Research On Infrared CO₂ Gas Sensor System With Constant Temperature And Low Humidity Control Function

The increasing concentration of CO₂gas in the atmospheric environment has brought many bad influences to the global ecological climate environment and human production and life.Therefore,it is very important to design a CO₂gas concentration detection system which can adapt to various environmental conditions.In this paper,an infrared CO₂gas sensor with constant temperature and low humidity control function is proposed,and its detection accuracy and anti-interference ability are analyzed through a series of experiments.Firstly,the infrared light source and detector of the optical system of gas sensor are selected,and a flat cone sensor sampling chamber with constant temperature and low humidity control function is proposed.The reflection and light intensity distribution of infrared light in the sampling chamber are simulated and analyzed by Zemax optical software.The ANSYS FLUENT software is applied to simulate the constant temperature control of the sampling air chamber,and the feasibility of constant temperature control is verified theoretically.In terms of improving the sensor's ability to resist environmental temperature and humidity interference,the hardware compensation of the sensor is proposed by PID constant temperature control algorithm and 3A molecular sieve humidity reduction.Secondly,based on the above optical system design,the peripheral control circuit system of CO₂gas sensor is designed.STM32 microcontroller is used as the core of the circuit system to realize the modulation of infrared light source by DAC.The detection signal of the detector is amplified and A/D converted by ICL7650 chip and AD7794 chip,and the detection of CO₂gas concentration is effectively realized.The system is thermostatically controlled by combining temperature and humidity acquisition with constant temperature heating adjustment,and the temperature and humidity signals and concentration information are transmitted and displayed by the upper computer and Bluetooth module.Finally,the concentration calculation formula of the detection system is determined by calibration experiment,and the error performance of the system is tested.The experimental results show that:In the detection range of 0?2003ppm,the fitting error of the system is within±70ppm,and the repeatability and stability errors are within±3.3%and±3.7%respectively,which meets the application requirements in actual scenes.In addition,the temperature influence experiment and humidity influence experiment are carried out on the sensor detection system respectively.The results show that when the ambient temperature gradually deviates from the calibration experimental temperature in the range of-10??40?,the error of CO₂gas concentration detection value is gradually larger.In the range of30%?80%environmental humidity,the increase of environmental humidity will also lead to the increase of detection error.In view of this phenomenon,the sensor detection system is compensated by the constant temperature control module and the low humidity control module.After the compensation and correction,the temperature and humidity drift phenomenon of the detection system is well suppressed,and the detection error of the system can be controlled within±105ppm in complex temperature and humidity environment.The research meets the needs of real-time monitoring of CO₂gas concentration in complex environment,and has certain reference value for developing high-performance gas sensors.