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为了在中红外(MIR)CH4浓度检测中降低检测下限和提高探测灵敏度,提出了一种非对称椭球聚光镜气室。在充分考虑线光源和双窗口探测器外形及尺寸的条件下,建立了完备的非对称椭球聚光镜气室物理模型,导出了直射功率、反射功率、聚光效率和灵敏度系数的表达式。通过计算分析,得到了同时获得较高聚光效率和高灵敏度系数的条件,以及非对称椭球聚光镜的优化参数。利用优化制作的非对称椭球聚光镜气室,建立了CH4检测系统。检测结果显示,系统的检测下限约为5×10-6;低浓度范围(0~100×10-6)的探测灵敏度约为6~7×10-6;在高浓度范围内(1~40×10-3),探测灵敏度随气体浓度增加而增加,约为20~160×10-6。检测结果表明,优化后的CH4检测系统实现了较低的检测下限和较高的灵敏度。
In order to reduce the detection limit and improve the detection sensitivity in the mid-infrared (MIR) CH4 concentration detection, an asymmetric ellipsoidal condenser chamber was proposed. Under full consideration of the shape and size of linear light source and double window detector, a complete physical model of gas chamber of asymmetric ellipsoidal condenser was established, and the expressions of direct power, reflected power, condenser efficiency and sensitivity coefficient were derived. Through the calculation and analysis, the conditions for obtaining high condensing efficiency and high sensitivity coefficient at the same time, as well as the optimization parameters of the asymmetric ellipsoidal condenser are obtained. The CH4 detection system was established by using the optimized asymmetric ellipsoidal condenser chamber. The detection results showed that the detection limit of the system was about 5 × 10-6. The detection sensitivity of low concentration range (0 ~ 100 × 10-6) was about 6 ~ 7 × 10-6. In the high concentration range (1 ~ 40 × 10-3), the detection sensitivity increases with the increase of gas concentration, about 20 ~ 160 × 10-6. The test results show that the optimized CH4 detection system achieves lower detection limit and higher sensitivity.