Research Of The Portable Gas Chromatograph Control System

Gas chromatograph is a very important analytical instrument, which can makequalitative and quantitative analysis and has excellent separating power for complexmixtures. It had been used as early as the1950s and the development of portable gaschromatography is one of the main research directions.Temperature is a very important parameter to portable gas chromatography. Forinjector, column, and detector, temperature control must reach certain accuracy.Column heater doesn’t used in portable gas chromatography, thus the temperaturecontrol is difficult. In this study, low heat capacity chromatographic technique wasused for heating chromatographic column. The accurate temperature control ofgasification chamber and chromatographic column was studied.The temperature control system included a PT100detector, a constant currentsource, and a data acquisition card. A new control method was presented to improvethe control accuracy for low-power systems, which can directly drive the heatingdevice through amplify power signal. The main control interface and subroutinewere exploited based on LabVIEW software, and the PID controller was used fortemperature control.To improve the control accuracy and reduce overshoot, the variable speed integraland integral limit methods were used. Besides, a PID and mixed control Bang-Bangmethod was used to maintain a high heating rate which achieved good results. In thetemperature control experiment, the control accuracy could reach to±0.1℃and theovershoot was below1.5℃. The value of temperature could be change at any time,and the control system also could achieve thermostatic temperature control andprocess control functionsFinally, putting the control system into a chromatograph, the clearly spectra wereobtained when test samples are benzene and xylene. The experiment verify thevalidity of the control system.