Stanford Research Systems RGA100, Operating Manual And Programming Reference

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Features and Operation 5-13
SRS Residual Gas Analyzer
Saving RGA files does not save any of the head parameters to that file since each RGA
Head has unique parameters due to minor variations in electronic and physical
properties. Head parameters cannot be changed unless an SRS RGA Head is connected
and turned on.
Sensitivity Factors
The RGA Head uses two sensitivity factors stored in its non-volatile memory. The
sensitivity factors, one for total pressure and one for partial pressure, are used as
conversion factors between the ion currents received form the head and the pressure
units selected by the user.
The sensitivity factors can be changed using the Sensitivity Tuning command in the
Head menu. In order to set these factors, you need a reference ion gauge installed in the
same vacuum system. The reading from the gauge is used to set the new sensitivity
factor for the RGA Head.
Note : The pressure limits you may enter will change if you have the Pressure Reduction
option enabled. If this option is enabled RGA lets you enter much higher pressure
values.
Spectrum Analysis
Mass spectrum analysis takes you one step beyond visual analysis and Library lookup
tables. RGA looks at the spectrum from 1 to 50 amu and uses a matrix inversion
technique to analyze the composition of the residual gas and approximate its
composition. Note that Analysis mode requires a minimum span of 1 to 50 amu. (The
span can be higher than 50.)
Background Data
This mode is helpful in providing the user with a clean baseline after the background
data gets subtracted from newly acquired scans. This utility is available in Analog
mode, Histogram mode, Table mode, and P vs T mode. In Analog mode and Histogram
mode the scan must be allowed to finish at the Stop mass before the data can be used as
background. Use the Stop at End command from the Scan menu (if in continuous scan
mode) to guarantee this condition.
In Analog and Histogram modes the full spectrum is subtracted from the newly
acquired spectrum. In Table and P vs T modes, only the last acquired partial
pressure of each mass get used as a background data. When a Table or P vs T
mode is split with Analog or Histogram mode AND background is enabled, the data
in the Table or P vs T graph is extracted from the Analog or Histogram graph and
NOT subtracted form its own previous data.