Stanford Research Systems RGA100, Operating Manual And Programming Reference

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6-38 Detection Control Commands
SRS Residual Gas Analyzer
Detection Control Commands
CA
Description : Calibrate All.
Echo: STATUS Error Byte.
Readjust the zero of the ion detector under the present detector settings, and
correct the internal scan parameters against small temperature fluctuations to
assure that the correct RF voltages (i.e. as specified by the last Peak Tuning
procedure) are programmed on the QMF rods as a funtion of mass.
In order to readjust the zero of its ion detector, the RGA measures the output of
its electrometer in the absence of input ion current and under the present detector
settings (i.e. noise floor and detector type). The current value obtained is stored
in internal memory as an offset correction factor that is automatically used by the
firmware to correct all ion currents measured (i.e. including those from single
mass and total pressure measurements) under the same detector settings.
Important:
x
Offset correction factors for all the possible combinations of detector settings
can be accumulated in the RGA’’s memory.
x
All offset correction factors are automatically cleared after a complete
recalibration (CL) of the electrometer is performed, and also when the
unit is turned off.
x
Use the CA command every time the detector settings are changed to values
that have not been used in a long time or that were never used since the unit
was turned on or recalibrated with the CL command.
x
The zero of the ion detector is also automatically readjusted at the beginning
of each analog and histogram scan so that the baseline is always centered
around zero.
In order to correct the mass axis against peak position shifts caused by small-
temperature fluctuations, the RGA characterizes the voltage output of the RF
driver’’s control circuit, and
recalculates its internal scan parameters to assure
that the correct RF levels (i.e. as specified by the last Peak Tuning procedure) are
programmed on the QMF rods as a funtion of mass.
Important: Use a complete Peak Tuning Procedure to correct the mass axis
calibration when large temperature fluctuations are suspected.
The
calibration procedure triggered by the CA command cannot correct the mass axis
against large temperature drifts that affect the response of the RF Driver to its
controlling voltage, or the relationship between mass and RF levels in the QMF
itself (i.e. due to changes in the QMF’’s physical dimensions).