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.
Resistance Stability
Parameter Consistency
The ability of a material or component to maintain its specified resistance under varying environmental and operational stresses determines its accuracy class. Achieving high resistance stability is necessary for sensors and reference dividers where ratio tracking is critical.
Influence Factor
Temperature changes, humidity, mechanical stress and electrical load all contribute to irreversible drift in resistive elements. Over time, resistance stability is threatened by moisture absorption in protective coatings or oxidation of the resistive film. High-precision applications use foil or wirewound resistors that have been hermetically sealed or annealed to minimize these effects.
Sourcing Protocol
When qualifying components, the design engineer relies on standard tests to quantify drift under specific conditions. To verify resistance stability, the part is measured before and after exposure to thermal shock or damp heat. This measurement must use the same instrument and cable configuration to avoid introducing contact resistance errors.
Quality Standard
Calibration certificates indicate the maximum expected drift over a given time interval, usually one year. If the resistance stability does not meet the requirements of the circuit, the calibration frequency of the entire instrument must be increased. This raises the total maintenance cost of the equipment in the field.