Long Term Interconnect Creep and Weld Fatigue under Cyclic Thermal Load in Heavy Formats
Thermal expansion and cell swell induce cyclic shear stresses that trigger weld fatigue and interconnect creep, requiring compliance flexure loops.
Four Wire Kelvin Resistance
Meaning
Precision electrical metrology separates current force lines from voltage sense lines to eliminate lead and contact resistance errors during low impedance testing. A four wire Kelvin resistance measurement channels high current through outer force leads while measuring the resulting potential drop across inner sense leads using a high impedance voltmeter. Battery cell testing relies on this technique to measure sub milliohm internal DC resistances accurately.
Measurements ignore contact resistance at test probes.
Lead Isolation
Dedicated sensing circuits draw negligible current to prevent voltage drop across measurement leads. Performing four wire Kelvin resistance testing isolates the true internal impedance of conductive components.
Contact Elimination
Mechanical probe contact point resistances vary widely due to oxidation, surface roughness and clamping pressure variations. Performing a four wire Kelvin resistance test bypasses these interface voltage drops completely by sensing potential directly at the boundary of the device under test. Current delivery circuits carry test signals without contaminating sense voltage readings.
Measurement Accuracy
Sub milliohm validation demands microvolt resolution during high current pulse testing of battery pack busbars. Incorporating four wire Kelvin resistance protocols prevents false batch rejections caused by probe wear or fixture contamination. Instrument calibration requires periodic verification against zero ohm standards.