Theory Modeling And Design Implementation Of Methane Sensor Based On Correlation Spectroscopy And Broadband Light Source

At present, the effective monitoring, prediction and control of flammable, toxic or harmful gases is one of the important problems to be urgently settled; in the coal, chemical, oil, electricity and other departments, especially in terms of energy production and transportation. It has become an important problem to be solved how to reduce their threats to the production process and human health, and monitor, control and predict its evolution and development trend. Therefore, the research of all kinds of gas detection method has become a particularly important topic in the field of sensing technology. In this paper, the systematic research has been carried out to the methane gas concentration measurement, based on the infrared correlation spectrum of broadband light source. The main contents include:(1) Introduce the theory of the vibration spectrum, the rotation spectrum, the rotation-vibration spectrum, and the line shape and line width of the absorption spectrum of molecules, and analysis and correct the general equation of gas absorption based on the spectroscopy transition mechanism of gas molecular. Finally, the detection wavelengths of methane absorption spectrum were determined, the infrared absorption of the multicomponent gas under the general condition combining the HITRAN database was simulated, and the correlation spectroscopy methane sensor model of the broadband light source was established, by the principle of correlation spectroscopy and the calculation method of gas infrared absorption spectroscopy.(2) Introduce the system overall design of the infrared gas sensor based on the technology of COSPEC, analyze the system requirements, and compare and select the infrared light source and photodetector of the system. Based on the design model of the infrared broadband light source by using optical simulation Tracepro software, the best lighting point position is simulated and tracked under the different reflector. Compared the simulation results of the gas light sensing part with the measurement results of light absorption in actual situation, the optimum length of the sample chamber is determined, the structure of sensing chamber is optimized and the parameters is selected. Finally, the hardware and software based on virtual instrument test system are introduced.(3) By analyzing the interference factors of the spectral absorption on methane detection, the extraction technology of weak signal feature and the evaluation index of extraction algorithm, we have proposed the method combining FFT frequency domain filtering and Savitzky-Golay digital filter to process the spectral absorption data. It greatly improves the sensitivity of absorption spectrum (signal-to-noise ratio) and provides the reliable data security for accurate inversion of gas concentration.(4) For the self-developed methane gas sensing system, the principle and algorithm of calibration are further expounded, methane gas concentration inversion curves under the atmospheric pressure and tempreture were determined; Through simulating the influence of environmental factors, such as temperature, pressure, on the output using HITRAN database, the self-correcting of temperature effect has been realized by means of temperature compensation; For gas sensing system, it has been carried on to the detailed research and evaluation of the experimental system, including the response time of the experiment, sensitivity, cross interference experiment and stability experiment. The experimental results show that the system has high precision and stability, which verify the feasibility of the system for detecting methane concentrations.