为了提高测量精度,对光线的有效利用率和最佳光程的选择进行了推导和优化。首先应用光线追踪法模拟CO2气室光路结构,计算光线的有效利用率;其次通过分析红外探测器接收到的光线，计算光程长对测量结果贡献率的影响，得出4.26 μm波长下CO2的最佳光程为31 mm。据此设计了CO2体积分数测量系统,并对20×10-6~1 500×10-6范围内的标准气体进行了测量。实验结果表明，该系统的测量精度可达到50×10-6。

In this paper, a development of a non-dispersive infrared (NDIR) CO2 gas measurement system with an optical path length of 31 mm is described. The system improves its accuracy by optimizing the optical path and the light efficiency. Firstly, the ray tracing approach is used to simulate the light path of the chamber, so the light efficiency can be calculated. Secondly, based on the simulation result of the sensor that every different optical path length has its own contribution to the measurement, the optimized optical path length for CO2 measurement in the wavelength of 4.26 μm is 31 mm. Then the CO2 volume fraction measurement system is designed and tested by measuring the standard gas whose concentration is in the range of 20×10-6~1 500×10-6, and the experimental results show that the measurement accuracy of the system can reach 50×10-6.