Research On Four-component NDIR Gas Sensor With Constant Temperature And Low Humidity Contro

In view of the wide application scenarios of gases and the harm caused by improper application of gases,multi gas detection has become a hot topic of research at home and abroad.Traditional single gas sensors cannot meet people’s needs,so it is particularly important to develop a multi-component gas concentration detection system with high precision,good stability and being able to adapt to diverse environments.Therefore,this paper proposes a non dispersive infrared（Non-dispersive Infrared,NDIR）four component gas sensor with constant temperature and low humidity control functions,which realizes the concentration detection of CO,CO₂,CH₄,and SF₆ gases,and the sensor is analyzed through a series of performance test experiments.Firstly,the detection principle of the NDIR four component gas sensor is described,and the light source and detector of the optical system are selected based on the infrared absorption characteristics of the gas.A new reflective four petal-shaped sampling gas chamber is designed.Combined with Solid Works 3D modeling,Light Tools optical software is used to simulate and analyze the reflection and intensity distribution of infrared light in the sampling gas chamber,and the reasonable placement of the four detectors is determined,and the internal structure and size of the gas chamber are optimized.In order to reduce the impact of ambient temperature and humidity on the measurement of multicomponent gas sensors,a PID（Proportional、Integral、Differential）constant temperature control algorithm and molecular sieve dehumidification method are proposed to compensate for the temperature and humidity drift of the sensor system in hardware.Secondly,after making an optical gas chamber with constant temperature and low humidity control functions,a matching peripheral control circuit and software system are designed.The STM32 microcontroller was applied as the main control chip,and its PWM was used to achieve electrical modulation of the light source.Four ICL7650 channels are employed to amplify the electrical signals of each detector.Combined with a one out of four selector,the high-precision AD7794 chip is utilized to realize A/D conversion.The sensor is thermostatically controlled through temperature and humidity collection and constant temperature heating adjustment,and temperature and humidity signals and gas concentration information are transmitted and displayed through the upper computer and Bluetooth module.Finally,constant temperature and low humidity testing,gas calibration experiments,and sensor performance testing are systematically carried out.Within the temperature range of-10℃to 40℃,the temperature of sensor gas chamber can be controlled to be constant at 40℃.Within the humidity range of 30%to 80%,the humidity of the air chamber can be controlled at 18%,indicating a good effect of constant temperature and low humidity.Under this condition,the concentration calculation formulas for CO,CO₂,CH₄,and SF₆ are determined through calibration experiment fitting.The performance test results show that the repeatability and stability errors for measuring CO₂ are within 5.24%and±60 ppm in the gas concentration range of 0 to 2000 ppm,and the repeatability and stability errors for measuring CO are within 8.83%and±60 ppm in the range of 0 to 1000 ppm,and the repeatability and stability errors for measuring CH₄ are within 4.65%and±140 ppm in the range of 0 to 5000 ppm,and the repeatability and stability errors for measuring SF₆ are within 3.86%and±55 ppm n the range of 0 to 1000 ppm.A mixed gas scenario simulation test was conducted and it is found that the cross sensitivity of the NDIR four component gas sensor is low,and the system performance basically meet the requirements of practical scenario applications.