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Research On Two Optical Paths Fiber Gas Sensor Based On Harmonic Detection

Posted on:2010-07-11Degree:MasterType:Thesis
Country:ChinaCandidate:Y P ChuFull Text:PDF
GTID:2178360302459152Subject:Optics
Abstract/Summary:PDF Full Text Request
Recently, the coal mine accidents in our country, especially gas exploding, happened frequently, which has endangered the miners'lives and the safety of the national properties. Air pollution has seriously affected people's health and life. For the bad gas like methane, carbon monoxide, sulfureted hydrogen, the safe and effective gas detection system is urgently needed. Fiber gas sensing is a high sensitivity developing gas detection technique. Gas 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. Thus, the basic principle of sensor's mathematical model is given.Second, spectral modulation techniques are applied into concentration detection because gas has very weak absorption in near-infrared region. The principles of wavelength modulation and harmonic detection are discussed detailedly. And the principle of lock in amplifier technique is given. Therefore, the weak signal can be picked up and amplified. The harmonic degree is chosen through numerical value simulation. Analyzed the measurement principles of wavelength modulation based on narrowband light source(DFBLD) and broad band(LED) light source. The mathematical model of harmonic detection is built up. And double optical path measurement scheme based harmonic detection is designed.Finally, the characteristics and influences on measurement of light source, gas cell, detector, optical path and electric signal detection system are analyzed. The theoretic former machine with double optical path based harmonic detection is designed which reduce the cost and lay the foundation for the practical use of gas measurement equipment. 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 the feasibility of the system and theoretic former machine.
Keywords/Search Tags:Near-infrared absorption, Wavelength modulation technique, Fiber Bragg grating, Piezoelectric ceramic, Lock in amplifier technique, Second harmonic measurement, Methane
PDF Full Text Request
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