Study And Design Of Thermal Conductivity Detector For Gas Chromatography

With the rapid development of the petroleum, chemical, metallurgical and biology,morestringent requirements are raised for the qualitative and quantitative analysis of the materialelements,so the need for more speed, high-sensitivity, the scope of application of analyticalmethods and instruments is pressing.As a representative of modern analytical instrument,gaschromatography has been widely used in the field of biology, medicine and chemistry.There are many kinds of detectors for gas chromatography to use,such as FID(FlamIonization Detector),ECD(Electron Capture Detector),PID(Photo Ionization Detector)andTCD(Thermal Conductivity Detector).TCD is widely deployed in commercial gaschromatograph because it responds to all of material,has some advantages of the simplestructure,reliable performance,accurate quantization,low cost and durable and isnon-destructive detector.This paper systematically explicates the intelligent technology ofthermal conductivity detector for gas chromatography.Five parts which are the principle and performance characteristics of GC,the principle,working conditions and circuit design of TCD,the development of embedded Linux systemand the transplantation of drivers are introduced in this paper.Firstly,the paper introduces theorigin of topic.Secondly,separating principle,characteristics,comparison with other methodsof GC and factors influencing the properties of GC were discussed.On the basis of detectionprinciple of GC,the detecting principle of GC is analyzed and the choice of the volume ofpool,thermosensitive element,the carrier gas and bridge flow play a vital role for designing forTCD,which has some advantages of stable baseline,high sensitivity and a wide range ofdetection.As the level of sensitivity affects the TCD detection range,the design of TCDconstant current source is necessary to improve the sensitivity and the design of differencevoltage acquisition circuit is necessary to measure the signal of differential voltage output ofcurrent bridge.The signal are processed by A/D convertor and the microcontroller and thecomposition and content of material were detected.In this process,the choice of appropriateA/D convertor and microcontroller are necessary and SCR is adopted to controltemperature.As the chromatography can be used flexibly and conveniently,the transplant ofEmbedded Linux System for the main control board of chromatography consists of U-Bootand Linux kernel porting,construction of root file system and driver porting for expansion ofserial port,network card,LCD and USB.The sample was measured and analyzed after thetransplant of system was successful.Then,the curve of determination of sample was obtainedin the chromatography workstation.Compared with the standard curve of chromatography ofsample,the composition and content of material were measured.The application anddeveloping trend of GC in the future have also been discussed in the end.