Instruction Manual IGM402 Hornet
InstruTech
Page 52
7.3
Effect of different gases on analog output
The following tables and explanation contains important information regarding the use of ionization and
convection gauges on gases other than N
2
/ Air. For both types of gauges, corrections must be applied to the
analog outputs.
7.3.1
Ion gauge analog output correction factors for selected gases
When using the 0-9 V Log-Linear analog output for the ion gauge, use the following steps to convert the analog
output to pressure:
A)
Refer to
section 6.1
and use the related equation to convert the voltage in your receiving instrument to
pressure. This pressure value is based on nitrogen gas.
B)
Apply the Gas Correction Factor for the particular gas you are using to the pressure value obtained in
step A. Use correction factors and example listed below:
Ion Gauge Gas Correction Factors for selected gases
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
Example
:
The gas in use is argon. Voltage output is 4 volts. Pressure unit is Torr.
P (nitrogen) = 10
(volts - 10)
P = 10
(4 - 10)
P = 1.0 x 10
-6
Torr (based on nitrogen)
Applying the Gas Correction Factor of 1.29 for argon listed in the table above,
P (argon)
=
𝟏.𝟎 ×𝟏𝟎
−𝟔
𝟏.𝟐𝟗
=
𝟕. 𝟕𝟓 × 𝟏𝟎
−𝟕
Torr true pressure of
argon
gas
The correction factor must be applied to the analog output over the entire pressure range measured by the ion
gauge.
