## 4 Experiment and Result Analysis  
In order to verify the results of the three-wavelength radiation temperature measurement method based on reflection correction, an experiment was designed in a laboratory  
Figure 10: Variation in the error function e(T) with temperature T (green: 1600 nm and 1500 nm; red: 1700 nm and 1600 nm; blue: 1500 nm and 1700 nm). environment: a three-wavelength optical radiation pyrometer was used to measure the temperature of turbine blades in a heating furnace, and the three-wavelength radiation temperature measurement method based on reflection correction proposed in this paper and colorimetric temperature measurement methods were used to demodulate the blade temperature. The inversion results and the temperature errors of these methods are compared with those of thermocouples. The experimental device designed and built by our group is shown in Figure 11. Three vanes and a target blade were placed in a heating furnace with a uniform temperature distribution according to their actual position in the engine. The probe was installed on the guide rail, and radiation from different positions of the target blade and the adjacent blades was collected through the shift and rotation of the probe. The radiation from the target blade was reflected to the lens group by the mirror in front of the probe, then converged into the optical fiber by the lens group, and finally entered the three-wavelength optical system through an optical fiber. In the optical system, radiation collimated by a collimator lens was divided into three beams by two dichroic mirrors. The radiation at each wavelength is focused on the detector of the corresponding channel after passing through its own filter. The temperature is demodulated based on the voltage output by the detector. The center wavelengths of the three narrow bands of radiation are 1500 nm, 1600 nm, and 1700 nm, and their bandwidths are all 50 nm. During the experiment, the temperature of the heating furnace was increased to 650 \({}^{\circ}\)C, 700 \({}^{\circ}\)C, 750 \({}^{\circ}\)C, 800 \({}^{\circ}\)C, 850 \({}^{\circ}\)C, 900 \({}^{\circ}\)C, and 950 \({}^{\circ}\)C. After the temperature in the furnace was stabilized, the probe was inserted for measurement. Radiation from the target blade, three guide vanes, and the upper surface of the heating furnace was collected by the probe. The center of the trailing edge of the suction surface of the target blade (point \(P_{0}\) in Figure 6) was selected for temperature measurement. We collected the radiation from three points on the leading edge of the guide vane's pressure surface (the quarter point of the guide vane) and from the 2 \(\times\) 2 points on the upper surface of the heating furnace and took the average voltage signal of all points of each component to calculate the ambient radiation. In order to prevent overheating of the probe tip, which would allow thermal radiation from the reflector to interfere with measurement, the probe was withdrawn from the heating furnace after each measurement to be cooled with cold air. Although the distance from the probe to each blade is different, the temperature calibration results of a blackbody at different distances from the probe to the blackbody show that, as long as the temperature fluctuation of the surface to be measured is small and the object field of view of the radiation pyrometer is always full, changes in the temperature measurement distance hardly affect the output  
Figure 11: Radiation temperature measurement experiment of turbine blade. signal. Then, the measured radiation signals of the pressure surface of the guide vane and the upper surface of the heating furnace were substituted into Equation (20) to correct the reflected radiation of the target point.