Design Of Multi-point Monitoring System For CH₄ Concentration Based On TDLAS

Tunable diode laser absorption spectroscopy（TDLAS）refers to that the gas will selectively absorb the laser with specific wavelength under specific temperature and pressure environment.By detecting the change of light intensity after gas absorption,the required measurement data such as concentration,temperature and pressure of the gas to be measured can be retrieved in real time.The detection of gas concentration based on TDLAS technology has the advantages of high sensitivity,fast response,non-contact and not easy to be disturbed by other gases.Based on the theoretical research of TDLAS direct absorption method technology,this paper independently designs and builds a methane gas detection device,and uses the designed gas detection sensor to build a multi-point methane gas concentration monitoring platform.The main contents are as follows:This paper first introduces the research background,significance and development status of methane gas concentration detection at home and abroad,then expounds the basic principle of gas molecular absorption theory,and carries out the simulation research of gas absorption system according to bill Lambert law.Using the Simulink simulation platform in MATLAB,the simulation modeling of TDLAS direct absorption method for detecting methane gas concentration is carried out,and the detection systems with different absorption linear functions are simulated,analyzed and compared.The results show that the gas absorption rate of the methane concentration detection system based on TDLAS using Lorentz line is higher than that using Gauss line and Voigt line.At the same concentration,the gas absorption rate of the former is 10.77% and 10.32% higher than that of the latter two absorption linear systems,respectively.The methane detection device is designed and manufactured,and the monitoring device structure composed of signal generator,laser,gas absorption cell,photodetector and other main parts is designed.Finally,the detection device is calibrated and experimentally verified with fixed concentration of methane.The experimental detection error is less than 7%,and the real-time and effective detection of methane concentration is realized.The methane monitoring sensor based on TDLAS technology obtains the concentration data of the node,uses Zig Bee technology as a wireless communication means to build a multi-point monitoring network,and uses C + + to write software to monitor the methane concentration through the host computer.Zig Bee communication test is carried out to test the alarm function of the equipment and verify the functional feasibility of the system.The platform has abnormal alarm function,curve display function,serial port management function and data statistics function.By changing the source code of the platform,simulate 100 nodes,generate virtual data,and test various functions of the platform under multiple nodes.The results show that the system designed in this paper is feasible and solves the problem of multi-point monitoring of methane gas concentration.It provides a reference for the selection of appropriate absorption linear function for the detection of methane gas concentration by TDLAS,and lays a foundation for the application of TDLAS in the detection of gas concentration.