Inficon VGC083A - IG over Pressure Shut down

tinb29e1-c (2019-10) VGC083A_B.om 29
In most general vacuum applications, the yttria coated iridium filament is the best
choice.
Yttria coated iridium filaments typically operate at a lower temperature than tung-
sten filaments and thus have a lower outgassing rate at UHV and lower chemical
reactivity with active gases. Yttria coated iridium filaments typically have a longer
operating life than tungsten filaments in clean applications.
The yttria coated filament can survive occasional accidental start attempts at at-
mosphere in air, but the overall life of the filament may be shortened during each
occurrence. Good vacuum practice is to use a separate pressure gauge such as
INFICON's PGE050 convection gauge to know when to turn on the ion gauge fila-
ment.
Typically, a bare tungsten filament is a better choice in those applications where an
yttria coated filament is quickly damaged due to the gas type in use. For example,
processes such as ion implantation may only use tungsten filaments. Be aware that
corrosive applications are hard on any filament and filament life will be shortened
while operating in such environments. Tungsten filaments are easily damaged by
exposure to air/oxygen during accidental system vents or if considerable quantities
of water vapor are outgassed during pump-down and bake-out. It is very important
to make sure the tungsten filament is turned off before bringing the chamber up to
atmosphere, especially if air is being used to vent the chamber. The use of pure N
2
gas is highly recommended to vent or purge your vacuum chamber. Testing has
shown that tungsten filaments can withstand limited high pressure excursions when
only N
2
is present.
Venting with air or other gases containing oxygen can damage the tungsten fila-
ments. If you try to turn on an ion gauge with tungsten filaments while it is sitting on
your desk exposed to room air, you will immediately damage or destroy the fila-
ment beyond repair.
Do not use another gauge to automatically turn off the ion gauge when the ion
gauge (IG) filament in use is constructed of tungsten (yttria coated filament is ok).
The response time of other gauges may not allow for timely turn off of the tungsten
filament leading to filament damage. Always turn off the IG filament manually be-
fore pressure is allowed to rise above 1.00 × 10
-3
Torr.
Both types of filaments will suffer eventual damage if operated at high pressures.
The type and amount of damage at high pressure is dependent upon the length of
operating time, the pressure and the gas present.
The VGC083 is provided with factory set default values for over pressure shut
down. The IG will shut off automatically should the pressure reach or rise above
the pressure shut down values shown below:
Factory set IG overpressure shut down values for BAG050 / 051 / 052 / 053
Emission Current
Overpressure Shut Down
Torr
mbar
Pa
100 µA (0.1 mA)
1.00 × 10
-3
1.33 × 10
-3
1.33 × 10
-1
4 mA
5.00 × 10
-4
6.65 × 10
-4
6.65 × 10
-2
10 mA
1.00 × 10
-4
1.33 × 10
-4
1.33 × 10
-2
Factory set IG overpressure shut down values for BAG055 Mini IG
Emission Current
Overpressure Shut Down
Torr
mbar
Pa
100 µA (0.1 mA)
5.00 × 10
-2
6.65 × 10
-2
6.65
4 mA
1.00 × 10
-3
1.33 × 10
-3
1.33 × 10
-1
Yttria coated iridium filament
Tungsten filament
NOTICE
NOTE
5.4 IG Over Pressure Shut
Down