Instruction Manual IGM402 Hornet
InstruTech
Page 48
7.1.1
Ion gauge display correction factors for selected gases
If you intend to use gases other than N
2
/ Air, you must manually apply a gas correction factor to the IG
displayed pressure measurement. The following table provides correction factors for some typical gas species.
To correct the display measurement, divide the displayed measured pressure by the correction factor for the gas
type being measured by your ionization gauge device:
Gas
Gas
Correction Factor
Gas
Gas
Correction Factor
He
0.18
H
2
O
1.12
Ne
0.30
NO
1.16
D
2
0.35
Ar
1.29
H
2
0.46
CO
2
1.42
N
2
1.00
Kr
1.94
Air
1.00
SF
6
2.50
O
2
1.01
Xe
2.87
CO
1.05
Hg
3.64
Ion Gauge Gas Correction Factors for selected gases
For example, if the gas in use is argon (Ar) and the ion gauge display indicates a measured pressure of 1.00E-6
Torr, from the table above for Ion Gauge Gas Correction Factors, the correction factor for argon is 1.29. Divide
the displayed pressure, 1.00E-6 Torr, by the correction factor, 1.29, to obtain the true pressure of argon gas in
your vacuum chamber: P (argon)
=
𝟏.𝟎 ×𝟏𝟎
−𝟔
𝟏.𝟐𝟗
=
𝟕. 𝟕𝟓 × 𝟏𝟎
−𝟕
Torr true pressure of
argon
gas
If you adjust the Sensitivity factor for your ion gauge to compensate the readout of pressure for a gas type other
than nitrogen, the displayed pressure readout for that device must be annotated to indicate that the displayed
pressure is for the gas type the readout is compensated for. In the above example, if the N
2
Sensitivity of the ion
gauge being used is 10 Torr
-1
(“10 per Torr”), the Sensitivity factor programmed during setup of the IGM402
for
could be set for 12.9 (~13) so that the pressure readout would indicate the true pressure of argon. Again, the
display line for that particular device pressure readout would require annotation so as to not conflict with the
notation “N
2
” following the “Unit” notation in the Pressure Measurement Screen.
7.2
Effects of different gases on convection gauge display
A thermal conductivity gauge senses heat loss, which depends on the thermal conductivity of the gas
surrounding the sensor. Since different gases, and mixtures, have different thermal conductivities, the indicated
pressure readings and outputs will also be different. InstruTech convection gauges (and most other thermal
gauges) are normally calibrated using dry nitrogen (N
2
). When a gas other than nitrogen is used, correction must
be made for the difference in thermal conductivity, between nitrogen (N
2
) and the gas in use. The charts and
tables on the following pages indicate how different gases affect the display and output from an InstruTech
convection gauge.
