基于TDLAS技术甲烷检测的温度影响及补偿研究

发布时间：2018-04-23 03:09

本文选题：甲烷气体 + 温度影响　；参考：《山东大学》2017年硕士论文

【摘要】：气体检测技术应用于多个领域。目前的气体检测技术有多种手段,激光光谱方法由于其精度与实时性等优点成为发展的方向。然而,当被测气体的温度发生大范围改变时,被测气体的物理性质也随之发生改变,导致激光光谱检测方法的测量结果不准确。针对这个问题,本文提出了一种依赖二次谐波信号并且不需测量被测气体实际温度的温度补偿算法。本文分别通过理论分析、算法建模以及验证测试的方法进行课题研究。首先建模分析温度对甲烷检测的影响。建立三种吸收线型的模型,并比较选择适合课题研究内容的吸收线型为Lorenz Profile。然后,分别从气体分子数密度、线宽、线强三个方面分析温度对吸收系数产生的影响,以及谐波检测中温度对二次谐波信号产生的影响。当温度由-30摄氏度变化到120摄氏度,气体分子数密度数值减小了 38.6%,线强减小了 45%,线宽减小了 29.7%,吸收系数减小了 51.7%,二次谐波信号中心频率点的数值减小了 51.6%。目前温度影响的解决办法一般采取经验公式或者理论公式方法进行补偿校正,但前提是获取到被测气体的温度。或者,同时对两条吸收谱线进行测试,同时获得被测气体温度与浓度。本文提出一种补偿温度影响的新方法。二次谐波信号包含了被测气体的浓度信息,选取二次谐波中两个频率点对应数据的差值进行浓度的反演计算,采取这种方法,计算结果对温度的依赖性比较小。在算法模型中,以调制幅度为1为例,当温度由-30摄氏度变化到120摄氏度时,用二次谐波信号中心频率点的数值进行浓度反演计算时,相对误差可达到51.6%;采取本文提出的新方法时,最大值最小值偏差为12.7%,很大程度上减小了测量结果对于温度的依赖性。将算法进行验证测试,采集不同温度下相同浓度甲烷气体的浓度数据,测量结果与理论模型的分析结果基本一致。在这些数据的基础上做补偿算法的验证,使温度对测量结果的影响减小了 50%,有一定的改善效果。但理论结果与实验结果仍然存在一定的差距,分析是激光器性能以及环境噪声的原因。
[Abstract]:Gas detection technology is applied in many fields. At present, there are many methods for gas detection, and laser spectrum method has become the direction of development because of its accuracy and real-time. However, when the temperature of the gas is changed in a wide range, the physical properties of the gas are also changed, which leads to the inaccurate measurement results of the laser spectrum detection method. To solve this problem, this paper presents a temperature compensation algorithm which depends on the second harmonic signal and does not need to measure the actual temperature of the gas being measured. In this paper, the methods of theoretical analysis, algorithm modeling and verification test are studied. Firstly, the influence of temperature on methane detection is analyzed. Three kinds of absorption line models are established, and Lorenz profile is chosen as the suitable absorption line. Then, the influence of temperature on absorption coefficient is analyzed from three aspects of gas molecular number density, line width and line strength, as well as the influence of temperature on second harmonic signal in harmonic detection. When the temperature changes from -30 degrees Celsius to 120 degrees Celsius, the gas molecular number density value decreases by 38.6, the line strength decreases by 45, the linewidth decreases by 29.7m, the absorption coefficient decreases by 51.7 percent, and the value of the center frequency of the second harmonic signal decreases by 51.6. At present, the solutions to the influence of temperature are usually compensated by empirical formula or theoretical formula, but only if the temperature of the measured gas is obtained. Alternatively, two absorption lines are measured at the same time, and the gas temperature and concentration are obtained simultaneously. A new method for compensating the influence of temperature is presented in this paper. The second harmonic signal contains the concentration information of the gas to be measured. The difference between the two frequency points in the second harmonic wave is selected to carry out the inversion calculation of the concentration. By adopting this method, the temperature dependence of the calculation results is relatively small. In the algorithm model, taking the modulation amplitude of 1 as an example, when the temperature changes from -30 degrees Celsius to 120 degrees Celsius, the concentration inversion calculation is carried out with the numerical value of the center frequency point of the second harmonic signal. The relative error can reach 51.6, and the maximum and minimum deviation is 12.7, which greatly reduces the dependence of measurement results on temperature. The algorithm is validated and tested, and the data of methane concentration of the same concentration at different temperatures are collected. The measured results are in good agreement with the analytical results of the theoretical model. On the basis of these data, the effect of temperature on the measurement results is reduced by 50%, and the effect is improved to a certain extent. However, there is still a gap between the theoretical results and the experimental results. The analysis is the reason of the laser performance and ambient noise.
【学位授予单位】：山东大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：O433;TN24

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