Meaning
Electrical measurement technique that separates the current-carrying leads from the voltage-sensing leads to eliminate the resistance of the test cables. In low-impedance environments, four probe sensing provides a precise reading of the device under test by ensuring that no current flows through the measurement circuit. This method is the industry standard for characterizing battery cells where the internal resistance is often in the milliohm range.
It removes the contact resistance of the terminals from the final result. The accuracy of this configuration is what allows for the detection of subtle changes in the solid electrolyte interphase during long-term cycling.
Kelvin Connection
Contact between the probe and the cell terminal introduces a small but variable resistance. By using four probe sensing, the voltmeter measures the potential difference at the exact point of contact. Because the voltmeter has very high input impedance, the current in the sensing loop is essentially zero.
Such isolation ensures that the voltage drop across the sensing leads does not contaminate the data.
Resistance Elimination
Test leads and connector pins possess their own inherent electrical resistance. Without four probe sensing, these values would be added to the internal resistance of the battery, leading to an overestimation of losses. Resistance mismatch is particularly problematic in high-capacity cells where the cell resistance might be lower than the lead resistance.
The separation allows for the use of long cables without loss of accuracy.
Instrumentation Requirements
Specialized hardware is required to maintain the isolation of the two circuits. Modern battery cyclers integrate four probe sensing directly into the terminal clamps. If the sensing lines are accidentally swapped with the current lines, the measurement will fail or produce massive errors.
Quality control protocols require periodic verification of these connections to ensure the integrity of the collected data.
