Mainstream NDIR breathing CO₂ monitoring system based on new light chamber structure

Aiming at the problem of low sensitivity and low signal-to-noise ratio of mainstream non-dispersive infrared (NDIR) breathing CO₂ monitoring systems, the method using a compound parabolic concentrator (CPC) to improve the performance of the monitoring system was proposed. ZEMAX was utilized to simulate optical chambers, optimize CPC and commonly used straight cylinder concentrator and cone concentrator. The mainstream integrated method of single source and double light path was used to design the chamber of the monitoring system. STM32F100 was selected as the main control chip to control the hardware system. CO₂ concentration calibration and real-time human breathing detection experiments were performed on monitoring systems with different optical chamber structures, and the corresponding relationship between CO₂ concentration and system output signals and CO₂ waveform diagrams were obtained. The results show that the CPC optical chamber has a simulated optical efficiency of 4.3%, which can be up to 89.77 times higher than commonly used concentrators; the monitoring system equipped with CPC has a sensitivity and signal-to-noise ratio of 8.940 7 and 24.65, which can increase the sensitivity by up to 3.811 times and the signal-to-noise ratio by 1.926 times compared to systems equipped with common concentrators; And the system installed with CPC runs stably, responds quickly, and can display the capnogram of the subject in real time.