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根据甲烷(CH4)分子在中红外波段的吸收特性并利用宽光谱红外热辐射光源(IR55),研制了一种基于中红外吸收光谱技术的双通道差分CH4检测仪。通过对双通道探测器(3.31μm和3.90μm)输出的两路信号进行差分处理,有效抑制了系统噪声。给出了系统的检测原理和结构,表征了光源和探测器的光学特性。为了提高聚光效率并增大光程,设计制作了球面反射镜开放气室,其半径约20cm。配备了16种不同浓度的CH4气体样品,开展了气体标定实验,得到了气体浓度与双通道信号幅值电压的关系表达式。误差实验结果显示,对1 6种气体样品的检测误差小于12.4%。对体积分数为5×10-4的CH4气体样品开展的长达10h的浓度测量实验表明,检测结果的相对波动范围为±10%。对测得的实验结果进行数理统计,其标准差为2.06×10-5,进而得到该检测仪的检测下限约为6.18×10-5。
According to the absorption characteristics of methane (CH4) in the mid-infrared band and the use of a wide-spectrum infrared thermal radiation source (IR55), a dual-channel differential CH4 detector based on mid-infrared absorption spectroscopy was developed. By differentiating the two signals output from the two-channel detectors (3.31 μm and 3.90 μm), the system noise is effectively suppressed. The detection principle and structure of the system are given, and the optical characteristics of the light source and the detector are characterized. In order to improve the condenser efficiency and increase the optical path, a spherical reflector open air chamber is designed and manufactured, with a radius of about 20 cm. Equipped with 16 different concentrations of CH4 gas samples, carried out a gas calibration experiment, obtained gas concentration and dual-channel signal amplitude voltage expression. The error experiment results show that the detection error of 16 gas samples is less than 12.4%. Concentration measurements up to 10 h for a CH4 gas sample with a volume fraction of 5 × 10 -4 showed a relative fluctuation range of ± 10%. The measured results of the mathematical statistics, the standard deviation of 2.06 × 10-5, and then get the detection limit of the detector is about 6.18 × 10-5.