Acceptance Quality Limit Sampling Plans for Lithium Cell Receiving Facilities
Enforce ANSI ASQ Z1.4 Level II sampling with AQL 0.010 for critical safety flaws and Kelvin OCV IR screening to reject defective lithium cells at receiving dock.
Four-Wire Kelvin Fixture
Meaning
Electrical testing apparatus utilizing separate current and voltage paths eliminates the effect of lead and contact resistance on measurements. By employing a four-wire kelvin fixture, test engineers can acquire highly accurate resistance values for low-impedance battery cells. This hardware ensures that the measurement reflects only the internal resistance of the cell rather than the impedance of the test leads.
Resistance Measurement
Measurement accuracy is critical for sorting cells into matched groups for pack assembly. Within a four-wire kelvin fixture, two leads apply a known test current while another two leads measure the voltage drop across the cell terminals. This configuration prevents voltage drops in the current-carrying leads from distorting the measured potential.
Contact Interface
Physical contact with the cell terminals must be clean and consistent to ensure stable readings. The gold-plated pins of a four-wire kelvin fixture are spring-loaded to maintain a reliable force on the battery terminals. This design helps cut through surface oxides and contaminants.
Production Line
High-speed sorting lines use these fixtures to evaluate thousands of cells per hour. Integrating a four-wire kelvin fixture into automated test nests ensures fast and reliable data collection. The measured internal resistance is used to filter out cells with defective welds or internal assembly errors.
This helps ensure that the final pack maintains uniform cell characteristics and stable thermal behavior during operation. When the contact is repeatable, the rejection rate due to measurement error drops below a fraction of a percent, protecting overall production yield.