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Study on C2H4 Density Detecting System Based on Spectrum Absorption

Author: YangXueLing
Tutor: CaoYeWen
School: Shandong University
Course: Communication and Information System
Keywords: Optical fiber gas sensor Harmonic Detection Lock-in amplifier Labview
CLC: TP274
Type: Master's thesis
Year: 2010
Downloads: 145
Quote: 0
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Abstract


Ethylene is one of the basic petrochemical raw materials, but also the core of the petrochemical industry, the chemical properties of ethylene active, is flammable and explosive gases, the concentration of ethylene in the detection of air and equipment is a necessary condition to ensure safety. Fiber optic sensors are compared with conventional sensors with outstanding advantages: high sensitivity; resistance to electromagnetic interference; low transmission loss, wide measuring range, high precision;, long life, stable work. It is these advantages contributed greatly to the development of optical fiber sensing technology. To ethylene gas for the study objectives, the design of a fiber-optic gas sensing system, the basic theory of harmonic detection technology, spectral absorption optical fiber sensing technology and LabVIEW, the basic principle is to detect the concentration of ethylene gas Lambert-Beer's law, but outgoing light intensity is weaker, selected long-path absorption DFB LD (distributed feedback semiconductor laser Distributed Feedback Laser Diode) light source, the use of harmonic detection and lock-in amplifier to detect weak signals. The main work done in this thesis elaborated the basic principles of the spectral absorption measurement of gas concentration, from the theoretical analysis of the principle and method of harmonic detection determined the absorption range of ethylene absorption peak, and select the absorption peak wavelength 1626nm which is determined as the point of absorption, the premise of the light source. 3 Select a narrow spectral line, the good stability DFBLD as the light source of the system, and with the completion of the laser controller of the wavelength modulation of the light source and temperature control, at 1626nm, and the gas absorption peak phase matching, to improve the light emission wavelength of the light source stability and accuracy. 4 absorbs the gas chamber with a long optical path absorption (Write pool) to increase the optical path, so that the gas in the Write an indoor multiple reflections through the gas, strengthen the optical path of the gas absorption, to improve the measurement sensitivity. Designed for measuring the concentration of ethylene overall system, and made a basic introduction to the various parts of the system and work processes. 6 using a lock-in amplifier SR830 weak signal detection, described in detail the principles and structure of the lock-in amplifier. Preliminary paper describes the features of LabVIEW software, LabVIEW virtual instrument with the signal processing, data acquisition and processing, graphical programming. The article also on the performance of the laser test, obtained semiconductor laser output wavelength and temperature dependence of the output wavelength drive current relationship. 9 the relationship between the ethylene concentration in the measurement signal is obtained by experiment. Draw the experimental curve derived function of the concentration of the calculation. The system has the advantages of high sensitivity, good stability in the harsh environment of high temperature, toxic and hazardous applications, can be improved to measure the concentrations of other gases, and has broad application prospects and development space.

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