Stanford Research Systems RGA100, Operating Manual And Programming Reference

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Peak Tuning Procedure 7-5
SRS Residual Gas Analyzer
On-line Help Files included with the program for details.
Note to Supervisors: A calibration disable jumper (JP100) can be configured to block
any attempt to change the value of the mass filter settings in the RGA Head. The jumper
is located on the top electronics board of the ECU box, next to the microprocessor chip
(i.e. biggest component on the board), and its two settings are clearly indicated as CAL
DIS and CAL EN.
Supervisors may use this feature to prevent accidental changes in
the calibration parameters by inexperienced operators. Peak tuning is completely
disabled when the jumper is configured to the CAL DIS setting.
Tip: Virtually every vacuum system will have detectable amounts of hydrogen (2 amu),
water (18 amu), carbon monoxide (28 amu) and carbon dioxide (44 amu). Become
familiar with these species and their fragmentation patterns, and use their peaks to
quickly verify the correct performance of the instrument (i.e. mass scale calibration and
mass resolution) while operating the RGA.
General Procedure
Peak tuning is a simple procedure that requires the introduction of two known gases into
the vacuum system. A low mass gas (1-20 amu recommended) is used to adjust the low
end of the mass axis, a high mass gas, with a mass-to-charge ratio close to the upper limit
of the instrument’’s mass range, is used to adjust the high end of the mass scale.
Several analog scans are performed on the sample and the peak positions and widths are
checked and adjusted as necessary. Changes in resolution affect the sensitivity of the
RGA, and a Sensistivity tuning procedure should always be performed at the end of the
peak tuning process.
The entire procedure can be carried out with the help of the Peak Tuning command (Head
Menu) of RGA Windows. The program guides you through the calibration procedure and
automatically updates the Peak Tuning Parameters in the RGA Head based on the results
of the calibration.
The overall adjustment procedure is very simple and must follow the order described
below:
1. Low mass peak position adjustment
2. High mass peak position adjustment
3. Repeat 1 & 2 in that order one or two more times until no more changes in peak
positions are observed.
4. Low mass resolution adjustment
5. High mass resolution adjustment
6. Repeat 4 &5 in that order until no more changes in peak width are observed.
7. Repeat 1 & 2 in that order one or two more times in the case steps 4 & 5 caused
changes in peak positions.
Important : Collect a fresh analog scan for each step. The peak positions are adjusted
such that all peaks throughout the scanning range of the RGA fall /- 0.25 amu of