Research On Fiber Bragg Grating Temperature And Strain Demodulator

Temperature and strain are important parameters that reflect the stress and health of the engineering structure,as well as important detection content for disaster warning and scientific management of critical infrastructure.In actual engineering applications,many parameters to be tested can be converted into temperature and strain variables for testing.Fiber Bragg grating detection technology is a relatively new detection technology.The detection principle of this technology is to use the temperature and strain sensitive characteristics of the center wavelength of the fiber grating to convert the temperature and strain of the environment in which it is located into wavelengths.In addition,fiber Bragg gratings have the advantages of long detection life,high detection accuracy,immunity to electromagnetic interference,strong corrosion resistance,and group detection networks.Fiber Bragg gratings are gradually popularized as temperature and strain detection sensors,and the demand for demodulation equipment is also increasing.The increase.At present,the existing demodulators on the market are expensive and some of their performance indicators cannot meet the needs of high-precision detection.Therefore,it is of great significance to develop a low-cost,easy-to-carry,low-power,high-demodulation accuracy fiber grating demodulator equipped with field application software.Based on the theory of fiber grating sensing technology,this paper analyzes and compares the existing demodulation schemes,selects the fiber grating demodulation scheme based on scanning laser,builds an experimental platform and completes the development of a multi-channel demodulation engineering prototype.This article mainly works in the following aspects:(1)Based on the theory of coupling modes,this paper studies the basic principles of fiber gratings,including: the photosensitivity,optical characteristics,sensing characteristics,temperature sensing characteristics and strain sensing characteristics of fiber gratings;the demodulation schemes that are currently widely used are studied.,Including: spectrometer detection method,edge filter detection method,matched grating detection method,scanning laser detection method and tunable FP filter method,compared several demodulation schemes,analyzed the advantages and disadvantages of each scheme.(2)According to the analysis and comparison of multiple demodulation schemes,this article chooses the scanning laser-based demodulation scheme,studies the system composition based on the scanning laser demodulation scheme and the components required for this scheme,selects the appropriate photodiode,and designs the amplifying filter circuit Analyze a variety of fitting algorithms,respectively apply: general polynomial fitting algorithm,Gaussian fitting algorithm,cubic spline interpolation algorithm,Voigt fitting algorithm and moving average fitting algorithm,select the most suitable moving average for this scheme Fitting algorithm.Perform three-step positioning and peak search on the fitted data,and calculate the center wavelength.(3)Based on the Microsoft basic class library,the upper computer software of the fiber grating temperature and strain demodulator is written.The software mainly includes the following functions: setting of scanning lasers and data acquisition cards,control of temperature,strain channels and gratings,and demodulation The window of the result displaying,and the historical inquiry function.The experimental program was integrated and a prototype was made.(4)The performance indicators of this prototype are analyzed,and the equipment used in the experiment is introduced.In order to verify the performance indicators of this demodulator,a series of temperature and strain test experiments were designed to separately measure the performance indicators of wavelength demodulation accuracy,system demodulation linearity,repeatability,system demodulation dynamic range,system demodulation capacity.The experimental results show that the wavelength demodulation accuracy of the prototype is±1pm,the wavelength demodulation stability is ±1pm,the wavelength demodulation resolution is 1pm,and the system demodulation speed is 1Hz.In addition,this paper also tested other sensors based on fiber grating structure: displacement sensor,soil pressure sensor and osmometer,and the test results performed well.