Study On C₂h₄ Density Detecting System Based On Spectrum Absorption

Ethylene is the basic stuff and the core material in the petroleum chemical industry. Ethylene exists by nature on the chemical term. It is prone to explode and burn. It is essential to detect the ethylene density in the air for ensuring the security.The optical fiber sensor, compared with the traditional sensor, has the outstanding advantagement:high sensitivity, resistance against the electromagnetic disturbing; The transmission loss is low; wide measuring range; high accuracy; long operating life; good stability. Thanks to the superiorities, the fiber sensor has been developed greatly.The subject of the essay is to design a optical fiber sensor system by the ethylene. The basic theory is that using spectral absorption fiber sensor tech,Harmonic detection and Labview detect the ethylene density. The principle is the lab-beer law. As the emerging light is weak, choosing DFB-LD as the optical source, the Harmonic detection tech and phase-lock amplifier detect the weak signal.The main work of this essay:1,Explain the theory of the spectral absorption on measuring the gas density; analyze the Harmonic detection theory and how to put the theory into practice.2,Confirm the ethylene absorption range/interval and absorption peak 1626nm; select the wave 1626 as the absorption point, which is the precondition to confirm the light source.3,Choose the narrow spectral line and good stability DFBLD as the light source in the system, using the laser control to complete the wave modulation and temperature control; keep the light wave at the 1626nm, matching the gas absorption peak, promote the light stability and accuracy.4,Adopt the long optical path to enhance the optical path, making gas in the write room reflected by the gas, thus strengthening the gas to absorb the optical path, raising the sensitivity detection.5,Design the whole system on the measuring the ethylene detection; Introduce the every section and process of this system.6,Make use of phase-lock amplifier SR830 to find the weak signal and illustrate the amplifier structure and explain application in detail. 7,Give the Labview characters account for how to use the Labview and how to adopt and deal with the data when meeting the signal problems.8,Draw a conclusion about the relation between semi-conducer laser output-wavelength and the temperature, relation between the wavelength and drive curr ent.9,Discover the relation between the ethylene density and detection signal; Draw a line and derivate the function of the density.The system merits lie in high sensitivity, good stability. Meanwhile the system can apply in the high temperature poisonous and harmful condition. Furthermore, the system can be used on measuring other gas density. The system has broad application prospect and development opportunities.