Wire-wound type resistors are often used as reference elements in high-precision electronic
instruments of industrial frequencies (50-60 Hz). One of the main factors in the measurement
uncertainty of these instruments is the "self-heating" affected drift of the built-in
wire-wound resistors. The materials, geometry, construction and the thermal environment
of the resistors determine the dynamics of the load-affected drift. This paper investigates
a thermal model that can be used for on-line estimation of the load-affected thermal
dynamic drift of commercially available encapsulated precision wire-wound resistors.
Using the suggested model, the achievable estimation error of the relative change
in resistance is below 10%. The model and the model-based on-line error estimation
allow reducing the measurement uncertainty of industrial high-precision calibrators
and extending the power range of standard resistors in laboratories.
