Fig. 1. Relative error intruduced by using the Wien approximation in equation (2).

Fig. 2. Optical signal path per channel.

Fig. 3. Simplified schematic of the software structure.

Fig. 4. Radiation intensity distribution for the upper and lower temperature limit of the measuring range.

Fig. 5. Radiation intensity distribution for the lower temperature limit of the measuring range and diode sensitivity.

Fig. 6. Spectral transmissivties of the filters used and of water vapour at 1 bar and 300 K, HITEMP [14] data visualized using RADIS [15–18].

Fig. 7. Schematic of the pyrometer system design.

Fig. 8. Conceptual drawing of the sensor head placement in the oven wall with the cone of vision of the sensor head in red.

Fig. 9. Temperature estimation error.

Fig. 10. Comparison of estimated emissivity functions and real emissivity of kaolinite [23].

Fig. 11. Temperature-signal-relation comparison between experiment and simulation.