Instruction Manual IGM402 Hornet
InstruTech
Page 53
7.3.2
IG + CG1 analog output correction factors for selected gases
When using the IG + CG1 analog output mode (Log-Linear 0.5 - 7 V, 0.5 V/decade) for gases other than N
2
/ Air,
the analog output is interpreted differently over two different pressure ranges as discussed below:
A)
Pressure range from the 1.0 x 10
-9
Torr to 1.0E-03 Torr:
Use the information and equation described in
section 6.2
and the correction factors listed in
section
7.3.2.1
below to determine pressure from the voltage for selected gases (ion gauge range).
B)
Pressure range from 1.0E-03 to 1,000 Torr:
Use the correction factors listed in
section 7.3.2.2
below to determine pressure from the voltage for
selected gases (convection gauge range).
7.3.2.1
IG + CG1 analog output correction factors - Ion gauge range
A)
When using the IG + CG1 analog output mode (Log-Linear 0.5 - 7 V, 0.5 V/decade) for gases other than
N
2
/ Air, use the following steps to convert the analog output to pressure when operating in the pressure
range of 1.0 x 10
-9
Torr to 1.0E-03 Torr.
B)
Refer to
section 6.2
and related equation to convert the voltage in your receiving instrument to
pressure. This pressure value is based on nitrogen.
C)
Apply the sensitivity 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. Output voltage is 3 volts. Pressure unit is Torr.
P (nitrogen) =
10
𝑣𝑜𝑙𝑡𝑠−5.5
0.5
= 10
(3.0 – 5.5) / (0.5)
, P =
1 × 10
−5
Torr (based on nitrogen)
P (argon) =
𝟏 ×𝟏𝟎
−𝟓
𝟏.𝟐𝟗
=
𝟕. 𝟕𝟓 × 𝟏𝟎
−𝟔
Torr true pressure of
argon
gas
The same correction factor must be applied over the entire pressure range as measured by the ion gauge.
