基于光谱吸收式的光纤甲烷气体传感系统

【作者】 周游；

【导师】 刘永智；

【作者基本信息】 电子科技大学 ， 光学工程， 2008， 硕士

【摘要】 光纤气体传感技术是一项正在发展中的新型测试技术,在矿井、油田以及电力系统安全保护、环境监测和医学等领域具有广阔的应用前景。光纤气体传感器以光作为被测量的信号载体,自身独立性好,可以在各种复杂环境下使用。光信号传输距离长,且易于组网,可满足长距离、多功能、智能化的要求。本文以矿井瓦斯的主要成分甲烷为监测对象,研究基于光谱吸收的全光纤气体监测系统。该系统具有对测量信号有较高的响应速度、测量灵敏度高、动态范围大、防燃防爆、防电磁干扰、不易中毒等优点。在实际测量中,传感头可以放置在人和仪器不易进入的易燃易爆、有毒等恶劣环境中,实现信号在线遥测,从而达到实时监测甲烷浓度、及时报警,避免瓦斯爆炸事故发生的目的。通过对气体近红外选择性吸收的理论分析,给出了气体吸收测量的理论依据。根据甲烷气体的吸收谱线,找出适合普通石英光纤进行较长距离低损耗传输的光谱特性。采用分布反馈式半导体激光器(DFB LD)作为光源,通过光源调制实现气体浓度的谐波检测,利用二次谐波与一次谐波的比值来消除由光源的不稳定等因素所引起的检测误差。建立了谐波检测的数学模型。文中论述了近红外波段激发光源的光强稳定技术; DFB LD和气体吸收峰中心波长精确对准技术;测量信号和参考信号的获取与比值处理技术。对测量系统的光路、气室以及电路进行了设计,给出了以锁相放大器为核心的微弱信号检测电路和微型计算机处理电路。利用虚拟仪器技术,将采集的信号进行解调及加工处理和计算,用软件代替了复杂的硬件电路,简化了设计。得到的瓦斯浓度能够在图形界面上显示,并进行保存,以便用于瓦斯突出,瓦数预测等其它后续工作。进行了光纤甲烷气体传感系统的实验研究,验证了系统的可行性,并给出了实验结果。更多还原

【Abstract】 With the rapid development of industry and agriculture, the safety and environment protection of mine, oil field and electric power system is very important. Thousands of large-scale power factories and mine exhaust a great deal of flammable, explosive and poisonous gas in the air, and the living space and safety of human is seriously menaced, so rapid and real-time measurement of the gas is very important for safety production of mine and environment protection.In this paper, the main component of mine gas methane is used as a research sample. An optical fiber gas measurement system is set up based on spectrum absorption method. The advantages of this system is high sensitivity, high responding speed, freedom from inflammation and explosion, large dynamic range and freedom from poisoning, and the detecting segment can be placed in the flammable, explosive, poisonous places that people can’t come in and instruments can’t be placed in. Thus the concentration of methane can be real-time detected, and the system will give an alarm to people when it is dangerous, so the explosive accident caused by gas in mine can be avoided.After analyzing the theory of near-infrared selective absorption of gas, we describe the academic base of the measurement of the gas by absorption theory.The absorption spectra of methane are confirmed and the spectra characteristics which is fit for low-loss optical fiber to transmit a long way is also discussed. Distributed feedback laser diode (DFB LD) is used as a light source and light source modulation harmonic measurement is presented in this paper. The ratio of the fundamental and second harmonic signal can be used for eliminating the interference owing to light power changing. The mathematical model of gas concentration harmonic measurement is built up.Near-infrared light intensity stability technique of the light source, techniques of DFB LD’s frequency locked to the gas’absorption line and the measured signal and reference signal’s acquiring and ratio processing techniques are discussed in detail. Light path, gas cell and circuits of the system are designed and the system components including lock-in amplifier, weak signal measurement circuit and microcomputer processing circuit are also shown.A data acquisition and analysis system based on the virtual instrument technique was designed. With the powerful digital processing ability of the computer, the signal has been analyzed and displayed in user-friendly interface, and the saved history data can also be used in other related work.Experimental research of the optical fiber gas sensor for methane has been completed and the feasibility is enhanced. The results of experiments are shown in the end.更多还原