Gas Recognition And Concentration Detection Based On Spectral Absorption Gas Sensor

At present,the spectral absorption gas sensor is the most mature in the optical gas sensor market,and has a large share in the market.Among them,Tunable semiconductor laser absorption spectroscopy?TDLAS?has become the main working principle of gas detection spectral absorption sensor because of its adjustable light source scanning range,short response time,high sensitivity,stable operation,relatively simple fabrication and relatively low cost.In this paper,TDLAS technology is used to identify CH₄,NH₃,CO and NO gas and detect their concentration by wavelength modulation harmonic detection.This paper starts with the gas absorption spectrum,introduces the principle and function of the gas absorption spectrum in the work of the spectral absorption gas sensor,then analyzes and compares the working principle,characteristics and defects of the direct absorption detection technology,the wavelength modulation harmonic detection technology and the photoacoustic spectrum detection technology from three kinds of spectral absorption detection technology.According to the comparative analysis of the response time,sensitivity and cost of the three detection technologies,the wavelength modulation harmonic detection technology is selected as the basis of the gas concentration detection research of the spectral absorption gas sensor.This paper starts with the important components of the spectral absorption gas sensor,and divides it into optical module,electrical module and data processing module.The main components of the optical module include light source,optical absorption cell and photoelectric detector;the electrical module includes the current modulation circuit,temperature controller,lock-in amplifier circuit,low-pass filter circuit and the transmission of collected signal and upper computer for wavelength modulation of light source;the data processing module includes gas identification Design and algorithm design of gas concentration detection.After in-depth study of these three modules,DFB laser is selected as the light source to emit light of specific wavelength,white absorption cell as the optical absorption cell to absorb gas,pyroelectric detector as the photodetector to receive the change of optical signal and convert it into electrical signal,the selected photodetector can initially amplify the electrical signal before outputting the signal;the current modulation circuit is advantageous The injection current is modulated by triangle wave and sine wave,and the modulated signal is transmitted to the laser by time division multiplexing.At the same time,TEC thermoelectric cooler is selected for temperature control.The second harmonic signal is extracted by designing a lock-in amplifying circuit to collect the data of harmonic detection.Finally,the harmonic signal is used for gas identification and concentration detection.The gas recognition and concentration detection system designed in this paper has been tested,and the success rate of gas recognition and the accuracy rate of concentration detection have been analyzed.The results show that the system maliciously carries out good gas recognition and high-precision concentration detection.At last,the paper analyzes the parts that are not considered in the design of the system,and puts forward the improved test for the performance of the detection system.