28 tinb29e1-c (2019-10) VGC083A_B.om
5 Operation - IG and CG
When used with BAG050 / 051 /052 / 053 nude/glass IG 100 µA (0.1 mA), 4 mA,
and 10 mA are available settings of emission current for the hot cathode ion gauge.
When used with BAG055 Mini IG 100 µA (0.1 mA) and 4 mA are available settings
of emission current for the hot cathode ion gauge.
1) In clean applications and when operating at higher pressure ranges
(5.00 × 10
-6
Torr to 1.00 × 10
-3
Torr) the 100 µA emission setting is preferred.
2) At lower operating pressures (1.00 × 10
-9
Torr to 5.00 × 10
-4
Torr) the 4 mA
emission setting should be used.
3) When using the nude or glass IG
many vacuum measurement equipment users
prefer to use the 10 mA emission current setting when making measurements
in the UHV pressure regime (below 1.00 × 10
-8
to 10
-11
Torr).
4) When using a diffusion pump or other pumps that use fluids, there is a possibili-
ty of the pump oil vapors entering the IG head. These vapors may form an
insulator on the internal components of the head which can lead to instability or
failure in controlling the emission. In this case, 4 mA and 10 mA emission
current may provide improved operating lifetime and measurement perfor-
mance.
5) The emission current can also be set to automatically switch between 100 μA,
4 mA and 10 mA. This results in optimal and stable pressure readings over the
entire measurement range from low to high vacuum. For example, if an applica-
tion requires that pressure measurements be performed by the ion gauge from
pressures lower than
VGC083A: 5.00 × 10
-6
Torr up to 1.00 × 10
-3
Torr
VGC083B: 1.00 × 10
-6
Torr up to 1.00 × 10
-3
Torr,
then the user may want to consider selecting the auto switching feature of the
emission current.
Electron bombardment degas (VC083A) or I
2
R resistive degas (VGC083B) is used
to rid a hot cathode ion gauge sensor of adsorbed gas. The intervals at which de-
gas should be applied vary for each application. The low pressure measurement
performance of the head will normally improve after each degassing cycle.
• Degas can only be applied while the filament is turned on and operating.
• Ensure that the vacuum pressure is at or less than 5.00 × 10
-5
Torr before
attempting to initiate degas.
• Degas will automatically turn off after 10 minutes when using factory default
settings. Degas can be programmed for duration of 2 to 30 minutes.
• The VGC083 will continue to measure approximate pressure while degas is in
progress.
• Degas will automatically turn off if the pressure exceeds 1.00 × 10
-4
Torr during
the degas cycle when using the BAG050 / 051 / 052 / 053 IG, or 4.00 × 10
-3
when using the BAG055 Mini IG but the filament will remain turned on.
• Degas can be interrupted by turning the IG filament off.
The choice of which filament to use is primarily dependent upon the process and
process gases the ion gauge will be used with. For general vacuum applications,
dual yttria coated filaments are offered for use with air and inert gases such as N
2
,
argon, etc. Optional dual tungsten filaments are available for use with gases that
are not compatible with yttria coated iridium filaments.
5.3 IG Filament Material
Selection / Venting the
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