Detection Of Trace Gas Concentration Based On Photoacoustic Spectroscopy

Infrared laser photoacoustic spectroscopy has many advantages in terms of high sensitivity,fast response,strong anti-interference ability,wide detection range and so on.Now it has been widely applied to trace gas detection.There are various types of trace gases in the environment that we live.The qualitative and quantitative analysis of these gases has very important significance in the field of manufacture and production,biomedicine,and environmental detection.In order to meet the demand of trace gas concentration detection,a set of instruments for trace gas concentration detection was developed by photoacoustic spectroscopy.And an experiment was conducted to measure the concentration of ethylene gas.The main research contents are as follows:1.The paper detailedly analyzed the principle of infrared spectrum absorption theory and the basic principle of the detection of trace gases by photoacoustic spectroscopy.Based on the theoretical analysis,the relationship between the photoacoustic signal and the gas concentration is established,which establishes the foundation for the subsequent study on the measurement of the concentration of ethylene gas by photoacoustic spectroscopy.2.Based on the demand of measuring the concentration of trace ethylene gas,a set of photoacoustic spectroscopy gas detection equipments were developed.According to the absorption spectrum of ethylene gas in the near infrared,DFB semiconductor laser was selected as radiation source which has a range of advantages including compact structure,long service life,fast response,good monochromaticity,and reasonable price etc.A first-order longitudinal resonant cylindrical photoacoustic cell was used.On the basis of the theory analysis,detection sensitivity of the instrument is effectively improved through the optimized design of the size of the photoacoustic cell;Sound signal was detected by a durable microphone that has both strong stability and compact structure.The electrical system of the instrument is proposed and designed.3.The ethylene gas under different concentrations were measured by the use of the instrument that had developed;Through the experiment,the effect of temperature and pressure on the sensitivity and accuracy were determined;After proposed the correction method of temperature and pressure,the error of the measurement results is less than 3ppm;When compared the newly-developed instrument with the gas chromatograph,the experimental results show that the measurement accuracy is basically the same.As for the measurement time,the latter one spent more than 50% than the former one which is more suitable for engineering application.