【作者】 王喆；

【导师】 汪曣；

【作者基本信息】 天津大学 ， 生物医学工程， 2016， 硕士

【摘要】 氨气（NH₃）是我国大气污染物中一个重要的组成部分,精确测量其浓度具有非常重要的意义。可调谐二极管激光吸收光谱（TDLAS）技术利用单线光谱窄带吸收的特性,具有高灵敏度、强选择性、可避免其他无关成分干扰等优点,能够满足其他测量手段无法满足的实时在线快速准确测量需求,已逐渐成为一种重要的氨气浓度测量方法。本文在气体吸收的原理基础上,阐述了TDLAS技术理论,说明了波长调制技术的优点,重点介绍了TDLAS技术中采用的波长调制和谐波探测理论,进而给出TDLAS技术对氨气浓度检测的依据和原理。依据TDLAS系统的基本原理,完成了对系统各个模块的建模仿真,以用于后续分析,并搭建了TDLAS氨气浓度检测实验系统。文中阐述了氨气吸收峰选取的方法,给出了系统中各模块的选取,对激光器调谐参数和锁相放大器参数进行了优化,完成了对氨气浓度的检测,验证了系统检测的性能。TDLAS技术用于痕量氨气浓度检测时,气体吸收信号信噪比较低,因此如何去除系统噪声一直是研究的热点。本文分析了连续截断信号和构造hankel矩阵两种不同方法下,奇异值分解（Singular Value Decomposition）对TDLAS系统检测氨气浓度的理论意义,并应用仿真建模系统及搭建的TDLAS氨气浓度检测系统进行分析。将二次谐波信号分别用两种方法进行矩阵化排列和奇异值分解,选取适当阈值将部分奇异值置零并重构矩阵,得到了这两种方法对基线纠漂和去噪的不同效果。实验证明,奇异值分解方法不需要加入额外的系统部件、不需要通入零气进行背景扣除,就能够快速有效地去除TDLAS系统噪声,而构造hankel矩阵的方法适用于去除高频噪声,构造连续截断信号矩阵的方法适用于进行基线纠漂。将该方法应用于实际TDLAS系统氨气检测时的二次谐波,系统噪声去除率达80%。更多还原

【Abstract】 Ammonia is a major part of atmospheric pollutants,accurate measurement of the ammonia concentration is very important.TDLAS（Tunable Diode Laser Absorption Spectroscopy）is based on single-line narrowband spectrum absorption characteristics.It has many advantages such as high sensitivity,high selectivity,to avoid interference to other unrelated components.TDLAS can meet real-time online fast and accurate measurement needs,which other measurements can not.It has gradually become an important measurement of ammonia concentration.Based on the principles of gas absorption,this paper describes the basic theory of TDLAS technology.It analyzes the advantages of wavelength modulation technology.And highlights the wavelength modulation and harmonic detection theory that TDLAS technique employed,gives evidence and principles of ammonia concentration measurement by TDLAS.For subsequent analysis,this paper has completed the various modules of the system modeling and simulation according to the basic principle TDLAS system.We have established TDLAS ammonia concentration detection experimental system and introduced ammonia absorption peaks and selections of every part in system.In this paper,the laser tuning parameters and lock-in amplifier parameters are optimized,and has completed the detection of ammonia concentration.Detection of gas concentration by TDLAS is affected by baseline drift and high-frequency noise.Therefore,how to remove the systematic noises has been a hot spot.This paper analyzes the significance of singular value decomposition（SVD）in TDLAS detection system with two different methods of constructing a matrix,and discusses the differences of processing results for different noises by using simulation modeling systems and TDLAS ammonia concentration detection system.The second harmonic signal is arranged in a matrix and decomposed.We select the appropriate threshold and put those singular values smaller than the threshold into zero,then reconstruct the matrix.Experiments show that SVD method does not require additional system components or pass into the zero gas to subtract background.This method is able to remove noises of TDLAS system quickly and effectively.We found that the method of constructing a hankel matrix is suitable for removing high-frequency noise.While,the method of constructing a continuous-cutoff-signal matrix is suitable for removing baseline drift.For example,we set up a TDLAS system to measure the concentration of NH₃,the noise removal rate of second harmonic curve up to 80% after this method.更多还原