Design Of Optical Fiber Sensor Demodulation System Based On ARM And Its Application In Construction Project Monitoring

The text mainly researched a distributed fiber grating sensing net demodulator. Based on analyzing deeply the research's status quo at home and abroad, the text concluded the developing trend of the fiber grating sensor and several main problems which need solving in actual application. Furthermore, the text studied five aspects, such as the frequency reflection, signal demodulation, multiplexing addressing, the power design and the temperature compensation in the fiber grating sensing net.Firstly, beginning with the theory model of the distributed fiber grating sensing net, the text analyzed the fiber Bragg grating's sensing mechanism and founded the fiber grating sensing model. Then based on analyzing and comparing the advantages and disadvantages of several multiplexing technology and signal demodulation technology, it applied the mixed divided multiplexing technology which combined the optical frequency domain reflection multiplexing technology and wavelength divided multiplexing technology to solve the addressing problem of the fiber grating sensing net, used the tunable tape light source which is made of the broadband light source and the tunable optical filter to demodulate multiplexing signal, and made sure the feasibility of the system through the theory analysis and experiment research.Secondly the emphases of the text were the design of the signal demodulation, used the ARM smart chip LPC2214 to design the hardware demodulation circuit and realized it.Thirdly the text analyzed the principles and designed the devices of the distributed fiber grating sensing net's composed modules. Then based on the temperature response characteristic of the fiber grating, it proposed a kind of design scheme of using the reference grating to make the temperature compensation of the fiber grating sensing array, described the compensation principle and proved the feasibility of the method. Meanwhile we could conclude that the method not only realized the temperature compensation but also decreased the repeatability error of the fiber F-P tunable filter and the error which was made by the light source power fluctuate, detector noise and circuit noise.Lastly, the characteristic testing experiments of the fiber Bragg grating temperature and strain were done and the necessity and the feasibility applying the fiber grating sensing net into the geotechnical engineering safety monitoring were analyzed. The actual experiment research of using the grating array addressing demodulation into the geotechnical engineering safety monitoring was done, and all kinds of factors which influence the system measure precision and their solutions were described.