Research On Methane Gas Concentration Measurement System Based On Fiber Bragg Grating Sensing Technology

Methane is the main component of gas.When the methane concentration in the air reaches the gas explosion limit,it will explode when it encounters an open flame or a high-temperature heat source.In recent years,gas explosion accidents have not only brought huge losses to national enterprises and personal properties,but also brought major social security risks.Therefore,timely and accurate measurement of methane concentration is extremely important for preventing gas explosions and safe production in mines.In the process of methane concentration measurement,factors such as external environmental interference and instability of the gas chamber will cause errors in the system measurement.In response to these problems,this paper aims to accurately detect the concentration of methane gas,combined with fiber grating sensing technology and the principle of infrared spectroscopy to design a detection system suitable for low-concentration methane gas measurement,which realizes accurate and stable measurement of methane gas and meet actual engineering needs.The main work of this paper is as follows:1.Based on the Lambert-Beer law,the second absorption line in the R(4)branch of the methane band is selected as the measured absorption peak according to the spectral absorption theory of methane combined with the bandwidth of the existing light source.According to the temperature-sensitive characteristics and filtering characteristics of fiber gratings,a reference grating is added to the measurement system to replace the filter in the traditional measurement method,which solves the problem that temperature changes affect the precise measurement of gas concentration.2.Use SOLIDWORKS software to design the overall structure of the gas chamber,and then use ZEMAX software to simulate and optimize the light path in the gas chamber,and obtain the coupling efficiency of the gas chamber to the methane near-infrared laser up to 93.2%.The gas chamber is measured through experiments,the actual coupling efficiency of methane near-infrared laser reaches 92.8%,and the design of high coupling efficiency and high stability gas chamber is completed.3.According to the detection method of the system,combined with the actual situation,the device selection of each module of the measurement system is determined,and the design of the optical path and software function module of the measurement system is completed in combination with the device selection of the system.4.Set up a measurement system and perform system calibration.On the basis of the original calibration scheme,add temperature compensation algorithm.And perform the optical fiber link loss experiment,the optical fiber grating demodulator test experiment and the system comparison measurement experiment to prove the feasibility of the measurement system design,then the gas concentration measurement and the calculation of the system technical indicators are carried out.The measurement results show that the sensitivity of the measurement system is 0.02 m V/ppm,the stability of the measurement system is 0.12%,and the maximum measurement relative error is 0.149%.The displayed value of the system measurement is basically consistent with the theoretical value,and the measurement system has the advantages of high sensitivity,good stability,high precision,good repeatability and other advantages.