The System Of Fiber Grating Demodulation Based On Embedded

Compared with the traditional electrical sensor,fiber grating sensor has the features such as strong electromagnetic interference resistance,corrosion resistance,high precision,simple structure and low cost and so on.The fiber grating sensor has a wide range of applications in petrochemical,aerospace,building structure,and other fields.The key of fiber grating sensing technology is fiber grating demodulation system.Therefore,it is of great significance to develop a low-cost and high-precision demodulation system for the practicality of fiber grating sensors.In this paper,the five kinds of fiber grating demodulation methods are compared and analyzed in detail from the theoretical research of fiber grating sensors,and the tunable fiber Fabry-Perot(FFP)filter is selected as the demodulation method of the system.Then this paper designs the overall solution of demodulation system.According to the overall design scheme of the fiber grating demodulation system,the hardware and the software of the fiber grating demodulation system are designed.Specific content as follows:On the system hardware design,the paper chooses the STM32F4 chip,and designs the tunable FFP drive amplifier circuit and the SD card hardware circuit,which solves the problem effectively that the F-P is driven by the capacitive load.On the system software design,the paper developed the SD card driver,DAC driver and ADC driver,and each module driver is debugged by the computer,so that the modules can achieve the desired state.And then transplant the u C/OS-III embedded real-time operating system and Fatfs file system,the use of operating system to manage the system hardware and software resources.In order to cooperate the use of the operating system,the paper designed a simple memory management.In data storage,the paper implements that The LCD screenshots of BMP format and AD samples values of TXT format are stored in SD through Fatfs file system.Finally,the graphical user interface is designed by using GUI graphics library,and the waveform data display is completed.In order to obtain a more accurate fiber grating reflectance signal,the parallel data acquisition method is applied to the acquisition of fiber grating spectrum for the first time,and the hardware and software design of three AD parallel work is completed,which improves the number of acquisition points of fiber grating reflection spectrum,Which laid the foundation for high precision and high rate spectral fitting.In order to further improve the measurement accuracy of the system,this paper implements the Levenberg-Marquardt(LM)algorithm in the embedded environment and is used to fit the reflection spectrum of the fiber grating to obtain the exact position of the peak of the reflection spectrum.At the same time,the paper uses the stress grating to calibrate the temperature grating sensor to complete the change of the ambient temperature to the sensing grating.Compared with the traditional scheme,the system independent on the PC which realizes the data acquisition and storage,and the fitting calibration of the fiber grating reflection wavelength.Based on the high-speed data acquisition scheme and the LM fitting algorithm proposed,the center wavelength drift of the demodulation system is less than 15 pm.Combined with the temperature sensing grating sensitivity coefficient ?=10.3 pm/ ?,the system demodulation temperature resolution is less than 1.5 ?.