基于TDLAS技术的微弱信号处理电路设计

发布时间：2019-02-15 04:52

【摘要】：近年来,气体污染的现象日益严重,对特定环境下的有害气体浓度的检测也受到越来越多的关注。以TDLAS(Tunable Diode Laser Absorption Spectroscopy)这一可调谐二极管激光吸收光谱检测技术为代表用于检测气体浓度的方法已经成为工业在线检测气体浓度的首选方法之一。本论文针对TDLAS气体检测系统中微弱信号的处理设计了一款可以实现倍频移相的锁相放大器,用来提取被测气体的二次谐波信号。本文首先设计了检测系统的整体框图,主要包括光电探测器、光电转换电路、锁相放大电路、低通滤波电路、A/D转换电路以及电源电路。其中,在TDLAS检测系统中设计的锁相放大部分的电路主要包括:前置放大、带通滤波、TTL电平转换、倍频移相、相敏检波、低通滤波、双相限幅电路等。根据锁相环频率合成器的基本原理,该锁相模块设计的重点是倍频移相电路的设计,主要是利用了74HC4046以及74HCT161这两个芯片实现锁相环的倍频移相控制,可根据实际情况自行设置相移。在本文中搭建的实验环境选择的是以氨气配置不同浓度的空气来检测空气中O2的浓度,已知某一浓度的气体来检测二次谐波的正确性。首先对电路板进行测试,并且通过仿真实验来验证所设计的锁相放大器各个部分的波形图以及整体电路功能仿真波形图,在没有问题的情况下,连接上位机软件,通过注入已知浓度的气体来验证锁相放大器提取的二次谐波信号是否正确,通过实验结果表明TDLAS检测技术使用二次谐波检测气体浓度的可行性和准确性。
[Abstract]:In recent years, the phenomenon of gas pollution is becoming more and more serious, and the detection of harmful gas concentration in specific environment has attracted more and more attention. TDLAS (Tunable Diode Laser Absorption Spectroscopy), a tunable diode laser absorption spectrum technique, has become one of the preferred methods for detecting gas concentration on line. In this paper, a phase-locked amplifier is designed for the processing of weak signals in TDLAS gas detection system, which can be used to extract the second harmonic signal of measured gas. In this paper, the whole block diagram of the detection system is designed, including photodetector, photoelectric conversion circuit, phase-locked amplifier circuit, low-pass filter circuit, A / D conversion circuit and power supply circuit. Most of the circuits designed in TDLAS detection system include preamplifier, bandpass filter, TTL level conversion, phase doubling, phase sensitive detection, low pass filter, biphase limiting circuit and so on. According to the basic principle of PLL frequency synthesizer, the emphasis of the design of PLL module is the design of frequency-doubling phase-shift circuit. The two chips, 74HC4046 and 74HCT161, are used to realize the phase-doubling control of PLL. Can set the phase shift according to the actual situation. In this paper, the experimental environment is designed to detect the concentration of O2 in the air with different concentration of ammonia, and the correctness of detecting the second harmonic is determined by a certain concentration of gas. First of all, the circuit board is tested, and the waveform diagram of each part of the phase-locked amplifier and the whole circuit function simulation waveform are verified by the simulation experiment. In the case of no problem, the PC software is connected. The second harmonic signal extracted by the phase-locked amplifier is proved to be correct by injecting gas with known concentration. The experimental results show the feasibility and accuracy of using the second harmonic detection technique to detect the gas concentration in TDLAS.
【学位授予单位】：西安电子科技大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：TN247;TN911.7;TN722

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