Research On High Temperature F-P Acceleration Sensing System Based On Sapphire Fiber

Vibration monitoring at ultra-high temperature has always been a difficult point in sensing field,and can be applied to various fields such as aerospace and hightemperature casting.Fiber Fabry-Perot(F-P)sensors have the advantages of high measurement accuracy,simple structure,anti-electromagnetic interference,and easy network multiplexing.However,it is limited by quartz fiber which cannot work at ultrahigh temperature,such as 1200℃.Therefore,this paper studies a high temperature fiber F-P acceleration sensing system based on sapphire fiber.The main work of this paper is as follows:1.Based on the study of the characteristics of various fiber-optic accelerometers and the research status at home and abroad,the necessity of high-temperature fiber accelerometer is illustrated,and a high-temperature F-P accelerometer system based on sapphire fiber is proposed for vibration measurement.2.In this paper,the typical structure of fiber F-P sensor is introduced.Based on the principle of multi-beam interference,the two-beam interference of fiber F-P cavity is theoretically modeled and simulated,and the influence of cavity structure parameters on the output interference spectrum.And the demodulation method and principle of fiber F-P sensor are introduced.3.In this paper,a SiC vibrator based on micro-electro-mechanical system(MEMS)technology is designed.The F-P cavity is composed of vibrator and sapphire fiber,and the fusion process of sapphire fiber and multimode fiber is studied.Moreover,the package structure of high temperature sapphire fiber F-P accelerometer probe was designed and fabricated.And the inter-mode interference effect of sapphire fiber was introduced and simulated.The characteristics of interference spectrum of sapphirebased fiber F-P cavity were studied.4.Based on the spectral characteristics of the high temperature fiber F-P accelerometer,the intensity demodulation algorithm is optimized.The manual quiescent operation point(Q-point)switching function based on tunable narrow-band light source is designed.Aiming at the problem of Fabry-Perot cavity length change at high temperature,the Q-point automatic tracking algorithm is designed to overcome the problem that the static working point shifts out of the linear working area during high-temperature measurement,and can achieve accurate demodulation at high temperature.5.The high-temperature accelerometer experimental system was built to study the measurement performance of sapphire fiber F-P acceleration sensing system under room temperature and high temperature,and analyze the frequency measurement accuracy,stability and amplitude characteristics of the system.The experimental results show that the frequency response of fiber ultra-high temperature acceleration sensing system is well in the working frequency from 100 Hz to 1000 Hz at room temperature and 1200℃ high temperature,and the relative error of frequency measurement is kept below 1.56%,and the measurement accuracy is high.The on-site vibration testing experiment at high temperature was carried out in the foundry of Wuhan Heavy Machine Tool Plant,and the experiments show that the high-temperature F-P acceleration sensor system based on sapphire fiber can realize vibration measurement at ultra-high temperature.