SOTA precision thin film chip resistors have resistance tolerances of [+ or -]0.1, [+ or -]0.25 and [+ or -]0.5% and/or temperature coefficient of resistance
of [+ or -]25 and [+ or -]50 ppm/[degrees]C.
where [[rho].sub.e] is the initial resistivity of the sensor at room temperature measured in [OMEGA] x m, L is the length of the conductor in m, Ac is its cross-sectional area in [m.sup.2], a is the temperature coefficient of resistance
for the layer measured in 1/K, and [DELTA]T is the change in temperature of the layer from room temperature.
Temperature variations and exposure to high temperatures play an important role in long-term stability; relevant parameters include temperature coefficient of resistance
(TCR), self-heating characteristics, and thermal electromotive force (EMF).
It is both a function of its base resistance and its temperature coefficient of resistance
. A sensor with higher stability is not necessarily more accurate, but the larger signal it produces will tend to be less susceptible to lead-wire effects and electrical noise, as it generally improves the signal-to-noise ratio of the sensor interface.
The Temperature Coefficient of Resistance
was determined experimentally, according to the following equation
* Thermal coefficient of resistance
may significantly reduce throughput performance and final process tolerances.
The voltage coefficient of resistance
(VCR) is a measure of non linearity of resistors and is defined as the sensitivity of resistance.
During selection of heater material, the resistivity, temperature coefficient of resistance
, melting point, density, heat capacity, thermal conductivity and corrosion resistance were mainly considered, and their respective effect on the heater could be evaluated through temperature distribution.
where: [S.sub.i] express the coefficient of resistance
This material is well suited for precision resistors because of its very low temperature coefficient of resistance
near room temperature as well as its small offset relative to copper in the thermoelectric series.
Cupronickel has a low temperature coefficient of resistance
(TCR), so the heater resistance will change very little as the temperature goes up and down.