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也许参考一下： http://www.chromatographyonline.com/electronic-control-carrier-gas-pressure-flow-and-velocity


Electronic Control of Carrier Gas Pressure, Flow, and Velocity

Oct 01, 2014
By John V. Hinshaw

LCgc North America

Volume 32, Issue 10, pg 786-795

Have you wondered how your gas chromatography (gc) system sets and controls gas pressures, flows, and carrier gas velocities electronically? Here, we describe requirements for and the operation of electronic gas control systems for gc columns and detectors.
Computerized or electronic pneumatic control (EPC) systems for carrier gas, split flow control, and detector gases abound in modern gas chromatographs (gc), as well as in headspace samplers and column switching systems. The accuracy and repeatability of EPC are superior to that of manual adjustment, and the improved control of instrument parameters greatly reduces the possibility for making gas-related mistakes. Computerized pneumatics excel at controlling column pressure drop or detector gas flow rates. An EPC system generally relieves operators from having to make repetitive adjustments and measurements with a flow meter and stopwatch. However, running an EPC system blindfolded, so to speak, by never cross-checking actual gas behavior with selected set-points, only invites trouble. Like any computer system, the results can only be as good as the column and gas parameters that a user enters. Thus, a good working understanding of how an EPC system works and what goals are to be accomplished is essential for obtaining the best possible results.
How It Works

In an EPC system, gas flows from the gas supply input, through a metering valve, into a pressure or flow transducer, and then out to the device — inlet, detector, or other gc component — that consumes the gas. The gc system sends a set-point value to the EPC controller, which returns the measured flow or pressure value from its transducer. The set-point and actual values are compared in the EPC system, which adjusts the metering valve as required to maintain the desired set point. The EPC controller incorporates column and carrier gas characteristics to determine the necessary pressure drop at any given moment. Atmospheric and gas supply pressures plus controller temperatures are included as required to compensate for drift and instabilities.

In the simplest configurations an EPC channel acts as a carrier gas flow controller for a packed column or controls a detector gas, such as air or hydrogen, for flame ionization detection (FID). Two controllers — one pressure and one flow — can provide the split flow and inlet pressure for a capillary column inlet splitter. Other more complex applications include pressure or flow controllers for auxiliary devices such as purge-and-trap or headspace samplers, or pressure-switching controllers for multidimensional column systems.
Computer-controlled pneumatics cannot prevent operators from selecting inappropriate column pressures or split flow rates. An operator may easily establish incorrect conditions and become misled as to the reasons for a problem. Because of their complexity and flexibility, computerized pneumatic systems offer analysts more opportunities for errors.
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感谢老师！终于找到需要的资料了！！！疑惑终于解开了。