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Why do we need to have a reference temperature to define thermal coefficient of resistance (TCR)?

TCR is the change in resistance per change in temperature divided by the resistance at a specified, fixed reference temperature:

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  • $\begingroup$ Because it varies with temperature, so you need to know if you are close to where the value is quoted or you have to find a better value for your temperature of interest. $\endgroup$
    – Jon Custer
    Jul 14, 2017 at 0:42

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The thermal coefficient of resistance is the derivative of resistance with respect to temperature or $\alpha=\frac{dR}{dT}$.

However this coefficient changes with temperature! So obviously you can only give the coefficient at a given temperature, unless the resistance is perfectly linear in T for all temperatures (no material has such a property). In other words, $\alpha$ is itself a function of $T$.

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