Study On Fiber Optic Methane Sensing System

Methane is inflammable and explosion hazard gas as the basis of mash gas, firedamp and rock gas. So exact measure methane in the environment can avoid and prevent catastrophic failure and ensure public safety.Gasmetry technique based on spectrum absorption has high measure sensitivity and resolving ability, and an important technique in the field of environmental monitoring and industry gas process control. But traditional absorption spectral analysis can only collect specimen in the open or practice work environment in usual, and then make spectral analysis in laboratory environment. It has definite limitations in the practical application, especially in the field of environmental monitoring and industry gas process control. The method can not satisfy the request of real time and online continues monitoring. But the fiber gas sensor is safe in nature, has small influence by environment, is easy to compose network and is suitable for remote transmission. So the traditional gas absorption spectral analysis technique and fiber optic sensing technique combines to the new gas-sensing technology, which receives more and more recognition in the field of industry, military and scientific research.The thesis uses the Near-Infrared spectrum absorption fiber optic sensing technique. And the main component of mine gas methane is used as a research example. After analyzing the theory of near-infrared selective absorption of gas, we describe the academic based of the measurement of the gas by absorption theory. The test method of the system is determined by studying on weak spectrum absorption test method. The fiber optic methane sensing system based on DFB laser is designed and completed. This paper totally includes six chapters. The contents of the paper are as follows:The first chapter introduces the classification of fiber optic sensing technique, current research state of spectrum absorption fiber optic sensing technique and analyzes the possibility and necessity of studying on the fiber optic methane sensing system.The second chapter expounds the theory of near-infrared selective absorption of gas, analyzes the characters of gas absorption spectral line and selects the absorption spectral line of methane in 1330nm after synthesizes various aspects factor. We analyzes two basal weak spectrum absorption test methods, which includes difference absorption method and frequency modulation harmonic detection method. The system selects the high precision harmonic detection method with narrowband light source and creates the math model of harmonic detection. Then we totally design the system on the basis of theory analysis.