Stanford Research Systems RGA100, Operating Manual And Programming Reference

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Glossary of Terms
SRS Residual Gas Analyzer
5
Probe (also RGA Probe). Quadrupole mass spectrometer sensor consisting of an ionizer,
a mass analyzer and a detector (Farday cup or optional electron multiplier).
Repeller (Ionizer Component). The repeller grid cage completely encloses the ionizer,
is biased negative relative to the filament, and prevents the loss of electrons from the ion
source.
Residual Gas Analyzer (abbreviation: RGA). A compact mass spectrometer used to
analyze the residual gas composition in a vacuum system (same as Partial Pressure
Analyzer).
Resolution, or Absolute Resolution,
'
M
10%
. The width
'
M of the pass band of the
filter, defined as the full width at which the ion current falls down to 10% of the
maximum value. In mass-to-charge ratio units. See also Peak width.
Resolving Power: R= M/
'
M
10%
: Ratio between a particular mass-to-charge ratio M and
the resolution,
'
M
10%
, at that mass. Dimensionless ratio.
RGA. Abbreviation for Residual Gas Analyzer.
RGA Cover Nipple. CF Nipple that covers the RGA Probe.
Scan Speed (mass spectrometer). The speed at which the RGA scans through a range of
succesive mass numbers.
Scanning. The procedure of continuously changing the mass tuning of the quadrupole
mass spectrometer to bring successive mass numbers into tune.
Sensitivity.
Partial Pressure :
The partial pressure sensitivity of the RGA to a gas g,
S
g
, is defined as the ratio of the
change
(H-H
0
)
in principal mass peak height to the corresponding change
(P-P
0
)
in
total pressure due to a change in partial pressure of the particular gas species.
H
0
and
P
0
are background values.
S
g
= (H-H
0
) / (P-P
0
)
The units of
S
g
are of ion current per unit pressure (amp/Torr, for example).
Total Pressure :
The total pressure sensitivity of the RGA to a gas g, is defined similarly as the ratio of the
change
(H-H
0
)
in total ion current to the corresponding change
(P-P
0
)
in total pressure
due to a change in partial pressure of the particular gas species.
H
0
and
P
0
are
background values.