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Instruction Manual
Ion gauge display correction factors for selected gases
7.1.1
If you intend to use gases other than N
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
He
Ne
D
2
H
2
N
2
Air
O
2
CO
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) =
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
gauge being used is 10 Torr
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
" following the "Unit" notation in the Pressure Measurement Screen.
2
Effects of different gases on convection gauge display
7.2
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
be made for the difference in thermal conductivity, between nitrogen (N
tables on the following pages indicate how different gases affect the display and output from an InstruTech
convection gauge.
InstruTech
/ Air, you must manually apply a gas correction factor to the IG
2
Gas
Correction Factor
0.18
0.30
0.35
0.46
1.00
1.00
1.01
1.05
Ion Gauge Gas Correction Factors for selected gases
−��
��.�� ����
=
��.����
-1
("10 per Torr"), the Sensitivity factor programmed during setup of the IGM402 for
Gas
H
O
2
NO
Ar
CO
2
Kr
SF
6
Xe
Hg
−��
��. ���� × ����
Torr true pressure of argon gas
). When a gas other than nitrogen is used, correction must
2
IGM402 Hornet
Gas
Correction Factor
1.12
1.16
1.29
1.42
1.94
2.50
2.87
3.64
Sensitivity of the ion
2
) and the gas in use. The charts and
2
Page 48
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