FOUR-WIRE KELVIN CONNECTIONS
Making low-resistance measurements, under 1Ω, is subject to sources of error including lead resistance and contact resistance. This tech note describes these problems and how they are overcome.
To measure the resistance of a component, a test current is forced through the component via a set of test leads. The meter then measures the voltage across its terminals to give the component's resistance value. This is known as a two-wire measurement. In a two-wire measurement, the value of resistance is subject to the resistance of the test leads. The lead resistance causes a small volt drop, which can usually be considered negligible.
The problem with the two-wire method is that, when measuring small values of resistance, typically 1Ω or less, the resistance of the test leads causes a relatively significant volt drop in addition to the volt drop across the component (Figure 1). The voltage measured by the meter will therefore not be the true value of the voltage across the component.