SRS Labs QMS 100 Series, Руководство пользователя

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Glossary
SRS QMS Gas Analyzer
cannot be differentiated from each other with most mass spectrometers. Note: Mass
spectrometers do not actually measure the molecular mass directly, but rather the mass-to-charge
ratio of the ions. For singly charged ions, the mass to charge ratio is numerically equal to the mass
of the ion in atomic mass units (amu).
Minimum Detectable Partial Pressure change (MDPP). The partial pressure change
corresponding to the smallest signal change which can be distinguished from noise. A common
prescription is,
∆
p
min
=
σ
/S
g
, where
σ
is the noise and S
g
is the partial pressure sensitivity for the
gas being measured.
Noise . Random fluctuation in the output signal unrelated to a change in the partial pressure of the gas
from which the signal is derived. The appropriate measure of noise is the standard deviation
σ
N
of
N independent determinations of the average output signal obtained at constant partial pressure.
Open Ion Source (Also Nude Ion Source). An ionizer with electrodes of high transparency to gases.
Outgassing . The evolution of gas molecules from the internal wall surfaces of the vacuum system.
Parent ion . An ion of the same mass as that of the original parent molecule.
Partial Pressure Analyzer (abbreviation: PPA). A compact mass spectrometer used to analyze the
residual gas composition in a vacuum system.
Partial Pressure . The pressure of a designated component of a gaseous mixture within a system as it is
exerted on the chamber walls. The sum of the partial pressures of all the kinds of gases gives the
total pressure.
Peak height (also peak intensity). The maximum ion signal developed in the RGA for a given mass-
to-charge ratio peak.
Peak width (
∆ ∆
M
v%
). The difference between the mass-to-charge ratio values on either side of a mass
peak at which the signal has dropped to v% of the peak height, H. See also Resolution.
Principal mass peak. The most intense peak in the fragmentation pattern of any molecule.
Probe (also RGA Probe). Quadrupole mass spectrometer sensor consisting of an ionizer, a mass
analyzer and a detector (Faraday cup or optional electron multiplier).
QMS - quadrupole mass spectrometer
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.