Research On The Online Detection System For Trace Gas Component Based On Spectroscopy Technology

Environment pollution is one of the most important problems in the world.It is significant in reality to monitor the polluted gases in the air,especially trace gases.At present,trace gases are often used in industrial procedures as it is flammable and explosive.Detecting trace gases becomes necessary gradually.The traditional chemical measure not only has the complicated measuring process,but also takes long time to sample,the measurement precision and speed cannot meet the current needs of real-time monitoring of trace gases.While Spectroscopy method,especially tunable diode laser absorption spectroscopy(TDLAS),has the advantages of fast,high sensitivity,high selectivity and continuous on-line monitoring.Ethylene is one of trace gases in industrial production,this paper based on the detection of ethylene concentration as the main research object.The system has comprehensive prospect on detecting density of other trace gases by changing the light source.Wavelength modulation method(WMS)is one of the TDLAS techniques.Designed the system,this paper combined WMS with long path gas absorption cell to improve the measurement accuracy of the system.Firstly,after the absorption spectra of ethylene were analyzed,taking into account the requirements of the detecting sensitivity,Trace analysis of ethylene absorption line choice was completed,which ethylene absorption line was near the wavelength of infrared 1626 nm.Secondly,based on the absorption spectrum of the ethylene crossover interference problems,the ethylene gas concentration calibration test used wavelength modulation.Wavelength modulation and harmonic detection method cannot influence the background line offset,with strong anti-interference ability.Finally,according to the influence of temperature and pressure change in the measurement environment on the results,the experimental analysis is carried out.The intensity and line width change of gas spectrum were tested at different temperatures and pressures respectively.According to the test results,the correction coefficients of temperature and pressure to the test results are obtained.In this paper,the noise reduction of the experimental data is processed to reduce the interference of background noise,which is helpful to improve the sensitivity and accuracy of the system.The concentration inversion in this system is carried out on a computer,and the method is linear fitting to extract the single absorption line signal.Lab VIEW graphic software is used to complete the software design of the host computer,programming control of the laser driver,real-time data acquisition,storage and processing,calculation of gas concentration,etc …...