Ultrasound Tab Welding Microstructure and Joint Resistance Limits
Ultrasonic tab welding balances acoustic softening and static clamp force to break interfacial oxides, yielding sub-5-micro-ohm joints without foil cutting.
Kelvin Four-Point Sensing
Meaning
Electrical measurement techniques using separate pairs of electrodes for current sourcing and voltage sensing eliminate the influence of lead and contact resistance. This methodology employs four distinct probes to provide an accurate reading of the internal resistance in battery cells or the quality of welded joints. Two leads carry the test current while the other two measure the potential drop across the component, ensuring that the resistance of the test equipment itself does not skew the results. kelvin four point sensing is the industry standard for characterizing high power lithium ion batteries where the internal resistance is often measured in milliohms.
It allows for the precise detection of manufacturing defects that a standard two wire multimeter would miss.
Measurement Precision
Separation of the current and voltage paths prevents the voltage drop in the test leads from being included in the measurement. This feature of kelvin four point sensing is necessary when testing the low resistance connections found in electric vehicle battery packs.
Calibration Accuracy
Testing hardware must maintain tight tolerances to provide repeatable data across different production shifts. Because kelvin four point sensing ignores the resistance of the probe tips, it remains accurate even as the test fixtures undergo wear and tear over time.
Quality Verification
Automated end of line testers use this technique to sort cells based on their electrochemical impedance. Using kelvin four point sensing ensures that every cell in a module has matched resistance characteristics, which is a requirement for maintaining pack balance during operation.