近红外光谱吸收式气体检测系统的研究

发布时间：2018-01-11 06:13

本文关键词：近红外光谱吸收式气体检测系统的研究　出处：《吉林大学》2016年博士论文　论文类型：学位论文

【摘要】：近年来,我国安全生产问题和环境问题十分严峻。一方面,煤矿瓦斯爆炸、危险气体泄漏等安全事故频发,给国家造成了重大的经济损失和恶劣的社会影响。另一方面,大气中温室气体浓度的不断升高也带来了一系列的环境问题。因此,先进的气体传感器研发工作十分重要。基于红外吸收光谱原理进行气体检测是目前国内外较为先进的方法。与传统的化学类传感器相比,其具有检测灵敏度高、响应速度快、选择性好、检测范围大、稳定性好等优点。红外气体传感器还具有非接触性测量和寿命长的特点,非常适用于煤矿、工业控制及大气监测等领域。可调谐半导体激光吸收光谱技术是一种高精度红外气体检测的方法。该技术利用波长可以调谐的二极管激光器作为光源,通过改变激光器的温度和电流使得激光器中心波长反复扫过被测气体的吸收峰。由此可获得高分辨率的气体吸收信号,以达到对气体定性、定量检测的目的。与可调谐半导体激光吸收光谱技术相结合,波长调制光谱技术通过对激光器进行高频调制,并提取气体吸收信号的谐波波形,极大地降低了系统中的固有噪声,进一步提高了检测灵敏度。本文采用可调谐半导体激光吸收光谱技术与波长调制光谱技术相结合的方法,设计并制作了以近红外分布反馈式激光器为光源的气体检测系统。首先,以红外吸收光谱理论为基础,针对本论文所设计的检测系统进行了理论分析。通过对系统中检测流程和数据处理的逐步推导,将激光器驱动与调制、光电转换、谐波信号、气体浓度等相关参数进行关联运算,验证了二次谐波信号与气体浓度的相关性。并使用MATLAB软件进行了系统仿真,为气体检测实验提供参考依据。其次,根据系统中使用的激光器的具体驱动特性,设计并制作了激光器温度控制电路和电流驱动调制电路,使其输出光谱满足波长调制的要求,这是本文的重点内容。基于模拟PID算法,对温度补偿网络电路进行了元件配置和参数优化。激光器在温度控制电路的恒温控制下,输出光谱稳定,长时间工作时中心波长不漂移。在室温环境下激光器长时间工作的温度波动在±0.02℃范围以内。研制了激光器电流驱动调制电路,通过低频锯齿波的电流驱动,可以使激光器波长周期性变化而反复扫过气体吸收峰。同时,叠加高频正弦波对激光器进行调制,用于谐波提取。另外,为提高激光器温度控制的稳定性以及降低系统噪声,研制了低纹波线性稳压电源作为系统电源,其纹波干扰远小于常规的开关电源。再次,针对光源系统输出的激光信号,研制了用于检测和处理气体吸收信号的检测系统。检测系统分为差分光路系统、透射型光纤气室、光电转换电路和数字式正交锁相放大器几部分,是本文的又一重点内容。差分光路对单光源进行分光处理,两路信号的差分处理可以有效地减小光源噪声的影响。以光纤准直器为核心光学器件,设计了结构稳定、使用光纤进行通信的透射型气室。使用高性能的In Ga As光电二极管制作了光电转换电路,将气体吸收信号与参考信号进行光电转换,通过差分电路得到的差分信号包含了气体浓度信息。设计并制作了数字正交锁相放大器,将用于谐波提取的相敏检波过程通过软件程序完成。在对谐波提取算法进行仿真分析的基础上,通过气体实验成功提取了谐波信号,并对谐波提取的稳定性进行了测试,从实验角度再次验证了谐波信号与气体浓度的相关性。最后,通过甲烷和一氧化碳的气体检测实验,对检测系统进行了性能测试实验。使用动态配气方式,针对系统检测下限、重复性、稳定性、响应时间和示值误差等性能指标进行了相关实验。通过阿伦方差进行数据分析,系统的甲烷检测下限约为29 ppm,一氧化碳检测下限约为148 ppm。实验结果表明,检测系统具有良好的检测灵敏度和稳定性,同时该检测系统还具有集成度高、成本低等优点,通过更换不同波长的激光器,还可以对其它气体进行检测。
[Abstract]:In recent years, production safety and environmental problems is very serious in China. On the one hand, the coal mine gas explosion, dangerous gas leakage safety accidents, resulting in significant economic losses and bad social impact to the country. On the other hand, atmospheric concentrations of greenhouse gases continue to rise has also brought a series of environmental problems. Therefore, research and development of advanced gas sensor is very important. The infrared absorption spectrum principle of gas detection methods at home and abroad is relatively advanced. Compared with chemical sensors based on the traditional, it has high sensitivity, fast response, good selectivity, wide detection range, good stability of infrared gas sensor has the characteristics. Non contact measurement and long service life, is suitable for the coal mine, the field of industrial control and monitoring. Tunable diode laser absorption spectroscopy technology is a kind of high precision The method of infrared gas detection. The technology uses a diode laser wavelength can be tuned by changing the laser as the light source, the temperature and current makes the laser center wavelength repeatedly swept the absorption peak of the measured gas. The gas absorption signal to obtain high resolution, in order to achieve the purpose of gas qualitative, quantitative detection with tunable. Semiconductor laser absorption spectroscopy combined with wavelength modulation spectroscopy by high frequency modulation of the laser, and the extraction of harmonic wave gas absorption signal, which greatly reduces the system's inherent noise, further improve the detection sensitivity. This paper uses the method of combining tunable diode laser absorption spectroscopy and wavelength modulation spectroscopy. The design and fabrication of the near infrared distributed feedback laser gas detection system. Firstly, the infrared absorption spectrum of Science On the basis of the detection system designed in this paper is analyzed. Based on the process and data processing are gradually detection system, the laser drive and