Study Of Optical Fiber Sensing Technique For Harmful Gas Based On Spectrum Absorption

Along with the development of oil and natural gas industry, the coal mine exploding accident increased everyday. China is the country with the maximal coal yield and consumption, and also is one of the countries using coal as the most energy sources. Many kinds of inflammable and explosive gases such as methane(CH4)and carbon monoxide(CO) coexisting in the process caused a series of problem like the safety problem and environment pollution and so on. So it is very important to detect more sensitive the harmful gases engendering in the coal mine.Development of the communication technology has made the performance of the optical fiber parts more perfect. So, in all of gas sensor, optical fiber one has attracted wide interest by related researchers domestic or abroad. Especially optical fiber sensor is more safe and reliable, for electrical insulation has been realized by the separation of optical fiber sensor from detection and signal processing circuit. Aiming at the most harmful gases, methane and carbon monoxide in the coal mine, the dissertation takes deep research on the theory and experiment of the all fiber sensing system based on spectrum absorption theory. The main research contents s are as follows:(1)Based on molecule spectrum theory and experimental, the spectrum absorption characteristic of methane and carbon monoxide molecule in near infrared region is studied on detail. This played solid foundation for measurement wavelength selection, and effectively eliminated cross sensitivity.(2)In order to restrain the signal measurement component, which has no relationship with density, and improve the sensitivity of the measurement system, the paper make deep research on the gas sensing technology based on spectrum absorption theory.(3)Using the narrowband filter characteristics of fiber Bragg grating, differential absorption measurement system and harmonic measurement system is designed respectively.(4)Using FBG as an optical filter, all-fiber system measuring two research gases on line is designed. The optical sensing gas chamber is designed and made. In addition, the characteristic of light source and the detector is discussed, and coupling technologybetween light source with the fiber, and the fiber with the detector, as well as fiber with the gas chamber is studied.(5)Study on detection technology of the weak absorption signal, design the photoelectric detecting circuit with higher SNR.(6)Experimental research and analysis have been completed, which includes SLED spectrum characteristics, characteristic of detector, and absorption experiment of methane and carbon monoxide.