Design Of Methane Gas Detection System Based On Laser Absorption Spectroscopy Technolog

Methane is the main component of natural gas.As the use of natural gas becomes more and more common in cities,methane begins to enter people’s daily life.But methane is also a major contributor to greenhouse gas pollution.Therefore,the detection of methane gas can not only prevent the occurrence of accidents,but also effectively reduce the emission of methane gas,which is of great significance.The traditional methane detection methods with low precision and non-contact measurement,shortcomings and so on are greatly influenced by the environment,based on a tunable semiconductor laser absorption spectroscopy(TDLAS)technology of methane gas detection with high sensitivity,high selectivity,the characteristics of non-contact,real-time,has been widely applied in the detection of various gases in the atmosphere.A miniaturized methane gas detection system is designed based on TDLAS technology.Firstly,the basic theory of gas molecular absorption spectrum was studied and 1653.7nm was determined as the absorption peak of methane gas.By comparing the advantages and disadvantages of TDLAS detection methods,wavelength modulation technology is used to detect methane concentration in order to improve the accuracy of gas detection.Then,the hardware circuit of methane gas detection system is designed as a whole,focusing on the design of laser driving circuit and temperature control circuit.In order to build and experiment methane gas detection system,Simulink is used to simulate and analyze TDLAS gas detection system based on wavelength modulation and harmonic detection technology.Finally,the software program of the system is designed based on STM32.As the control and digital signal processing center of the system,STM32 mainly realizes the drive and temperature control of the laser,and focuses on the incremental digital PID algorithm of anti-saturation integral in temperature control.In the aspect of digital signal processing,the hardware FPU and software DSP library of STM32F407 series chips are used to amplify the reflected light signal and extract harmonic signal,which greatly improves the operation speed.Based on the software and hardware design of methane gas detection system,a system experimental platform is built.The driving circuit,temperature control circuit and phase-locked amplifier are tested and verified.Calibration experiments are carried out for methane gas with0～4% concentration,and the mean value of the corresponding first harmonic and the peak value of the second harmonic are measured.The least square method is used to fit the curve to invert methane gas concentration and achieve methane gas concentration measurement.