SRS Labs QMS 100 Series, Руководство пользователя

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Calibration 3-9
User’s Manual
The Peak Tuning procedures described in this section allow the user to calibrate the mass scale and the
resolution,
∆
m
10%
, of the mass spectrometer. The RGA has a very solid design and this type of tuning
procedures should rarely be needed.
WARNINGS
The peak tuning procedures should be performed by qualified personnel only. A mistuned
RGA Head will give Erroneous Readings until it is retuned properly.
Peak Tuning should only be attempted after the unit has been warmed up (with the filament
on and under typical operating conditions) for at least a one hour.
Peak Tuning requires a mixture of gases whose mass spectra is well known. In general, a two gas
mixture, one with low mass peaks and one with high mass peaks, is sufficient. The sample is introduced
into the vacuum, and the quadrupole mass filter parameters, referred to as Peak Tuning parameters, are
adjusted based on the sample analog spectra. The mass scale is adjusted so that all peaks are displayed
at their correct mass-to-charge values, and the peak widths,
∆
m
10%
, are adjusted to unity (or smaller)
values. The two tuning procedures are referred to as Peak Position and Peak Width Tuning,
respectively.
Note: A mixture of He, Ar, Kr and Xe inert gases is used at SRS to Peak Tune the RGA’s. The
resolution is adjusted to 1 amu and peak tuning parameters are saved into the RGA ECU before
shipping. The inert gases cover a broad spectral range, and being inert they do not interact with the
RGA probe and do not contribute to its aging.
Peak tuning can be easily performed with RGA Windows using the Peak Tuning command of the Head
Menu. The program provides password protection for locking out the Peak Tuning Parameters so that
casual users cannot alter the mass scale calibration or the spectrometer’s resolution.
An extra copy of the tuning parameters determined at the factory for the mass filter is saved in the RGA
Head before shipping, and those values can be retrieved at any time in case they are necessary. Consult
the RGA Windows chapter of this manual or the RGA 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.