Development Of A Self-Adaptive Infrared Methane Detection System

In the process of coal mining is prone to gas leakage,and the main component of the gas is methane.When the concentration of methane is at range of 4.9% to 16%,an explosion can be caused by flame.Therefore,the concentration of methane should be detected timely and accurately,which can effectively avoid accidents.Nowadays,there are many methods for methane detection.And the infrared absorption method has many advantages,such as high sensitivity,good selectivity,fast response,long life,low cost,zero drift,etc.Therefore,it is practical significance to develop a high sensitivity infrared gas detector.However,there is some noise with unknown statistical properties under the mine,such as large machine start and stop,temperature,wind speed changes,and so on.For filtering out the noise,a modern filtering method is introduced which is adaptive filtering technique.The adaptive filtering technique is used to estimate the statistical properties of the noise and adjust the parameters of the filter in real time,which can eliminate the noise better and realize the accurate measurement of the methane concentration.In this paper,we first derive the theoretical innovation which is the principle of the two step method of gas detection,and design the optical part of the system.Then,the adaptive detection model for the system is designed,and two kinds of adaptive filtering algorithm of LMS and FTF using MATLAB are analyzed.The simulation results show that the FTF adaptive filtering algorithm has obvious advantages.Therefore,the adaptive filtering system designed in this paper uses the FTF adaptive filtering algorithm.Then the innovative adaptive infrared gas detection system of four channels based on two light and two detectors is put forward,and the whole hardware of the detection system is designed and produced,including optical,hardware circuit,data acquisition card and IPC(Industrial Personal Computer).Then two kinds of software programs of the detection system are designed by using LabVIEW software,which contains DAQ assistant,MathScript and other modules.Two kinds of Lab VIEW programs are used to measure the concentration of methane by using the traditional infrared method and the adaptive infrared method in the presence of noise.Finally,the software and hardware are integrated into an adaptive infrared methane detection system based on data acquisition card,IPC and Matlab,LabVIEW platform,and the gas detection experiments are carried out respectively.For the gas detection experiments without environmental interference,in range of 0 to 40000 ppm,the calibration curve fitting is 99.838%,the absolute value of relative error is less than 10.2%.At the concentration of 0 ppm,the relative fluctuation range is less than 0.925%.For the gas detection experiments with environmental interference,in the same range,the calibration curve fitting is 99.606%,the absolute value of relative error is less than 17.15%,at the concentration of 0 ppm,the relative fluctuation range is less than 1.2%.The main innovations of this paper are as follows:1.The traditional theory of differential gas detection is improved,and the dual-step differential method by combining hardware and software is proposed.2.The modern filtering technology using FTF adaptive filtering algorithm is introduced in the traditional infrared gas detection system,instead of the traditional filtering methods,which can better filter out the unknown statistical characteristics of under the mine.3.The AS-WJC adaptive infrared gas detection system based on data acquisition card,industrial personal computer(IPC)and LabVIEW is integrated.