差分光学吸收在线测量有害气体研究

【作者】 徐理明；

【导师】 杨小丽；

【作者基本信息】 电子科技大学 ， 光学， 2010， 硕士

【摘要】 随着工业化进程加快,环境问题也逐渐引起人们的关注,其中空气中的气体污染给人们的健康带来较多的影响,检测环境污染气体成为需要。气体检测有多种方法,但是传统气体检测往往不能较好地适合生活环境场合,它们一般具有操作复杂、仪器笨重、有一定危害、不能实时测量等特点。本文使用光学吸收原理,对三种常见危害气体一氧化碳、甲烷和甲醛进行气体浓度测量设计,旨在设计出安全、可实时监测的小区域大气中污染气体测量仪。气体对光的吸收作用可以使用Lambert-Beer(朗伯-比尔)定律来描述。为了将此定律应用于气体检测中,必须要分析待测气体的光吸收特性。本文对三种气体一氧化碳、甲烷和甲醛进行了吸收光谱的波段分析和气体之间光谱对比分析,在中红外分别为三种气体选择了气体吸收峰作为气体检测的使用波长。在测量中直接应用Lambert-Beer(朗伯-比尔)定律是有诸多困难的,因为有多种误差的存在,差分光学吸收测量方法可用来消除这些误差。差分光学吸收测量方法有多种具体形式,文章对比分析了几种重要方法,结合设计需要,选择了本文改进的双波长单光路法作为测量原理,并选择LED光源配合滤光片使用来获得双波长光源。双波长单光路检测方法,一方面在气体吸收峰波长处探测气体对光的吸收强度,吸收的强度可以反映气体浓度;另一方面在吸收峰附近的参考波长处进行同样的测量,目的在于使用吸收峰波长处的探测光强除以参考波长处探测光强来消除光源波动、干扰气体和烟气颗粒等带来的影响。本文根据三种气体测量的使用波长,对LED光源、探测器、滤光片进行了选材,并使用ZEMAX软件进行了发射、接收等光路设计,对光路光能损耗率进行了计算。探测器探测光信号后要进行一些初始的信号处理,这部分主要是对探测到的微弱信号进行放大、滤波和对信号进行采样获得数字信号,文章进行了放大、滤波、峰值检波电路等设计。更多还原

【Abstract】 With the accelerated process of industrialization, environmental issues have been the focus of the people’s attention. One of the environmental issues, air pollution causes more and more impact on the people’s health, so the detection of environmental pollution gas becomes essential. There are several methods of gas detection, the traditional methods have the drawbacks, such as complicated operation, heavy equipment, some hazards, not real-time measurement. This thesis uses the optical absorption principle to do the gas concentration measurement design for three common harmful gases carbon monoxide, methane and formaldehyde, aiming to design a safe, convenient, real-time monitoring and detecting small regional atmospheric gas meter.The law of optical absorption principle can be described by Lambert-Beer law. In order to apply the law for the gas detection, the analysis of the gases’optical absorption properties is necessary. This thesis gives wave band analysis for the three gases carbon monoxide, methane and formaldehyde in the band of absorption spectra, and the comparative analysis for each other. Three gas absorption peaks for the gases in the mid-infrared are taken as their measurement waves. Direct use of Lambert-Beer law in gas concentration detection has many difficulties due to the existence of some kinds of errors. In this thesis, the differential optical absorption measurement method is used to design the structure of gas concentration measurement. Differential optical absorption measurement method has several specific forms. This thesis analyzes several important ways, and adopts a improved dual-wavelength single-beam method which is provided in this thesis. The LED together with the use of optical filter is selected to obtain dual-wavelength light sources. Dual-wavelength single-beam method on one hand detects the intensity of the light absorption at one of the gas absorption peaks, which can be used to calculate gas concentration, on the other hand implements the same measure at the reference wavelength near the absorption peak wavelength intending to use the quotient of the detected light intensity at the gas absorption peak wavelength and the detected light intensity at the gas reference wavelength to eliminate the errors caused by light intensity fluctuation of light source and affections of other gases and smoke particles. According to the use of three types of gas measurement wavelength, this thesis selects the LED light source, detector and filter, and uses ZEMAX optical design software to do the corresponding optical design such as transmitter and receiver. The loss rate of light path is calculated in this thesis. The detected light signal must be processed initially, which involve the weak signal amplification, filtering and the digital signal converting, so amplifier, filter, peak detection circuit etc are designed in this thesis.更多还原