Question

Find the neutral temperature and inversion temperature of a copper-iron thermocouple if the reference junction is kept at 0°C. Use the data in the table (33.1).

Answer 1

Neutral temperature,
${\theta }_n=-\frac{a}{b}$
$$\begin{gathered} a_{CuFe}=a_{CuPb}-a_{FePb} \\ =2.76-16.6=13.84\mathrm{\mu V}°{\mathrm{C}}^{-1} \end{gathered}$$
$$\begin{gathered} b_{CuFe}=b_{CuPb}-b_{FePb} \\ =0.012+0.030=0.042\mathrm{\mu V}°{\mathrm{C}}^{-2} \end{gathered}$$

Thus, the neutral temperature,
${\theta }_n=\frac{-a_{CuFe}}{b_{CuFe}}=\frac{13.84}{0.042}=329.52°\mathrm{C}=330°\mathrm{C}$
The inversion temperature is double the neutral temperature, i.e. 659 $°$C.