Pulsed gas injection for on-line calibration of residual gas analyzers

Abstract

Pulsed gas injection valves have been developed which deliver highly repeatable single bursts of gas in the 10−7–1 Torr l range. Although originally intended for studying dynamic vacuum phenomena, these valves appear to have interesting possibilities for on-line checking of residual gas analyzer calibration. The work chamber is pumped continuously during calibration. The almost instantaneous and predictable pressure increase in a chamber of known volume allows direct sensitivity measurements to be made provided the analyzer has a sufficiently fast response. Experimental results showing reproducibility and pressure waveforms for a manually triggered valve are summarized. An outline is given of a calibration procedure using pulses of noble gases of differing molecular weights. Preliminary results obtained with a simple electromagnetic valve capable of up to 100 pulses s−1 are also discussed.