Research On Quasi-distributed Fiber Bragg Grating Demodulation System

The fiber Bragg grating sensor is small and easy to integrate.It is used to measure the structural damage and internal defects of large civil engineering buildings.Using the characteristics of good stability,corrosion resistance,electromagnetic interference resistance,etc,the fiber grating is suitable for working in harsh environments.Fiber grating is used to measure the signal transmission through wavelength coding,so it is basically not affected by the fluctuation of light intensity,has strong anti-interference ability,and can use multiplexing technology to achieve distributed measurement.This topic used wavelength division multiplexing to build a hardware platform for quasi-distributed detection systems,and uses C++ language to design the host computer of the demodulation system based on the MFC application framework class.In order to realize the demodulation of the collected signals,the principles,advantages and disadvantages of the four demodulation methods were analyzed.Finally,the FBGA module based on the demodulation principle of the CCD imaging method was used to demodulate the collected signal.The mainstream multiplexing technology was introduced,and the advantages and disadvantages of various multiplexing technologies were analyzed,and the mature wavelength division multiplexing technology was selected to expand the access capacity of the sensor.In order to use the FBGA module to build a hardware platform for the quasi-distribution system,the main device modules of the hardware platform were introduced,and the appropriate experimental equipment was selected according to the experimental needs.And find out the reasons for the various problems in the experiment and actively solved them,the hardware platform of the quasi-distributed fiber grating pressure detection system was finally built.The upper computer of FBGA demodulation module was designed and developed in the software part of this subject.The modular design was realized.The communication between the host computer and the hardware is realized by the USB port,so as to transmit the data to the host computer for processing.The function of acquiring the peak wavelength was realized,and threshold filtering was performed on the acquired data to improve the detection accuracy of the system.Secondly,the Tee Chart control was used to realize the online dynamic display of the spectrogram and the sensor acquisition waveforms of each channel.The software design used multi-threaded programming technology to put data collection into multi-threaded execution,so that while performing other functions,signal collection can run normally in the background,increasing the peak wavelength collection speed.Finally,an experimental platform for pressure detection was built to verify the stable operation of the self-designed functional module of the host computer.Through the pressure comparison experiment on the bare grating and the packaged grating,it is found that the packaged grating is more sensitive,at the same time,the package also solves the defect that the bare grating is fragile and easy to break.Finally,the performance test of the quasi-distributed demodulation system based on FBGA is carried out,and through experimental analysis and processing of experimental data,the good stability and repeatability of the designed quasi-distributed fiber grating detection system is proved.