# Zero Drift Infrared Radiation Thermometer Using Chopper Stabilised Pre-Amplifier
## 3 Results and Discussion
### Characterisation of IRTs against a Blackbody Source at Low Temperatures  
Mean output voltages for the zero-drift IRT and precision IRT, as functions of blackbody source temperature, are presented in Figure 3a. The standard deviations of the measurements are represented by error bars. The zero-drift IRT measured 0.35 mV at 20 \({}^{\circ}\)C, increasing to 2.1 mV at 70 \({}^{\circ}\)C, whilst the precision IRT increased from \(-0.072\) mV to 1.4 mV over the same temperature range. Whilst both IRTs demonstrated the ability to resolve changes of target temperature over this measurement range, the standard deviation of the zero-drift IRT measurement was clearly lower across the full measurement range. The mean measurement tolerance of the zero-drift IRT output voltage over the temperature range measured was calculated to be 5.8%, whilst that of the precision IRT was 21.4%. These results reflect what was observed in Figure 2 and Table 1; the zero-drift IRT provides a more sensitive and less noisy measurement. \begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Condition** & **IRT Version** & \begin{tabular}{c} **Mean \(V_{o}\)** \\ **(V)** \\ \end{tabular} & \begin{tabular}{c} **Variance** \\ **(V2)** \\ \end{tabular} & \begin{tabular}{c} **Excess** \\ **Kurtosis** \\ \end{tabular} \\ \hline \multirow{2}{*}{\
\begin{tabular}{c} Zero \\ Signal \\ \end{tabular} } & Precision & \(-1.000\times 10^{-4}\) & \(1.906\times 10^{-9}\) & 416.2 \\ \cline{2-5}  & Zero-Drift & \(2.397\times 10^{-5}\) & \(8.558\times 10^{-10}\) & 121.4 \\ \hline \multirow{2}{*}{
\begin{tabular}{c} 700 \({}^{\circ}\)C \\ Signal \\ \end{tabular} } & Precision & 0.613 & \(1.645\times 10^{-4}\) & 1.22 \\ \cline{2-5}  & Zero-Drift & 0.616 & \(1.168\times 10^{-4}\) & 1.33 \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Mean, variance and excess kurtosis values of precision and zero-drift IRTs. Whilst the output voltage measurement variation reflected the capability of the thermometers to measure a stable signal, the overall measurement uncertainty included the capability to interpolate the temperature between known calibration points and the calibration tolerance of the equipment used. A more complete estimate of overall measurement uncertainties between 40 \({}^{\circ}\)C and 70 \({}^{\circ}\)C is presented in the following tables and analysis, thereby affording a more comprehensive understanding of the measurement tolerance of the two versions of the IRTs. The uncertainty budget for single measurements has been estimated, based upon the individual contributions from the equipment used in calibration and measurement and from the measurements acquired using each IRT. The individual uncertainty contributions considered in the estimate, which arose from the calibration equipment and measurements, are presented in Tables 2 and 3, respectively expressed in terms of absolute temperature and percentage of voltage. The largest individual contributions to the uncertainty arose from the stochastic variability in the IRT voltage measurements and the error arising from the interpolation used to convert between the voltage and temperature. The uncertainties that arose from the calibration equipment can be neglected without detriment, therefore we can simplify the uncertainty estimation by evaluating only the variability of the measurements and interpolation errors, presented in Table 3. The overall uncertainties of the IRT measurements, on this basis, varied from 2.5 K at 40 \({}^{\circ}\)C to 2.9 K at 70 \({}^{\circ}\)C for the zero-drift IRT and 11.7 K at 40 \({}^{\circ}\)C and 6.0 K at 70 \({}^{\circ}\)C for the precision IRT. To assess the linearity of the two IRTs, Figure 3b shows \(ln(V_{o})\) as a function of 1/\(T\). The zero-drift IRT adhered to the linear relationship expected between \(ln(V_{o})\) and 1/\(T\) better than the precision IRT,