Research On Concentration Detection Technology Of High-Precision Toxic And Harmful Gas Based On TDLAS Technology

Tunable semiconductor laser absorption spectroscopy?TDLAS?is one of the most developed high-precision toxic and harmful gas concentration detection technologies.TDLAS technology has many advantages such as narrow light source line width,fast response speed,high detection sensitivity,strong anti-interference ability,low cost and low power consumption.Therefore,it is widely used in the field of high-precision toxic and harmful gas concentration detection by domestic and foreign research institutions and manufacturers.Based on the in-depth study of TDLAS technology,this paper designs a prototype of multi-component high-precision toxic and harmful gas concentration detection system that can simultaneously measure seven kinds of toxic and harmful gases such as CO,HCl,NO,NH₃,CH₄,CH₃COCH₃ and HCHO.Firstly,this paper analyzes the detection principle of TDLAS technology in detail,and compares two methods of concentration detection based on TDLAS technology:direct absorption differential detection?DOAS?and wavelength modulation harmonic detection?WMS?.Direct Absorption Differential Detection?DOAS?is suitable for high concentration detection?concentration is on the 1%level?,while wavelength modulation harmonic detection?WMS?is suitable for low concentration detection,high sensitivity,concentration detection accuracy can reach ppm or even more Low level,Since this paper is aimed at the detection of low-concentration toxic and harmful gases at the ppm level,WMS technology was chosen as the theoretical basis for the prototype design of the actual multi-component high-precision gas concentration detection system.This paper starts with the various components of the prototype,and deeply studies the working principle and design scheme of the four modules of the light source control module,gas absorption module,signal receiving module and data processing module.The light source control module modulates the DFB laser with a current modulation method using a low frequency triangular wave and a high frequency sine wave superposition,and the TEC thermoelectric cooler performs temperature control;the gas absorption module is designed with an anti-interference FP filter for shielding thermal radiation and electromagnetic radiation.The signal receiving module uses a digital lock-in amplification algorithm instead of the traditional lock-in amplifier hardware to eliminate hardware noise interference,and has maintainability and expandability.The host computer software of the data processing module is written in the MFC framework and has good performance.Human-computer interaction experience,real-time monitoring of gas concentration,calibration of zero points and acquisition of data.In this paper,the prototype test is carried out,and four key parameters of concentration detection accuracy,single-point spectral response time,nonlinearity and concentration detection range are analyzed.The results show that the prototype can realize high-precision detection of low concentration of 7 kinds of toxic and harmful gases.Finally,the insufficiency of the performance of the prototype is analyzed,and the improvement of the performance of the prototype system is proposed.