Stanford Research Systems RGA100, Operating Manual And Programming Reference

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6 Glossary of Terms
SRS Residual Gas Analyzer
Sensitivity calibration . The act of establishing a a correspondence between the change
in ion current and the corresponding change in partial pressure of the gas from which the
ion is produced. The correspondence might be represented graphically or as a table of
values. See also Sensitivity.
Space charge . The electrical charge carried by a cloud of free elctrons or ions. Space
charge can causes serious changes in the potential distributions of the ionizer, and
ultimately limits the pressure operating range of all RGA’’s.
Total Pressure . The average normal force per unit area exerted by all the gas molecules
impacting on the internal surfaces of the vacuum chamber. Units are typically Torr, mbar
or Pascal. Note: The SRS RGA is capable of collecting total ion currents that can be
turned into total pressure measurements with the help of gas dependent total pressure
sensitivity factors.
UHV . Abbreviation for Ultra High Vacuum. Pressure < 10
-9
Torr.