【作者】 撒继铭；

【导师】 周祖德； 陈幼平； 张冈；

【作者基本信息】 华中科技大学 ， 机械电子工程， 2007， 博士

【摘要】 通风不良或密闭的环境中对易燃易爆和有毒有害气体的监测对保障人身健康和安全具有非常重要的意义,在此类场合中一般采用技术比较成熟的电式气体传感器,但电式气体传感器在使用过程中会有产生电火花并引发爆炸的可能,而且此类气体传感器往往存在容易老化和中毒的缺点。由于光纤传感器采用光而不是电作为信息载体,所以不存在产生电火花的安全隐患问题。正是因为光纤气体传感器具有安全方面的独特优点,而且适宜在各种恶劣的环境条件下工作,所以光纤气体传感器的研究和开发逐渐成为目前气体传感器研究的热点。本文主要针对一氧化碳(CO)气体,对光纤气体传感器的理论、建模和设计实现进行研究。首先,基于气体分子吸收光谱理论和比尔-朗伯定律,分析了差分吸收型气体传感器的数学模型和基于窄带光源的谐波检测光纤气体传感器的数学模型,在此基础上提出了基于谐波检测的光纤气体传感器的数学模型的改进方法,即基于差分后谐波检测的光纤气体检测模型。此外,还对基于窄带光源的谐波检测光纤气体传感器进行了仿真研究。基于差分后谐波检测的光纤气体检测模型利用参考光路与检测光路光强的差分消去基波分量,对差分后的信号再进行二次谐波检测得出气体浓度。使用该方法提高了系统检出二次谐波分量的能力,同时有效地提高了系统的分辨率。根据上述理论分析,设计开发了基于差分后谐波检测的光纤传感器系统。在传感器光路系统设计中,提出了一种基于串联自聚焦透镜组的透射式气室。对基于串联自聚焦透镜组的透射式气室的数学模型进行了分析,并完成了气室结构的设计与开发。对于一般的基于自聚焦透镜组的透射式气室,通过增加吸收光程来获得更高灵敏度。但在对传感器尺寸有限定的场合不能任意加长气室,在这种情况下,可以将多对自聚焦透镜组串联使用,即采用基于串联自聚焦透镜组的透射式气室的结构。采用这种结构的气室可以实现在不增加气室长度的情况下使吸收光程增长。根据光电微弱信号检测的原理以及差分后谐波检测的光纤气体检测模型,完成了光电微弱信号检测电路系统设计。设计实现了基于差分后谐波检测的微弱信号处理电路、前置放大电路、差分电路、调制电路和光源温度控制电路及电流驱动电路等。最后对传感器样机进行了系统实验研究,实验结果表明基于差分后谐波检测原理和串联自聚焦透镜组的透射式气室结构的光纤气体传感器具有良好的检测效果。更多还原

【Abstract】 Electronical gas sensors are advanced, but this type of sensors have some shortcomings such as causing explosion, sensitive material poisoning. Since optical fiber gas sensors adopt optic as information carrier, this type of sensor has special advantage in security. And this type of sensor is fit for working in bad conditions. Therefore research and development of optical fiber sensor is gradually become the highlight of gas sensors’research. Optical fiber gas sensors are studied systematically in this dissertation, which include theoretical modeling, developing and testing of prototypes.Based on Principle of absorption spectrum and Beer-Lambert law, mathematical model of gas sensor based on difference absorption was analyzed. And harmonic detection mathematical model of optical fiber gas sensor based on narrowband optical source was analyzed. Then improved harmonic detection mathematical model of optical fiber gas sensor was presented. We call this model as difference-harmonic-detection model. Simulation research on harmonic detection optical fiber gas sensor based on narrowband optical source was processed. Using the difference between referenced light intensity to metrical light intensity, we can counteract the fundamental wave component. Detecting 2nd harmonic of difference signal, we can obtain the gas concentration. By using this method, system’s ability of detecting 2nd harmonic component is improved, and system’s resolving power is increased too.According to analysis above, structure of difference-harmonic-detection optical fiber sensor system was designed. In optical design, we present a method that using cascaded GRIN Lens couples to compose a gas cell. Mathematical model of transmission type of gas cell that based on cascaded GRIN Lens couples was analyzed. And structure of gas cell is designed and developed. If the other condition is fixed, with increasing of optical path length, sensor’s sensitivity is enhanced. For transmission gas cell based on GRIN lens, the same method is usually adopted. However, for some of sensors, the formal size is limited. Especially, the length is limited. To shorten sensor’s size and length, and enhance sensor’s sensitivity, a method that using cascaded GRIN Lens couples to compose a gas cell is presented. With this method, the optical path length is increased and the detection sensitivity of the gas cell is greatly increased. According to principle of Photoelectricity Weak Signal Detection and mathematical model of difference-harmonic-detection optical fiber sensor, the system of Photoelectricity Weak Signal Detection is designed. The circuit of Photoelectricity Weak Signal Detection, preamplifier circuit, difference circuit, modulation circuit, optical source thermal control and current drive circuit etc. are designed.At last, based on the research above, the prototype of an optical fiber gas sensor is developed. Experimental results show that optical fiber gas sensor based on difference- harmonic-detection and structure of cascaded GRIN Lens couple has good detection effects.更多还原