综合运用棱镜气室与谐波检测技术, 构建了适用于宽广浓度范围内的光纤甲烷检测系统。 以大气环境为背景, 基于比尔-朗伯(Beer-Lambert)定律在气体弱吸收时的近似表述, 利用背景扣除和比值处理技术, 实现了常压下甲烷不同浓度水平(0～20%)的检测。 利用渐变折射率透镜(GRIN)气室测量了甲烷在不同浓度时的直接吸收谱, 结合现有DFB-LD光源选择甲烷2ν3带的R5支(1 648.212 nm)作为被测吸收峰。 在不同浓度气体配置过程中, 进行了系统的在线实验, 结果表明系统示值与浓度变化间线性良好, 而且系统的稳定性和动态响应特性比较理想。 该系统可根据不同现场环境的甲烷浓度水平, 选择适当强度的吸收线, 通过步进电机调节棱镜中线间的距离, 进而改变气室内有效吸收光程, 拓展了仪器的应用领域, 可作为煤矿巷道或天然气管道沿线的瓦斯监测仪器。

A novel fiber methane detection system was constructed based on integration of prism gas cell and harmonic detection technique. The system can be applied to broad-range concentration detection. Grounded on the Beer-Lambert approximation, the detection of various concentration (0-20%) of methane was completed using subtraction of background and ratio processing method, as the atmosphere surroundings was treated as background. The direct absorption spectra for various concentration were measured using GRIN gas cell, combined with available DFB-LD, and the R5 line of the 2ν3 band of methane was selected as absorption peak. The system was tested online during gas mixing process and the linear relation between system indication and concentration variation was validated, while the stability and dynamic response characteristics was confirmed by experiments. The system sensitivity can be adjusted according to the concentration level of various field environments by changing the prism distance using step motor. So that, the system can be applied to various application fields and can be adopted as a monitoring instrument for coalmine tunnel and natural gas pipeline.