4wire

4wire is a term used in electronics and metrology to describe a four-conductor method for making electrical resistance measurements. In this approach, two conductors supply current to the test object and two separate conductors sense the voltage drop across it. This separation minimizes the influence of lead and contact resistances on the measured value, enabling higher accuracy especially for low resistances or long leads.

Principle: A stable current I is forced through the outer leads, while a high-impedance voltmeter or differential amplifier measures the voltage V across the inner leads directly at the test element. The resistance is calculated as R = V / I. Because the sense path draws negligible current, the resistance of the sense leads contributes negligibly to V, unlike in a 2-wire measurement.

Applications include precision resistance measurements, calibration laboratories, and sensors such as four-wire RTDs or shunts used in metrology. It is also common in calibrated multimeters and data acquisition systems that provide Kelvin sensing options. The technique is sometimes called a Kelvin connection or four-wire sensing.

Variants include 3-wire and 2-wire configurations. A 3-wire arrangement can compensate for the resistance of one lead pair when resistances are similar, while 4-wire measurements fully eliminate lead resistance errors. The choice depends on required accuracy, connection length, and the resistance value being measured.

Notes: The term 4wire can also appear in other contexts, but in metrology it primarily refers to the Kelvin-type four-conductor measurement method. No single governing standard exists for all 4-wire implementations; procedures are defined by instrument manufacturers and metrology guides.