为了实现CO₂气体同位素的高性能检测，研制了高精度、高稳定性的激光红外多通池压强控制系统。硬件方面，采用压强传感器连接于多通池前、后端，检测多通池内部气压，主控制器通过PWM信号，调控多通池前、后端比例阀导通状态，从而实现压强的闭环控制。软件方面，采用Ziegier-Nichols工程整定方法，完成对P 、 I、 D 3个参数的确定。结果表明：多通池压强为60 Torr(1 Torr=133.322 Pa)时，控制精度为±0.04 Torr。试验中，利用研制的多通池压强控制系统对¹³CO₂、¹²CO₂气体分子在4.3 μm吸收光谱进行测量。随着气体压强从0.026~0.066 atm (1 atm= 101 325 Pa)，¹³CO₂和¹²CO₂气体分子吸收光谱的峰值随着压强增大而增大，吸收光谱宽度也随着压强的增大而增大。同时，利用红外气体检测系统对CO₂同位素丰度进行长达2 h的测量。CO₂同位素丰度均值为?9.081‰，测量值在?8.351‰~?9.736‰之间波动，最大偏差值为0.73‰。可以证明：该系统为红外CO₂气体同位素的高性能检测提供可靠保障。

In order to realize the high performance detection of CO₂ gas isotope, a multi-pass gas cell pressure control system with high precision and stability was developed in this paper. In terms of hardware, the pressure sensor was connected to the front and back end of the multi-pass gas cell to measure the inside pressure of multi-pass gas cell. The main controller regulated the proportional valves that were at the front and back end of the multi-pass gas cell via PWM signal, so as to realize the closed loop of pressure control. In terms of software, Ziegier-Nichols engineering setting method was adopted to determine three parameters P, I and D. The results show that the control accuracy is ±0.04 Torr (1 Torr=133.322 Pa) when the pressure of the multi-pass gas cell is 60 Torr. In experiment, the developed pressure control system of multi-pass cell was used to measure the absorption spectra of ¹³CO₂ and ¹²CO₂ gas molecules at 4.3 μm. With the increase of gas pressure from 0.026-0.066 atm(1 atm= 101 325 Pa), the peaks of the absorption spectra of ¹³CO₂ and ¹²CO₂ gas molecular increased with the increase of pressure, the width of the absorption spectra also increased with the increase of pressure. Meanwhile, an infrared gas measuring system was used to measure the CO₂ isotope abundance during two hours. The average isotope abundance of CO₂ is -9.081‰, and the fluctuation of measured values is between -8.351‰ and -9.736‰, with the maximum deviation of 0.73‰. It can be proved that the system provides reliable guarantee for high performance detection of infrared CO₂ gas isotope.