An Investigation On EFPI-FBG Based Pressure And Temperature Multiplexing Fiber Optic Sensor System

Extrinsic Fabry-Perot Interferometric(EFPI) optical fiber sensor and Fiber Bragg Gratings(FBG) have won widely attention for their small size,compact configuration,good reliability and flexibility.They can be widely used in most harsh environments,such as oil well,electric power industry and chemical industry.In this dissertation,A Fiber Fabry-Perot (F-P) Interferometer and a Fiber Bragg Grating(FBG) based pressure and temperature multiplexing sensor system is studied systematically.The main research works are outlined as followings:An accurate de-multiplexing mathematical model is established for optical fiber Fabry-Perot(F-P) cavity and Fiber Bragg Grating(FBG) multiplexed sensor.The spectral character of the F-P and FBG multiplexed sensor is analyzed and a new mechanism of separating FBG spectrum from F-P sensor spectrum is proposed.The validity of the method is verified by numerical simulation and experiment.With a swept laser based wavelength interrogator an experimental comparison between the accurate demodulated results and the directly calculated results is carried out,which shows a pretty good coincidence with the theoretically simulated results.The experimental results demonstrate that the cross interference between F-P sensor spectrum and FBG sensor spectrum is clearly eliminated,and the resolution of the sensor system is effectively improved with the new demodulation mechanism.The maximum uncertainty of 0.2nm and 0.7pm has been achieved for the F-P cavity length and FBG peak wavelength measurement respectively.A Fiber Fabry-Perot(F-P) Interferometer and a Fiber Bragg Grating(FBG) based pressure and temperature multiplexing sensor system is presented.This system is designed for high temperature oil well down-hole permanent monitoring of pressure and temperature. Connecting a FBG temperature sensor and a F-P pressure sensor in series in the sensor head, the sensor system combines the advantages of simple structure of FBG for temperature sensing and high accuracy and low temperature cross-sensitivity of F-P pressure sensor. Experimental results showed that the temperature measurement accuracy of 0.5℃and the long-term drift of the air gap of the F-P pressure sensor at 300℃is less than 0.1%within 300 hours time span.This indicates that a long-term pressure measured accuracy of 0.03MPa has been achieved in pressure gauge range of 0～30 MPa and in temperature variation range between 18℃to 300℃.