Research On Methane Detection Based On The Principle Of Near-Infrared Absorption

Methane is a flammable and explosive gas. It is the main component of mine gas and many liquid fuels. So it is very important to detecting methane concentration in mine safety and environment inspecting areas. Fiber gas sensing is a high sensitivity gas detection technique. Methane concentration measurement is the paper's purpose. Fiber methane gas sensing technique is studied based on the principle of near infrared absorption. The main contents are as follows:First, the research actualities and progress directions of fiber gas sensor in nation and abroad are discussed. The influence factors and key techniques of fiber gas sensor are analyzed. The basic principle of gas absorption measurement is given through the analysis of molecule spectrum theory. The near-infrared absorption spectrum of methane is chosen. And its absorption characteristic is analyzed. Thus, the basic principle of sensor's mathematical model is given.Secondly, spectral modulation techniques are applied into concentration detection because methane has very weak absorption in near-infrared region. The principles of wavelength modulation and harmonic detection are discussed detailedly. The harmonic degree is chosen through numerical value simulation. The mathematical model of harmonic detection is built up. And double optical path measurement scheme based harmonic detection is designed. The principles of intensity modulation and difference absorption are discussed. The scheme of fiber grating and difference absorption detection is designed. And the principle of lock in amplifier technique is given. Therefore, the weak signal can be picked up and amplified.Finally, the characteristics and influences on measurement of light source, gas cell, detector, optical path and electric signal detection system are analyzed. The grin lens gas cell is designed which can reduce interference signal. The source spectrum characteristics are tested. The experiments consisting of methane absorption spectrum, the relationship between detection signal and methane concentration, repeatability test and stability test are studied. The experiments results have proved that the system is feasible.