全光式石英增强光声光谱系统光纤法珀解调技术研究

发布时间：2018-03-17 00:34

本文选题：痕量气体检测　切入点：QEPAS　出处：《重庆大学》2014年硕士论文　论文类型：学位论文

【摘要】：痕量气体检测技术已经在空气污染监测、工业生产、医学诊断等领域发挥着重要的角色，，其中石英增强光声光谱技术（Quartz Enhanced Photoacoustic Spectroscopy,QEPAS）是一种完全无背景的气体检测技术，因其具有体积小、灵敏度高、响应速度快以及适合实时在线测量等优点而被广泛地应用。针对一些特殊情况，例如高温、高湿度、强电磁场干扰环境中以及易燃、易爆和有毒有害气体的检测，目前的检测技术还是存在一些局限性。本文利用光纤法珀振动传感技术获取与气体浓度相关的石英音叉振动信号替代了传统方法中获取音叉压电信号，同时采用法珀传感器工作点稳定技术，进一步提高QEPAS系统的解调精度和稳定性。论文从石英增强光声光谱系统的原理出发，详细地推导了气体光声理论和音叉的振动幅值与气体的浓度关系。理论分析了波长调制和谐波检测技术的必要性。采用光纤法珀传感器拾取音叉的振动信号，从多光束干涉公式详细地分析了法珀传感器输出信号与音叉振动幅值的关系，并通过仿真和实验分析了工作点漂移对解调结果的严重影响，结合波长补偿技术使得工作点稳定在正交相位点上，以获得更好的解调结果。石英增强光声光谱光纤法珀解调系统设计主要包括光源光纤激光器的设计和工作点反馈控制设计。论文中详细分析了掺铒光纤放大原理，设计了基于可调谐FP滤波器的光纤激光器，得到其功率可达10mW、调谐范围为1525nm~1565nm以及线宽约为0.00051nm。基于LabVIEW软硬件平台，设计了反馈式光纤法珀传感控制模块。由采集卡获得传感器的输出信号并由软件对其进行滤波和取直流处理，采用得到的直流电压与静态工作点电压之差作为误差反馈信号，利用数字PID技术将工作点锁定在正交相位点上，提高光纤法珀传感器的稳定性，从而提高了光声信号探测的准确性。为了验证基于法珀传感的石英增强光声光谱系统的可行性，实验中选择水蒸汽作为测试气体样本，在开放环境中对水汽进行测试实验。由实验结果计算得到其归一化等效噪声吸收系数为1.81×10-7cm-1W/Hz1/2。与传统的QEPAS气体探测系统相比较，该方法的探测灵敏度提高了4倍。该系统具有成本低和探测效率高、抗电磁干扰及防燃防爆能力和适合长距离在线检测等优点。
[Abstract]:Trace gas detection technology has played an important role in air pollution monitoring, industrial production, medical diagnosis and other fields. Quartz enhanced photoacoustic spectroscopy (Quartz Enhanced Photoacoustic SpectroscopyQEPAS) is a completely groundless gas detection technology. It is widely used because of its small size, high sensitivity, high response speed and suitable for real time on-line measurement. It can be used in some special cases, such as high temperature, high humidity, strong electromagnetic field interference and flammability. Detection of explosive and toxic gases, At present, there are still some limitations in the detection technology. In this paper, we use the fiber Fabry-Perot vibration sensing technology to obtain the quartz tuning fork vibration signal which is related to the gas concentration instead of the traditional method to obtain the tuning fork piezoelectric signal. At the same time, the demodulation accuracy and stability of QEPAS system are further improved by using the technology of working point stabilization of Fabry-Perot sensor. Based on the principle of quartz enhanced photoacoustic spectroscopy system, The relationship between the vibration amplitude of the tuning fork and the concentration of the gas is derived in detail. The necessity of wavelength modulation and harmonic detection is analyzed theoretically. The vibration signal of the tuning fork is picked up by the fiber optic Fabry-Perot sensor. The relationship between the output signal of the Fabry-Perot sensor and the amplitude of the tuning fork vibration is analyzed in detail from the multi-beam interference formula, and the serious influence of the working point drift on the demodulation result is analyzed by simulation and experiment. Combined with wavelength compensation technology, the working point is stabilized on the orthogonal phase point to obtain better demodulation results. The design of quartz enhanced photoacoustic spectrum fiber Fabry-Perot demodulation system mainly includes the design of light source fiber laser and the design of operating point feedback control. A fiber laser based on tunable FP filter is designed. Its power is up to 10mW, tuning range is 1525nm / 1565nm and linewidth is about 0.00051nm.Based on LabVIEW software and hardware platform, The feedback fiber Fabry-Perot sensor control module is designed. The output signal of the sensor is obtained by the acquisition card and filtered and processed by the software. The difference between the obtained DC voltage and the static working point voltage is used as the error feedback signal. In order to improve the stability of optical fiber Fabry-Perot sensor and improve the accuracy of photoacoustic signal detection, digital PID technology is used to lock the working point on the orthogonal phase point. In order to verify the feasibility of quartz enhanced photoacoustic spectroscopy system based on Fabry-Perot sensor, water vapor was selected as the test gas sample in the experiment. The normalized equivalent noise absorption coefficient is 1.81 脳 10 ~ (-7) cm ~ (-1) W / H ~ (-1 / 1 / 2), which is compared with the conventional QEPAS gas detection system. The system has the advantages of low cost, high detection efficiency, anti-electromagnetic interference and flame-proof capability and suitable for long distance on-line detection.
【学位授予单位】：重庆大学
【学位级别】：硕士
【学位授予年份】：2014
【分类号】：O657.3;TP212

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