摘要
随着工农业的迅速发展，矿井、油田、电力系统安全保护以及环境保护成为越来越值得重视的问题。数以千万计的大型动力工厂和矿业部门排放出大量的易燃、易爆、有毒、有害气体，使人类的生存环境和人身安全受到严重威胁，因此对这些气体进行快速、实时检测对于工矿安全生产及环境保护有特别重要的意义。
本文以矿井瓦斯的主要成分甲烷为目标气体，研究基于光谱吸收方法的全光纤气体检测系统。该系统具有灵敏度高，响应速度快，动态范围大，防燃防爆，防电磁干扰，不易中毒等优点，可将传感头放置在人和仪器不易进入的易燃易爆、有毒等恶劣环境中，实现在线遥测，从而达到实时检测甲烷浓度、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。并确定了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。
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。
With the rapid development of industry and agriculture, safety and environment protection of mine, oil field and electric power system is of great importance more and more. Thousands upon 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's are 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 system has the advantages of high sensitivity, fast 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 remote 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.
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.
引文
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