【作者】 郭增军；

【导师】 王玉田；

【作者基本信息】 燕山大学 ， 测试计量技术及仪器， 2003， 博士

【摘要】 气体传感技术是当今传感器技术领域研究的一个重要前沿课题。以半导体激光器或发光二极管作为光源的气体传感技术在灵敏度、选择性、动态范围、信噪比和响应时间等方面比传统方法具有诸多优点。特别是运用光纤技术而构成的光纤传感器因传感头与检测电路和信号处理电路实现完全的电隔离，使系统安全可靠。光纤通信技术的发展使相对低价、工作于常温、高质量的近红外激光和发光二极管可广泛获得，这些发光光源的发射波长与光纤的三个低损耗窗口相一致，也与许多环境和工业气体的泛频或复合吸收谱线相一致。因此光纤气体传感器可在人和仪器不易进入的高温、有毒有害等危险环境进行远距离遥测遥控，实现在线检测。本文以甲烷(CH4)气体为测量目标气体，详细研究了基于红外吸收的全光纤传感的理论和实验方法，为气体的全光纤在线检测提供完善的数学模型和设计系统。主要研究内容如下：(1) 应用分子光谱理论和实验数据给出了甲烷气体在联合带v2+v3和泛频带2v3的精细参数，包括吸收线的中心波长、吸收线间隔、吸收线强度分布、吸收线线型和线宽，为系统设计选择合适波长提供依据，消除交叉敏感。(2) 依据朗伯－比尔（Lambert-beer）定律和光学信息处理技术，给出了两种常用半导体光源LED和DFB LD与红外吸收线作用后，光谱分量强度与气体浓度关系的解析表达式。(3) 由于气体近红外吸收系数很小，直接应用光吸收检测时，信号中不仅有光路干扰，还有很大部分与浓度无关，信号难以放大，检测灵敏度受到限制，因此要减小和消除检测信号中与浓度无关的成分。(4) 差分吸收检测和波长调制谐波检测是气体光吸收检测的两种基本方法。谐波检测根据光源不同，系统设计有较大不同，但都是基于导数光谱特性以及气体吸收线型偶对称特性（或F-P腔多纵模谱线的对称性），利用基波信号作为反馈信号可以精确锁定光源中心波长与气体吸收线的中心位置。(5) 给出了系统详细的以锁相放大器为核心的微弱信号检测电路和微型计算机控制电路。(6) 进行了光纤甲烷测量系统的实验研究，包括LED光谱特性，透射光强度与甲烷气体浓度的关系以及标定结果等。更多还原

【Abstract】 Gas-sensing technology is an important forefront topic in the research field of sensing technology now. Gas-sensing technology, which employs semiconductor laser and light emitted diode as light resource, has multitude advantages over traditional approaches, such as high sensitivity, multiple selection, wide dynamic range, good signal to noise ratio and quick response time. Especially optical fiber sensor is more safe and reliable, for electrical insulation has been realized by the separation of optical fiber sensor from detection and signal processing circuit. With the rapid development of optical fiber communication technology, low-cost and high quality near inferred laser and light emitted diode working at room temperature become widely available. The emit wavelength from these light resource is not only consistent with the three low-decay windows of fiber optics, but also with many wide-frequency or recombination absorption spectrum of environmental and industrial gases. Therefore optical fiber gas sensor can fulfill on-line measurement in high-temperature, poisonous and dangerous situation where human being and traditional instruments can hardly accomplish.In this paper, CH4 is used as a research example. Based on the theory and experi- mental approaches of inferred absorption all optical fiber sensing, mathematical model and system design for all optical fiber on-line gas measurement are presented. The detailed research contents are as following:(1) Based on molecule spectrum theory and experimental data, presented are fine parameters of CH4 combined frequency band v2+v3 and wide frequency band 2v3, including absorption spectrum central wavelength, line space, intensity distribution, line type and line width. These fine parameters have played solid foundation for measurement wavelength selection, and effectively eliminated cross sensitivity. (2) According to Lambert-beer law and related optical signal processing technology, analysis formula is presented to express the relationship between spectrum intensity and gas density after the two widely used semiconductor light resource LED and DFBLD functioned with inferred absorption spectrum line. (3) Since the gas inferred absorption coefficient is very small, when the light ab- sorption measurement is directly used, there are not only light route interference, but also no relationship between content and density. Then the signal is very difficult to amplify,<WP=9>and measurement sensitivity is strictly limited. Therefore we should try to avoid the signal measurement component, which has no relationship with density.(4) Difference absorption measurement and wavelength modulation harmonic mea- surement are two fundamental approaches for gas light absorption detection. For di- fferent light resource, system designs for harmonic detection have great differences, but all of them are based on derivative spectrum characteristics and even symmetric gas absorption line (or F-P chamber multiple vertical pattern symmetry). With ground wave as feedback signal, the central wavelength can be precisely locked on the location of gas absorption central position.(5) Presentedthe detailed system components including lock-in amplifier, weak signal measurement circuit and microcomputer controlled circuit.(6) Experimental research has been completed including LED spectrum characteri- stics, relationship between transmission light intensity and CH4 density, result analysis and calibration.更多还原