GB833864A - Chromatographic gas analysis sample control system - Google Patents

Abstract

<PICT:0833864/III/1> An apparatus for repeatedly producing and supplying gas samples of fixed volume and constant mass to a standard chromatographic column, consists of a tube of fixed volume to which the gas is fed and is then connected to one of a pair of contractible and expansible housings of the bellows type, working in opposition against a common flexible diaphragm, the other housing containing a reference gas sealed therein, whereby any variations in temperature during the preparation of the series of samples resulting in a variation in the density of the gas samples, is exactly compensated by an increase/decrease in pressure on the sample to obtain the same mass of the gas. In one form of apparatus the gas to be sampled enters a tube 20, to the standard fixed volume tube 12, and after control by the double bellows assembly 10, is swept by carrier gas admitted through a tube 19 into the chromatographic column 15 at the base of which is a detector 16 producing a signal 17. The admission, isolation, control, and injection of the sample gas into the carrier gas is operated automatically by switch valves 1 . . . 5, controlled by solenoid-operated pneumatic valves in the assembly 13 in accordance with a preselected timing programme. The bellows 27 is fed with a metered quantity of a reference gas, preferably the same as the gas under test to avoid variations in physical characteristics. The upper bellows 32 is connected by a pipe 25 to the gas sample to be controlled, and is provided at the top with a bleed valve 38 pressing against a seating 39 and also a diaphragm 37. Excess gas leaves through a pipe 41, and creates a backpressure in tube 42 connected to a jet 35 through which a gas flows from an inlet 43, until the pressures are in balance with that of the reference bellows when diaphragm 34 closes the end of jet 35. A spring-loaded screw 36 provides adjustment of the diaphragm to required conditions. The bellows assembly 10 and fixed volume tube 12 are housed in a chamber to maintain a uniform temperature. In modifications (not shown), two bellow chambers are replaced by a fixed chamber separated into upper and lower chambers by a sensitive flexible diaphragm.