基于中红外激光吸收光谱的CH_(4)浓度检测仪研究

Research on CH_(4) Concentration Detector Based on Mid Infrared Laser Absorption Spectrum

针对公共安全生产和气候环境研究领域对CH_(4)浓度测量的需求,基于中红外激光吸收光谱技术,利用函数发生器、低噪声电流驱动器、温度控制器和7.323μm波段量子级联激光器集成输出模块,结合气池、光电探测器和数据采集系统完成对CH_(4)浓度检测仪的设计与实现。采用波长调制方法对CH_(4)浓度测量展开研究,通过一次谐波平均值归一化处理二次谐波来抑制低频噪声,同时消除了光强波动影响。实验证明在标定浓度范围内,CH_(4)气体浓度值与归一化二次谐波峰值具有良好的线性相关,相关系数高达0.99997。Allan方差分析表明,在积分时间为10 s时,系统的检测下限为7.19 ppmv。结果表明,CH_(4)浓度检测仪整体性能适用于煤层气开采和储运过程中泄漏等需要及时报警的场景。

In order to meet the need of CH_(4)concentration measurement in the field of safe production and climate and environment research,function generator,low-noise current driver,temperature controller and 7.323μm quantum cascade laser are integrated as an output module based on mid infrared laser absorption spectroscopy technology,combined with the gas pool,photoelectric detector and data acquisition system,the design and implementation of CH_(4)concentration detector are completed.The wavelength modulation method is used to study the measurement of CH_(4)concentration.By normalizing the second harmonic with the average value of the first harmonic,the low-frequency noise is suppressed and the influence of laser intensity fluctuation is eliminated.The experimental results show that the CH_(4)concentration has a good linear correlation with the normalized second harmonic peak,and the correlation coefficient is as high as 0.99997.The result of Allan variance analysis shows that the lower detection limit of the system is 7.19 ppmv when the integration time is 10 s,indicating that the proposed detector is suitable for leakage detection during the process of gathering from coal mine,transportation,and storage of coal bed gas.