Fourterminal

Four-terminal operation, commonly called Kelvin four-wire measurement, is a technique used to measure the resistance of a component with high accuracy by separating current-carrying leads from voltage-sensing leads. In this arrangement two leads supply current through the device, while a separate pair of leads measures the voltage drop across the device. Because the voltmeter draws negligible current, resistance is determined from V/I with the lead and contact resistances of the current path not contributing to the measurement. This minimizes systematic error especially for low-value resistors, shunts, or materials with small resistances.

Implementation and devices: Four-terminal measurements are standard in metrology and are implemented in precision ohmmeters, impedance analyzers, and resistance-temperature detectors (RTDs). In RTD sensors, a four-wire (sometimes three-wire) configuration is used to cancel lead resistance. In practice, a four-terminal resistor may have four pads or four blade terminals; some instruments allow four-terminal sense using Kelvin clamps.

Advantages and limitations: The method improves accuracy and reduces sensitivity to lead resistance and contact resistance, but requires extra leads, connectors, and measurement electronics. At high frequencies, parasitic inductance and capacitance can reintroduce errors, and long leads can add noise.

See also: Kelvin connection, RTD, Wheatstone bridge.