| As in recent years hydrogen sulfide(H2S) gas has leaked out frequently in production and daily life, the safety issues on H2S gas has gradually become the focus of attention, which made the requirement to develop a on-line real-time, fast, efficient H2S gas sensing with high sensitivity, and low detection limit an ever more urgent one. Although a traditional H2S gas sensor can achieve a low detection limit, it is vulnerable to be influenced by other gas via cross-sensitivity, besides it has other disadvantages,including relatively slow response, low reusable rate, short life span and difficulty to achieve on-line continuous monitoring. Because the optical fiber is small and light, also easy to bend, resistable to electromagnetic interference and radiation performance.It gets scholars'more and more attention in recent years.An optical fiber H2S gas sensor based on NIR absorption spectrum has been proposed in this paper.It analysised the selecting absorption theory of near infrared spectral, using DFBLD light source and Lambert-Beer's law. H2S gas detection use harmonic detection technology. The single isolated rotational absorption lineυ1 +υ2+υ3 around 1578nm is chosen as the center absorption line of H2S gas, which has an absorption intensity of approximately of 1.3×10 -22( cm molecule). To eliminate the adverse influence originating from the fluctuation of the source power, a differential system which compares the signal with the reference light is adopted.Through to theoretical analysis of H2S gas absorption spectrum the calculation result, under normal temperature atmospheric pressure, shows that the H2S in center frequency of gas in the absorption coefficient is about 1.5×10-2 cm ? 1 ?atm?1, the widening mechanism of spectral lines is mainly collisional broadening, H2S absorption line-shape can choose Lorentz or Voigt.In paper, H2S gas detection adopts lock-in amplifier technology by gas concentration of the harmonic signals caused. First harmonic as error feedback signal, will the wavelength of the light source of accurate absorption peaks on gas, the second harmonic signals are used to test the concentration of the gas, using the second harmonic and a harmonic of the ratio of the light to eliminate because not stability and change and a test error, improve the detection of the reliability of the system.Due to a weak signal, there are many factors affect the measurement precision. So before the actual development, it best can computer simulat, to find out all kinds of parameters on the influence of the measurement precision. At last, the simulation system for H2S gas absorption is established, to validate the system on the feasibility of gas detection. System is calibrated through data measurement and fitting processing. There is some reference value for actual detection system. |
PDF Full Text Request