Development Of A Portable Breath Detector Based On Integrated Micro Chromatographic Chip

There are a variety of volatile organic compounds(VOCs)contained in the exhaled breath of the human body.The changes in their concentration are closely related to the health of the human body.By detecting these VOCs,human diseases can be detected as early as possible and their changes can be tracked in real time.It is of great significance to ensure the health of the human body.The traditional large gas chromatograph has been widely used in the field of gas detection due to its high detection accuracy and good repeatability.However,its high price,complex operation logic and huge size limit its application in the field of human breath detection.With the development of MEMS technology,portable gas chromatograph,which has the advantages of small size,low power consumption and fast detection,has gradually become a new research hotspot.In this thesis,a portable breath instrument based on the integrated micro chromatographic chip was developed for the detection of human gas exhalation,which can be used for the separation and detection of the VOCs breath characteristic gas of by human diseases.The main research work is as follows:According to the application requirements of low power consumption,good portability,and high accuracy of multi-component detection in breath detection,an embedded measurement and control system was proposed.Based on the STM32 main control chip,designed the voltage regulator circuit,solenoid valve drive circuit,temperature acquisition circuit analogto-digital conversion circuit,and took measures of electromagnetic shielding and other antiinterference design,making noise of the detector less than 0.1mV,and the power supply noise less than 1mV.Based on the STM32 open source library,the measurement and control software of the portable breath detector was developed,and the RS232 serial communication,SPI communication protocol,and refresh and display software of the serial display screen were developed,so that the instrument can meet the application requirements of breath detection.Aiming at the problem of large baseline noise of metal oxide gas sensor,by comparing various filtering algorithms,the moving average filtering algorithm was used to effectively reduce the baseline noise of the gas sensor,so that the instrument has a lower gas detection limit.In order to improve the separation characteristics of the integrated micro chromatographic chip,the fuzzy PID temperature control algorithm of the integrated micro chromatographic chip was studied.Through parameter optimization,the temperature control accuracy of the integrated micro chromatographic chip reached ±0.05℃,which reached the temperature control accuracy of the commercial chromatography column thermostat.Through the assembly and debugging of key components such as miniature chromatographic chip,pump,solenoid valve,sensor,etc.,a portable breath instrument has been successfully developed.A series of tests to breath characteristic VOCs were carried out on the instrument,and the results show that,the instrument can effectively detect isoprene,n-pentane,n-nonane,ethanol and other gases.At the same time,by adjusting the chip temperature and carrier gas pressure,the influence of temperature and pressure on the separation characteristics of mixed gases such as isoprene and n-nonane is obtained.Further tests show that the detector has accurate gas recognition capabilities,good gas quantitative analysis capabilities and repeatability.The developed portable gas detector has a volume of only 35cm×25cm×15cm,a power consumption of only 30 W,and a detection time of less than 15 minutes.It can detect a variety of VOCs breath characteristic gases related to human diseases,with a detection limit of 1ppm,and Good repeatability,qualitative and quantitative analysis capabilities.The development of this instrument has laid a solid foundation for the development of human breath POCT detection technology.