Metrological Drift in Precision Bulk Metal Foil Resistors
Bulk metal foil resistor drift stems from thermal stress relaxation and epoxy moisture swelling, manageable through hermetic packaging and thermal burn-in.
Four Wire Kelvin Measurement
Sourced Connection
An electrical resistance measurement technique utilizing separate pairs of current-carrying and voltage-sensing leads eliminates the influence of lead wire impedance. Applying a four wire kelvin measurement allows the test system to acquire the true potential drop across the unknown resistor.
Physical Execution
Current is forced through the outer leads from a high-impedance source while the inner leads connect to a voltmeter with high input impedance. Because the voltage circuit draws virtually zero current, the voltage drop across the sensing leads is negligible. This separation isolates the contact resistance at the probe tips from the measurement loop.
Precision Boundary
Accuracy in the milliohm and microohm ranges depends on the correct positioning of the test probes. A four wire kelvin measurement becomes less effective if the current and voltage probes are placed too close to each other on a wide terminal, as this alters the current density distribution. Test fixtures must hold the contacts at a fixed distance to secure repeatable results in a production environment.
Metrological Calibration
Certification of low-resistance standards requires traceable four-terminal measurements to guarantee the accuracy of secondary transfer standards. Thermoelectric voltages generated at the junction of dissimilar metals introduces measurement bias, which is mitigated by utilizing offset-compensated ohms or current reversal methods. The calibration laboratory verifies the measurement uncertainty under controlled environmental conditions.