Four-terminal sensing, or 4-wire sensing is an electrical impedance measurement technique that uses separate pairs of current-carrying and voltage-sensing electrodes to make more accurate measurements than the simpler and more usual two-terminal sensing. Four-terminal sensing is used in some ohmmeters and impedance analyzers, and in wiring for strain gauges and resistance thermometers.
Separation of current and voltage electrodes eliminates the lead and contact resistance from the measurement. This is an advantage for precise measurement of low resistance values.
Four-terminal sensing is also known as Kelvin sensing, after William Thomson, Lord Kelvin, who invented it in 1861 to measure very low resistances with the help of a four-terminal sensing. Moreover, each two-wire connection can be called a Kelvin connection. A pair of contacts that is designed to connect a force-and-sense pair to a single terminal or lead simultaneously is called a Kelvin contact. A clip, often a crocodile clip, that connects a force-and-sense pair is called a Kelvin clip.