Inficon Transpector SPS Operating Manual page 88

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 =
PP
a
FF
ab
(dimensionless; see
FF
N28
around 0.9).
XF
relative ion gauge sensitivity as shown in (dimensionless).
TF
b
relative to ions with a mass of 28 AMU; nominally,
T
FM
DF
assumed to be 1.00 for Faraday detectors, but varies for EM detectors (dimensionless).
G
= EM gain for nitrogen ions at 28 AMU (dimensionless; set equal to 1 for a Faraday Cup
detector).
S
= sensitivity of instrument to nitrogen, the ion current at 28 AMU per unit of nitrogen partial
pressure (usually in A/Torr).
I
ab
In amps; assumes that there are no other substances present which contribute significantly to
the total current at mass peak (b).
5 – 31
FF

------------------------------------------------------------------------------------------ -

 
FF ab XF ab TF b

= partial pressure of substance a (usually in Torr).
= fragmentation factor, or fraction of total ion current from substance a having mass b
Table 5-8 on page
= fragmentation factor for N
= ionization probability of substance a relative to nitrogen; approximately the same as the
a
= transmission factor, the fraction of total ions at mass b which pass through the mass filter,
= 28 / M (dimensionless).
= detection factor for mass (b) ions from substance (a), relative to nitrogen at 28 AMU;
a
b
= ion current of mass peak (b) resulting from substance (a)

N28

  
DF ab G S

5-28).
ions at 28 AMU from nitrogen (dimensionless; typically
2+
Transpector SPS Operating Manual
equation

I ab
[8],
[8]