Stanford Research Systems RGA100, Operating Manual And Programming Reference

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Ionizer Control Commands 6-35
SRS Residual Gas Analyzer
A firmware-driven ““ Filament Protection Mode”” monitors the performance of
the filament while it is emitting electrons and if a problem is detected at any time,
the heater is immediately shut down and the problem is reported through the
error bytes and the error LED’’s (see below).
WARNING: The pressure in the chamber must be under 10-4 Torr before
turning the filament on!
Important:
x
The repeller grid and the focus plate are only biased while the filament is
emitting electrons.
x
In order to protect the filament, the emission current is defaulted to zero
when the RGA is turned on.
x
The CDEM is turned off by any overpressure that also shuts down the
filament.
Parameters :
FL0.00: The filament is turned off and the repeller grid and the focus plate are
grounded.
FLparam, param: 0.02-3.50 : The parameter is the requested Electron
Emission Current in units of mA. The repeller grid and the focus plate are biased,
and the filament’’s heater is activated until the requested electron current is
achieved.
FL* : The command is excecuted using the default parameter value.
Default: 1.00 mA
FL? : Returns over RS232 the value of Electron Emission Current (in mA)
actually flowing through the ionizer.
Important: The number returned by the query command will always be very
close, but rarely identical, to the current value set with the FLparam command.
The difference observed will never /-0.02 mA. The value returned is the
actual electron current circulating through the ionizer as internally calculated by
the RGA head. The discrepancy is due to the finite resolution of the digital-to-
analog converters used to program the ionizer's emission current.
Error Checking:
The absence of a parameter (i. e. FL) is treated as a bad-parameter error.
The STATUS byte is echoed to the host computer at the end of the command
excecution, and it should be checked to determine whether the requested electron
emission current was succesfully established. If Bit 1 of STATUS is found set,
FIL_ERR should be immediately checked to identify the specific problem (See
EF? command in the Error Reporting Commands list). It is good practice to
attempt the command a second time before declaring a hardware problem. Once