© Arun Microelectronics Ltd 2020. All rights reserved
Page 26
9.
Degassing
Read this entire section before attempting degas. Degas is required in UHV systems periodically. It is not desirable to
degas at high vacuum and above as this could damage the gauge or affect other operations in the vacuum chamber.
Degas increases the emission current and grid voltage so that the grid is heated to drive off adsorbed gas. The degas
power should be increased slowly to allow the gas evolved to be pumped away. If power is increased too rapidly plasma
will be produced, which will short the grid to the filament or ground. The instrument will detect this and degas will be
aborted to protect the gauge and instrument.
The instrument only allows degas to start:
•
When a valid password has been entered (if password use is enabled).
•
If the gauge has run in emission for at least 5 continuous minutes in the preceding 30 minutes.
If any condition prevents degas starting then
“
Degas Denied
”
will be displayed. Move the Function Switch to OFF.
If the Ion Gauge is in emission when degas is selected, emission will not be interrupted (unless degas is denied) and degas
will seamlessly start when the mode has been selected. If the Ion Gauge is not in emission when degas is selected, emission
is run automatically at 0.5 mA and then 5 mA for a few seconds before degas power is applied.
A fixed degas overpressure trip (1E
–
5 mBar) is active for a few seconds at 5 mA. Degas is aborted if the pressure exceeds
that level. In all modes, degas power is changed in 2.5 W steps.
In Program and Quick modes, the pressure can continue to be read during degas by returning the Function Switch to the
corresponding IG position. If the Function Switch is left in the IG position when degas finishes, normal emission will resume
seamlessly. If the Function Switch is left in the DEGAS position when degas finishes, emission will cease.
Relay operations are suspended during degas.
Move the Function Switch to the DEGAS position to select the
required mode. Select Manual, Program or Quick with
△
or
▽
and confirm by pressing ENT.
In program or quick modes, the grid power is increased
automatically. Use Manual Degas to derive safe rates of power
increase and maximum power to set up the other modes in
SETUP
→
DEGAS
Once UHV has been established most systems will only require
an occasional Quick Degas.
Summary of Contents for NGC3
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