Study Of Methane Sensor Based On Spectrum Absorption

In this paper, a detection system with an optical fiber gas sensor is studied, based on the spectrum absorption characterization of methane. Different gas has its inherent absorptive spectrum because of its different molecule structure. When a beam of light with a characteristic wavelength, corresponding to the absorption peak of the gas, passes through the gas, a strong absorption will occur, and the absorptive intensity is related to the gas's concentration. The gas's species and concentration can be gotten by the detection of light absorptive intensity.The Primary methods of methane detection are introduced detailedly, including carrier catalysis, optical interferometry, photoacoustic spectrum, harmonic detection and differential absorption detection, by analyzing and comparing with these methods, studying their advantages and disadvantages, considering the current status and the developmental requirement, we select gas spectral absorption method as the theoretical foundation of this system. After studying near-infrared selectivity absorption theory of the gas and methane absorption spectrum in near-infrared field, considering the attenuation characteristic of the transport optic fiber, the absorption spectrum of methane gas has been confirmed. In the experiment, double-wavelength -single-path differential absorption detecting method is adopted , a kind of light-emitting diode (LED) is chosen to use in the design of this system, and a structure of filter disk is designed, which is driven by stepping motor, to achieve differential absorption detection. These eliminated the effect caused by instability of LED and excursion of photoelectric components and achieved the more steady real-time continuous detection of the methane concentration. In the circuit, a optical fiber gas sensing system is built up by adopting data acquisition card. When debugging the circuit, a special virtual instrument is designed using Labview7.1 software which can output directly data and wave, also simplify research and test experiment.In this dissertation, a theoretical design method is presented, with related circuit design and debugging implemented, and the feasibility of the system is validated by analyzing the experimental result.