Design Of Carbon Dioxide Concentration Detection System Based On Ultrasonic Phase Difference Method

Carbon dioxide is a significant part of air and a significant industrial raw material.It is closely bound up with our production and life.Carbon dioxide detection technology can be used to monitor production and living environments.With the expanding of modernization and urbanization,global carbon emissions have tremendously increased the amount of carbon dioxide in the atmosphere,resulting in a serious "greenhouse effect".Therefore,it is necessary to detect the concentration of carbon dioxide.However,there has been a lack of carbon dioxide detection methods that can achieve large measurement ranges,high accuracy and high stability for a long time.Ultrasonic detection technology has the advantages of low power consumption,high stability,non-contact,etc.,and has been widely used in many fields.Therefore,this paper conducts a research on the carbon dioxide concentration detection system based on the ultrasonic phase difference method.In this paper,the ultrasonic measurement methods are studied,including the sound attenuation method,the time difference method and the phase difference method,and the ultrasonic carbon dioxide concentration detection scheme based on the phase difference method is determined by comparative analysis.The relationship between carbon dioxide concentration and ambient temperature,humidity and phase difference is theoretically analyzed,and a mathematical model for data processing and precision compensation is established.The hardware circuit design of ultrasonic drive circuit,signal conditioning circuit,phase difference detection circuit,single-chip microcomputer system and peripheral circuits,signal output circuit and power supply circuit has been completed.The software design of the main program,calibration program,infrared remote control program,temperature detection program,humidity detection program and signal output program of the ultrasonic carbon dioxide concentration detection system has been completed.In this paper,the experimental research and error analysis of the influence of ambient temperature and humidity are carried out,and the completed detection system is tested.The ultrasonic carbon dioxide detection system is in the low concentration range of 0～2%,the maximum absolute error is less than ±0.02%,and in the high concentration range of 2～100 %,and the maximum relative error is less than ±10% of the true value.The experimental results show that the measurement method has high accuracy when the concentration measurement range is large.