DC resistance tester (abbreviated as "DC resistance meter") is the "stethoscope" in power equipment testing, 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 whether the winding has broken wires, whether the joint welding is good, whether the tap changer contacts are in place, and whether there are hidden dangers such as inter-turn short circuits.

⚙️ Core Working Principle

The DC resistance tester works based on Ohm's law (R=U/I). To eliminate the influence of test lead resistance and contact resistance, it generally 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.), which is injected 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 the resistance value based on the measured voltage and current values and displays it.

Key technical points:

Four-wire method: The current leads and voltage leads are separated, ensuring that the voltage measurement point is exactly at both ends of the measured resistance, completely eliminating the error of lead resistance.

Demagnetization and discharge: Since the transformer winding is a huge inductive body that stores a large amount of magnetic energy, after the test, the instrument must have automatic discharge and demagnetization functions to protect the safety of operators and prevent residual magnetism from affecting subsequent tests.