modulation, photoelectric conversion, harmonic signal, gas concentration and other related parameters related operations, to verify the two harmonic signal and the gas concentration and correlation. System simulation was carried out using MATLAB software, to provide reference for gas detection experiments. Secondly, according to the specific characteristics of the laser drive system using the laser temperature control circuit and the drive current modulation circuit design and make it meet the requirements of the output spectrum of wavelength modulation, which is the main content of this paper. The simulation algorithm based on PID the optimization and configuration parameters, components of temperature compensation circuit. Laser in temperature control circuit under the control of the output spectrum is stable, long time. When the central wavelength drift. The temperature fluctuation work in room temperature laser long time is within the range of - 0.02 DEG C. Current drive laser modulation circuit is developed, driven by the current low frequency sawtooth wave, which can make the laser wavelength periodic changes repeatedly sweep gas absorption. At the same time, the high frequency modulation of sine wave superposition the laser used for harmonic extraction. In addition, in order to improve the stability of laser temperature control and reduce system noise, developed a low ripple linear regulated power supply system as power supply, the ripple interference is far less than the conventional switching power supply. Once again, the laser signal source output system, for detecting and processing gas absorption signal detection system is developed. The detection system is divided into differential optical transmission system, optical fiber gas chamber, a photoelectric conversion circuit and digital quadrature lock-in amplifier is the part. Another key difference of single light source. Optical processing optical signals, differential treatment can effectively reduce the noise of light source. Optical fiber collimator as the core to design the optical device, stable structure, transmission type gas chamber using optical fiber communication. In Ga As photodiode with high performance the production of the photoelectric conversion circuit, gas absorption signal and the reference signal of the photoelectric conversion, the differential circuit of differential signal contains gas concentration information. Making the digital orthogonal lock-in amplifier is designed and will be used for phase sensitive detection of harmonic detection is accomplished by means of software. In the simulation based on harmonic extraction algorithm the analysis on the experimental gas through the successful extraction of harmonic signals, and the stability of harmonic extraction were tested and verified again from the point of view of experimental harmonic signal and gas concentration The correlation. Finally, through the experiment of methane gas and carbon monoxide detection, the performance test of detection system. Using the dynamic gas mixing system, aiming at the detection limit, repeatability, stability, response time and error performance of the experiment. The data were analyzed with Allen variance, methane detection limit the system is about 29 ppm, the detection limit of carbon monoxide is about 148 ppm.. The experimental results show that the detection system has good sensitivity and stability at the same time, the detection system also has the advantages of high integration, low cost and other advantages, through the replacement of lasers of different wavelengths, but also can be used to detect other gases.

【学位授予单位】：吉林大学
【学位级别】：博士
【学位授予年份】：2016
【分类号】：TN247

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