Meaning
Resistance testing setups in high-precision electronic instruments isolate the voltage drop across a load from the resistance of the test leads. This wiring topology, known as a four-wire Kelvin connection, utilizes separate pairs of test leads for current delivery and voltage measurement. It eliminates lead resistance and contact resistance from the measured value.
Measuring Circuit
Two high-impedance sense terminals measure the voltage across the device under test while two source terminals supply the current. Employing a four-wire Kelvin connection ensures that the current flows almost exclusively through the source loop. This path prevents the voltage sense leads from carrying current and causing parasitic voltage drops, which would otherwise introduce significant measurement noise and skew the resistance readings in low-impedance battery cells.
Error Reduction
Contact resistance at the probe tips can vary during automated cell testing. Implementing a four-wire Kelvin connection resolves this variability by measuring voltage directly at the cell terminals. This configuration improves the repeatability of internal resistance measurements down to fractions of a milliohm.
Equipment Integration
Cell sorting machines rely on precise internal resistance values to match cells for pack assembly. Integrating a four-wire Kelvin connection into the test fixture is necessary to achieve the measurement accuracy needed for high-quality sorting. This prevents the misclassification of acceptable units.
