it into the winding under test through a pair of current terminals (C1, C2).

Voltage sampling: While the current is stable, the voltage drop across the winding is precisely collected through another pair of independent voltage terminals (P1, P2).

Calculation and display: The instrument automatically calculates and displays the resistance value based on the measured voltage and current values.

Key technical points:

Four-wire method: The current and voltage lines are separated, ensuring that the voltage measurement points are exactly at both ends of the resistance under test, completely eliminating errors from lead resistance.

Demagnetization and discharge: Since transformer windings are large inductive bodies storing significant magnetic energy, after testing, the instrument must have automatic discharge and demagnetization functions to protect operator safety and prevent residual magnetism from affecting subsequent tests.