The working principle of Fiber Optic Pyrometer is: In the low temperature area (below 400℃), the radiation signal is weak, the system turns on the light emitting diode (LED) to make the fluorescence temperature measurement system work. The light-emitting diode emits the modulated excitation light, which is coupled to the branch end of the Y-shaped optical fiber through the condenser, and the Y-shaped optical fiber is coupled to the Fiber Optic Pyrometer through the fiber coupler. The head end of the Fiber Optic Pyrometer is excited by the excitation light to emit fluorescence. The fluorescence signal is derived from the optical fiber, and is emitted from the other branch end of the Y-shaped optical fiber through the optical fiber coupler, and received by the photodetector. The optical signal output by Fiber Optic Pyrometer is amplified and processed by the fluorescence signal processing system to calculate the fluorescence lifetime and obtain the measured temperature value. In the high temperature area (above 400℃), the radiation signal is strong enough, the radiation temperature measurement system works, and the light emitting diode is turned off. The radiation signal is output through the sapphire fiber and the Y-type fiber, and is converted into an electrical signal by the detector. The system calculates the measured temperature by detecting the intensity of the radiation signal.

　　 The end of the Fiber Optic Pyrometer is doped with Cr3+ ions to achieve fluorescence emission when light is excited. The length of the doped part of the fiber is 8-10 mm. The outer surface of the end optical fiber is simultaneously plated with a black body cavity for radiation temperature measurement. (At this time, the ratio of the length to the diameter of the fiber black body cavity is greater than 10, which can meet the requirement of constant apparent emissivity of the black body cavity). It is worth noting that avoiding or reducing the mutual interference between the fluorescent emission part and the heat radiation part is very important to ensure the performance of the entire system.
　　 After analysis, it can be found that this interference is mainly manifested as:
　　1) The influence of the radiation background signal in the fluorescence signal on the accuracy of fluorescence lifetime detection,
　　2) The effect of the coating on the surface of the optical fiber on the fluorescence intensity,
　　3) The influence of Cr3+ ion doping in the Fiber Optic Pyrometer on the thermal radiation signal of the blackbody cavity.