The Research Of Methane Concentration Detection System Based On Infrared Absorption Theory

The coal mine safety production has been the focus of China’s energy industry, but gas explosion accidents have taken lots of property from the country and been a horrible threat to people’s life safety. Currently most of gas concentration analyzer calibration used for determination of gas need to be improved in the real-time, stability and sensitivity, and some large foreign manufacturers and research institutions in this area have relatively mature product, but the price is expensive. A methane concentration detecting instrument is developed based on the absorption theory. Methane has a wavelength-selecting absorption to infrared radiation and the absorption is functional with the concentration of gas.Having analyzed and compared with many gas measurement methods and according to precision and working environment required, we select infrared spectrum absorption method as the theoretical way of this instrument. Refer to the characteristics of the incandescent lamp, LED and laser diode, incandescent lamp IRL715is selected as the light source. Its accessible wavelength range amounts from the visible up to about4.4μm. Having analyzed the property of detector, we select PYS3228as the gas sensor. It integrates two pyroelectric chips which convert the infrared radiation energy into voltage signal, having tow windows open on the package. The center wavelengths of two infrared filters are3.31μm and4μm, which are in front of two pyroelectric chips.According to the selected light source and detector characteristics, we design a reasonable source modulation circuit and signal processing circuit. STM32is taken as the core of the instrument, completing signal acquisition and processing, concentration conversion and sound light alarm. Based on the single chip computer, we design system power circuit, light source modulation circuit, basic amplifier, peak detector circuit, display circuit, light and beep alarm circuit, realizing each function through programming. When the detected gas concentrations are over the warning limit, which was set before, light and beep alarm signal is triggered. The gas absorption experiments, repeatability and stability experiments for detecting instrument are carried out. According to the experimental data, fitting curve and the error analysis and calibration results are given. The results proved the methane concentration detecting instrument based on infrared absorption theory has a relatively good stability and accuracy.