Research On Non-dispersive Infrared Detector For CO₂ Concentration

The concentration of CO2 is an important parameter in the fields of environmental protection,industrial process analysis and control,medical diagnosis,etc.Furthermore,as one of the important components of the atmosphere,CO2 is in close correlation with people's production and daily life.Hence the monitoring of CO2 concentration is of vital theoretical significance and practical value.Therefore,it is very important to develop a sort of miniaturized detectors for CO2 concentration with good selectivity and stability.In this dissertation,a new system to CO2 concentration detection based on non-dispersive infrared was designed specific to the deficiencies of the traditional CO2 concentration detector.Infrared source and electrical modulation were used instead of traditional light source and mechanical modulation,which avoided the complex and expensive motor modulation system of traditional NDIR,to greatly reduce the cost and power consumption of the system.On this basis,the hardware and software platform of the non-dispersive infrared CO2 concentration detector system was constructed,and the related tests and experiments were conducted on it.The following researches were mainly made in this dissertation:(1)The principle of the gas infrared spectra absorption was studied,and the deficiencies of the traditional gas concentration detector was analyzed.On this basis,a new system to non-dispersive infrared CO2 concentration detection without movable components was designed based on the features of IRL715 infrared source and PYS3228G2/G20 pyroelectric infrared detector.(2)Studies and analysis of the components that were relevant to the required infrared source,pyroelectric infrared detector and optical chamber were carried out,and the design of the whole light path system was completed.(3)Hardware circuits including LED driving circuit,preamplifier circuit,filter circuit,etc.were designed and maded,and a system debugging was conducted.(4)Computer programs were written in C language in IAR EW430 integrated environment.Microcontroller procedures for signal collecting and filtering were mainly programmed in this research.(5)The calibration of the instrument made above was done in a lab environment using standard CO2 gas,and related tests of CO2 with a gas concentration in the range of 0?3%were taken.Through the experimental tests,it was concluded that the maximum absolute error of the instrument was less than 0.1%,the repeatability less than 2%,and the response time was less than 15 seconds.