Four Wire Sensing

Circuit Operation

In a standard two-wire measurement, the current flows through the same leads used to measure the voltage, meaning the measured value includes the resistance of the leads and the contact interfaces. In contrast, this advanced configuration uses two outer leads to force a known current through the device under test, while two inner leads measure the voltage drop. Because the voltage measurement circuit has an extremely high input impedance, almost no current flows through the sensing leads, rendering their resistance irrelevant to the measurement accuracy.

Hardware Implementation

Implementing this technique requires specialized connectors, such as Kelvin clips or dual-point coaxial probes, that keep the two circuits isolated until they touch the cell terminal. These probes must be designed to withstand high repetition rates in automated production environments. The physical spacing between the current injection point and the voltage sensing point on the terminal must be kept constant to ensure repeatable measurements.

Any variation in probe placement can introduce geometric measurement errors, especially on wide prismatic cell terminals.

Industrial Benefit

Sourcing contracts often demand the use of this testing method to resolve disputes regarding cell quality and internal resistance specifications. Because the method eliminates contact resistance variations, it provides highly repeatable data that can be compared across different test sites and laboratories. This repeatability is essential for maintaining consistent quality across a global supply chain where cells are manufactured in one region and assembled into packs in another.