Four-Wire Kelvin Measurement

Circuit Configuration

The method uses separate pairs of wires for the current supply and the voltage measurement across the test resistor. One pair, known as the force leads, delivers a known current through the component from a stable current source. The second pair, called the sense leads, connects directly to the resistor terminals to measure the voltage drop with a high-impedance voltmeter.

Because almost no current flows through the sense leads, there is no significant voltage drop across them, which allows the meter to capture the exact voltage across the resistor.

Contact Resistance

Traditional two-wire measurements include the resistance of the test leads and the contact interfaces in the total measurement. In low-resistance scenarios, these parasitic resistances can be much larger than the resistance being measured, leading to massive errors. By separating current and voltage paths, this technique bypasses these contact errors entirely, making it indispensable for sub-ohm measurements.

Industrial Execution

In automated manufacturing lines, specialized spring-loaded test probes called Kelvin pins contact the device terminals to execute these tests rapidly. These systems are used to verify the quality of solder joints, busbars, and power semiconductor packages. Implementing this technique ensures that minor defects like microscopic solder cracks or material impurities are detected before assembly.

This protocol maintains the safety and reliability of high-current power electronics.