Development Of A Methane Gas Sensor Based On Infrared Difference Detection

Methane is a flammable and explosive gas, which is the constituent of gaseous fuel such as mashgas and natural gas. Widespread in the geological seam, methane is the first factor to threat to the safety of coal mine. Therefore, we need to develop a detection method by which concentration of methane can be detected accurately in real time, which is significant to ensure the safety of coal mine.So far, there are many methods to detect concentration of methane. Interiorly the most common methods contains catalytic element method, the thermal conductivity method, optical interference method and infrared spectral absorption method. Infrared spectral absorption method is a new method developed in recent years and it is the product of spectral decomposition. The methane sensor based on infrared spectral absorption overcomes the deficiencies of traditional sensors and achieves the object of fast-response, long lifetime and long calibration cycle. In infrared absorption detection of methane, the key to improving detecting precision is to compensate the errors. Various differential absorption techniques are usually adopted to compensate the errors, which reduce different kinds of interferences.On the basis of infrared differential detection, a dual-wavelength difference methane sensor was designed. A rotating Filter controls filtering and passing through of the light, which makes the detecting light and reference light pass through the optical path in a time-sharing way. So, the sensor structure is of single-source single-light-path and single-detector, eliminating the errors caused by the source power fluctuations, the light-path loss and the detector instability.The main work is as follows:(1). Expounded the most common methane detected methods are expounded, done a comparative analysis of merits and faults of these methods, and emphasized the detect mechanism of the infrared absorption method.(2). Elaborate the common harmonic detection and differential absorption techniques to compensate the errors, emphasized several common differential detection. Compared these detection, we adopted the dual-wavelength difference detection.(3). An modifiedDesign alternative of dual-wavelength difference methane sensor was elaborated. By using a rotating Filter with four point, a single-source single-light-path and single-detector structure has been achieved, eliminating the error caused by the detector instability. Designed a semi-open and multipass Gas cell so that the system sensitivity can be adjusted dynamically as required. (4). Calibrated the sensor using a set of standard gas, polyfited the detecting result with MATLAB. Conducted the concentration contrast and stability experiment and analyzed the experiment results.