All RTDs are based on the change in resistance due to the temperature coefficient of resistance (TCR) of the metal being used. The resistance of a conductor of length $L$ with constant cross-sectional area $S$ and conductivity $\sigma$ (Figure 3.1) is
$$ R = \frac{L}{\sigma s} $$The conductivity of the material itself is temperature dependent and given as
\begin{align} \sigma = \frac{\sigma_0}{1+\alpha\left[T-T_0\right]} \end{align}Equation (1) stands for ...
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