棱镜气室相较于传统渐变折射率透镜(GRIN)气室在灵敏度调节性及抑制干涉噪声方面优势明显。基于比尔朗伯(Beer-Lambert)定律在气体弱吸收时的近似表述,以大气环境为背景,利用背景扣除和谐波检测技术,实现了常压下甲烷不同体积分数水平(0-20 %)的检测。依据实测的甲烷在不同体积分数时的直接吸收谱,结合现有分布反馈式激光二极管(DFB-LD)光源选择2ν3带的R5支(1648.212 nm)作为被测吸收峰。气体配置过程中的在线实验表明系统示值与体积分数变化间线性关系良好,而且系统的稳定性和动态响应特性理想。该系统可根据不同现场环境的甲烷体积分数水平,通过步进电机调节气室内有效吸收光程,动态调整系统灵敏度,可作为煤矿巷道或天然气管道沿线的瓦斯监测仪器。

Compared with gradient index (GRIN) gas cell,the sensitivity of prism gas cell is easy to be adjusted and the interference noise is apt to be suppressed. Based on the Beer-Lambert law,detection of various volume fraction (0-20 %) of methane is completed by subtraction of background and harmonic detection method,as the atmosphere surroundings is treated as background. The direct absorption spectra of various volume fraction are measured using GRIN gas cell,combined with available distributed feedback laser diode (DFB-LD),where the R5 line of the 2ν3 band of methane is selected as absorption peak. The system is tested online during gas mixing process and the linear relation between system indication and volume fraction variation is validated,also the stability and dynamic response characteristics is confirmed by experiments. The system sensitivity can be adjusted according to volume fraction level of various field environments by changing the prism distance and using step motor. The system can be applied to various fields and can be adopted as monitoring instrument for coal mine tunnel and natural gas pipeline.