Stanford Research Systems RGA100, Operating Manual And Programming Reference

Page: 117 / 362

Programming the RGA Head 6-13
SRS Residual Gas Analyzer
Programming the Ionizer
Positive ions are produced in the ionizer by bombarding residual gas molecules with
electrons derived from a heated filament. The operational parameters that affect the
efficiency of the ionizer are: electron energy, ion energy, electron emission current, and
focusing voltage. The
Ionizer Control Commands program all the ionizer voltages, turn
the filament on/off, and Degas the ionizer. The STATUS byte is transmitted at the end of
their execution.
Important : Remember that the Repeller grid and the focus plate are only biased while
the filament is emitting electrons.
Setting the ionizer parameters
The following list of commands will set the electron energy to 70 eV, ion energy to high
(12eV), focus voltage to -100V and it will then turn the filament on with an emission
current setting of 1.0 mA. It is a typical example of the set of commands sent to the RGA
while programming the ionizer.
EE70 Electron Energy = 70 eV. Echoes the STATUS Byte.
IE1
Ion Energy = high (12eV). Echoes the STATUS Byte.
VF100 Focus Voltage= -100V. Echoes the STATUS Byte.
FL1.0 Filament emission = 1 mA and turn filament on. Echoes the STATUS
Byte.
Ionizer Programming Tips
x
It is possible to trigger scans and single mass measurements if the filament is not
turned on.
x
Make sure the pressure is under 10
-4
Torr before turning the filament on or degassing.
x
Whenever possible replace a Degas procedure with a thorough Probe Bakeout (See
RGA Maintenance Chapter for details). Keep the degas time to the minimum value
that will get the job done. Frequent degassing compromises the lifetime of the
filament.
x
The filament is frequently tested by the CPU while it is turned on. Consult the
Filament, Leak and Burnt LED’’s after activation for immediate status feedback.
x
Wait for the STATUS byte to be returned between commands and check it every
time for possible errors.
x
In cases were a hardware error is reported retry the command one more time before
declaring a hardware problem.
x
Default parameter settings are available for all the Ionizer Control commands
x
Use the FL0 command to turn off the filament.