## 3 Results and Discussion  
### Temperature Loading  
Figure 4 presents the raw measured values. In Figure 4a, the measured temperatures show the behavior of the temperature control of the oven. After a new temperature value has been set, the oven needs up to 15 min to reach a constant temperature level. The differences between the PT100 sensors just after a new temperature has been set due to the airflow inside the oven and the different location of the temperature sensor. At lower temperatures, the two PT100 sensors show a difference in the measured values of about 0.02 \({}^{\circ}\)C, which increases to about 1.97 \({}^{\circ}\)C or 1.64% at 120 \({}^{\circ}\)C. For further evaluation, the data of the sensor attached to the surface of the specimen was used. Figure 4c presents the measured values of the T300 ex-PAN samples. The curve looks like an upside down version of the curves in Figure 4a since the CFSs reduce their resistance with increasing temperatures. An offset of the resistance values of about 0.02 \(\Omega\) can be seen. The curves in Figure 4d of the 70 A ex-pitch CFS show quite similar behavior to the curves in Figure 4a. The measured values are smaller since the ex-pitch CFSs have a much lower resistance of about 3.1 \(\Omega\) in comparison with the 27.3 \(\Omega\) resistance of the T300 CFS. An increase in resistance with an increase in temperature can be observed for the 95 A CFS in Figure 4d. This effect is more pronounced with higher resistance values before the temperature measurement and can probably be attributed to pre-damage at the electrical contact point during manufacturing (see Section 3.3). No further examination was made of 95A-CFS. \begin{table}
\begin{tabular}{c c c} \hline \hline
**Material of CFS** & **Specimen Nos.** & **Placement of CFS** \\  & & **between Layers** \\ \hline T300 1000-50A & 12, 13, 14, 15 & 1 and 2 \\ YS-95A-30S & 14, 16, 17 & 1 and 2 \\ YSH-70A-30S & 10, 11, 12, 13 & 1 and 2 \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Overview of the specimens for temperature tests. The T300 samples show a resistance drop of 3% (0.8 \(\Omega\)) while the 70 A samples show a drop of 8.5% (0.3 \(\Omega\)) at a temperature level of 120 \({}^{\circ}\)C. This means that the effect of the temperature on the fiber resistance is greater for 70 A than for T300-CFS. For practical applications, it is necessary to calculate the linear fit model from the measured data. For this purpose, the measured values were taken between 15 min after setting a new temperature and the next increase in temperature. For each temperature level, the mean values of the measured temperature were calculated and were used for the linear fit model (see Figure 5). Figure 4: Temperature dependence of the measured electrical resistance of the investigated types of CFSs: (**a**) PT100 temperature sensor, (**b**) CFS type 95A, (**c**) CFS type T300, (**d**) CFS type 70A. Figure 5: A linear fit function for the measured mean values of the CFS. A linear fit model was chosen, seen Equation (2), with the slope of the linear fit \(m\), the resistance at 0 \({}^{\circ}\)C of the CFS \(R_{0^{\circ}C}\), and the measured resistance of the CFS \(R_{T}\). \[T_{CFS}=(R_{T}\ \text{-}\ R_{0^{\circ}C})/m. \tag{2}\]  
The calculated coefficients of the linear model, and also the R\({}^{2}\) and root mean squared error (RMSE) values, are summarized in Table 4. The high R\({}^{2}\) values show, that the CFS signals show good linear behavior. The RMSE values show the magnitude of the error between the linear fit function and the measured mean values of the CFS samples. For an evaluation of the cyclic experiments and also for the possible practical utilization of the CFSs, it is necessary to evaluate a possible \(\pm 3\)\({}^{\circ}\)C change in temperature. This corresponds to an increase of \(\pm 0.1\%\) in the relative electrical resistance for a CFS made of T300 material and of \(\pm 0.3\%\) for a CFS made of 70 A material (calculated for an averaged value of \(m\) and \(R_{0^{\circ}C}\) from the measured data).