Inficon Transpector MPH Operating Manual page 78

The overall relation between partial pressure and ion current, given in
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.
PP =
a
Where:
PP
a
FF
ab
FF
N28
XF
TF
DF
G. . . . . . . . . . . . . . . . . . . . . . . . . Electron Multiplier gain for nitrogen ions at 28
S . . . . . . . . . . . . . . . . . . . . . . . . . sensitivity of instrument to nitrogen, the ion
I
ab
4 - 13

--------------------------------------------------------------------------------------- -

 
FF XF

ab ab
. . . . . . . . . . . . . . . . . . . . . . . partial pressure of substance a (usually in
. . . . . . . . . . . . . . . . . . . . . . . fragmentation factor, or fraction of total ion
. . . . . . . . . . . . . . . . . . . . . fragmentation factor for N
. . . . . . . . . . . . . . . . . . . . . . . ionization probability of substance a relative
a
. . . . . . . . . . . . . . . . . . . . . . . transmission factor, the fraction of total ions
b
. . . . . . . . . . . . . . . . . . . . . . detection factor for mass b ions from
ab
. . . . . . . . . . . . . . . . . . . . . . . . ion current of mass peak b resulting from
FF
N28
 
TF DF G
b ab
Torr)
current from substance a having mass b
(dimensionless; see
from nitrogen (dimensionless; typically
around 0.9)
to nitrogen; approximately the same as the
relative ion gauge sensitivity as shown in
(dimensionless)
at mass b which pass through the mass filter,
relative to ions with a mass of 28 AMU;
nominally, T
FM
substance a, relative to nitrogen at 28 AMU;
assumed to be 1.00 for Faraday detectors,
but varies for Electron Multiplier detectors
(dimensionless)
AMU (dimensionless; set equal to 1 for
a Faraday Cup detector)
current at 28 AMU per unit of nitrogen partial
pressure (usually in amps/Torr)
substance a (in amps; assumes that there are
no other substances present which
contribute significantly to the total current at
mass peak b)
Transpector MPH Operating Manual
equation


I

ab

S

Table 4-4 on page
ions at 28 AMU
2+
= 28 / M (dimensionless)
[5],
[5]
4-10)