Inficon Transpector XPR 3+ User Manual

4 - 14
Transpector XPR 3+ Operating Manual
The analyzer factor, A
b
, depends on the transmission and detection characteristics
of the analyzer, the Electron Multiplier gain (if the analyzer is so equipped), and the
basic sensitivity, as indicated in equation [4]:
[4]
Here, TF
b
is the transmission factor of the mass filter at mass b. The transmission
factor is the fraction of ions at mass b which pass through the mass filter, relative
to nitrogen ions at mass 28. Nominally, the transmission factor is equal to 28
divided by the mass of the ion, b.
The detection factor, DF
ab
, is equal to 1 for a Faraday Cup detector. For an Electron
Multiplier, the detection factor is a function of the mass of the ion and its chemical
nature, and is measured relative to that of a reference gas, typically nitrogen. In
general, as the mass ion increases, the Electron Multiplier detection factor
decreases.
The gain of the Electron Multiplier, G, measured at mass 28 for nitrogen, is the
Electron Multiplier output current divided by the Faraday mode output current,
under otherwise identical conditions. The multiplier gain is a strong function of the
high voltage applied.
The sensitivity of the instrument, S, is the ratio of Faraday mode ion current for a
given pressure of pure nitrogen measured at mass 28, and is typically expressed
in amps/Torr.
The overall relation between partial pressure and ion current, given in equation [5],
is quite general. The constants for this equation can be obtained from various
tables, but for the best accuracy, they should be measured for each instrument.
[5]
A brief discussion of each of the terms follows:
PP
a
. . . . . . . . . . . . . . . . . . . . . . . . . . Partial pressure of substance a (usually in
Torr).
FF
ab
. . . . . . . . . . . . . . . . . . . . . . . . . . Fragmentation factor, or fraction of total ion
current from substance a having mass b
(dimensionless; see Table 4-4 on page
4-11).
FF
N28
. . . . . . . . . . . . . . . . . . . . . . . . Fragmentation factor for N
2+
ions at 28 AMU
from nitrogen (dimensionless; typically
around 0.9).
A
a
1
TF
b
DF
ab
 G S
---------------------------------------------------=
PP
a
FF
N28
FF
ab
XF
ab
 TF
b
 DF
ab
 G S
-------------------------------------------------------------------------------------------



I
ab
=

Inficon Transpector XPR 3+ Specifications

General

Brand	Inficon
Model	Transpector XPR 3+
Category	Measuring Instruments
Language	English