Research On Ethylene Concentration Detection System Based On TDLAS Technology

Ethylene(C2H4),as a plant ripening hormone,ean not only promote the ripening of fruits and vegetables but also accelerate their aging.In the process of storage and transportation of fruits and vegetables after picking,the concentration of ethylene will directly affect the freshness.At the same time,ethylene is an important gas affecting atmospheric chemical properties and producing ozone(O3).It will cause a certain degree of environmental pollution;In addition,ethylene is flammable,it can be mixed with air to produce explosive substances and often used as an indicator of coal spontaneous combustion.Therefore,the detection of ethylene concentration is of great significance for the preservation of agricultural products,environmental protection and production safety.Tunable diode laser absorption spectroscopy(TDLAS)as a gas detection technology has the advantages of its high sensitivity,good selectivity,high spectral resolution.Based on TDLAS technology,this paper designed an ethylene gas concentration detection system.The main research contents are as follows:1.On the basis of the principle of gas absorption,the basic theory of TDLAS technology was studied.By comparing the direct absorption and wavelength modulation method,this paper explained the advantages of wavelength modulation technology,and then gave the basis of ethylene concentration measurement based on TDLAS technology,and selected the ethylene gas absorption spectra.2.This paper designed the ethylene gas concentration detection system and analyzed the function and parameters of the main components of the detection system.Then,it analyzed the second harmonic absorption signal and its characteristic value of the laser at different temperatures,and gived the working parameters suitable for the system.3.Aiming at the designed ethylene gas concentration detection system,this paper built a simulation model of the detection system based on MATLAB simulation software to simulate the direct absorption and harmonic detection signals,and analyzed the source of the system noise and studied electronics and optical noise.It simulated thermal noise,shot noise,laser relative intensity noise and optical stripes.By comparing the noise processing effect of four filtering algorithms,it selected the best filtering algorithm to study the characteristic curves of harmonic signals with different noise amplitude and optical fringe spacing.By studying laser linewidth characteristics,we proposed a method to solve the influence of laser linewidth on the gas absorption line,which provides a theoretical basis for processing the subsequent data and improving the detection accuracy of the system.4.This paper realized the collection and processing of ethylene gas concentration data through the design of Lab VIEW monitoring software,The data processing flow of scanning period alignment,error analysis and elimination,periodic signal averaging,data filtering and background subtraction was established and detected multi-concentration ethylene gas.In this paper,50 ppm ethylene was used as a reference signal to detect the unknown concentration of ethylene.By means of least square method for fitting,the concentration inversion of ethylene gas was realized.