Stanford Research Systems RGA100, Руководство по эксплуатации и программированию

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Peak Tuning Procedure 7-9
SRS Residual Gas Analyzer
DI = DI
0
-
'
m * 28
Notes:
x
The new DI value must fall within the acceptable parameter range of the DI
command.
x
A change in DI affects the width of all the peaks in the spectrum.
x
A decrease in DI results in broader peaks at a rate of 0.036 amu per bit removed.
High Mass Peak Width Adjustment : To modify the high mass peak width by an
amount
'
m amus, modify the value of DS from its original value DS
0
to:
DS = DS
0
- 28 * (
'
m) / m
0
Notes:
x
The new DS value must fall within the acceptable parameter range of the DS
command.
x
Modifying DS affects the width of peaks at the higher end of the spectrum. An
increase in DS results in the peaks getting sharper, and a decrease in DS results in the
peaks getting broader
x
The effect is more significant at the higher masses and that is why we do this
adjustment second after the width has already been modified by the change in DI.
x
If the mass-to-charge ratio of the low mass gas is real low this adjustment will have a
small effect on the width of its peak.
Iterations: In most cases it will be necessary to repeat the two width adjustments one or
two more times until both low and high mass peaks show the desired widths.
Note: Changes in the peak positions will also be observed, at a rate of -0.40 amu per amu
of increase in peak width, and a Peak Position Tuning procedure will be needed to put the
peak positions back where they belong.
Important : The Peak Width Tuning Procedure can be used to adjust the resolution of the
RGA to the ultimate theoretical limit of the mass filter. See the Quadrupole Mass Filter
section of the RGA Probe chapter of this manual for details on that limit.
Temperature effects on the mass scale calibration:
As the temperature of the RGA Head changes two different effects affect the calibration
of the mass scale:
x
For small temperature changes : Drift in the voltage output of the RF Driver that
controls the RF power supply can cause the mass peaks to shift their position in the
mass spectrum. In order to correct against this effect, the RF driver output is checked
at the beginning of each analog and histogram scan at 0 and 128 amu. The internal
calibration parameters, used by the firmware to step the RF during scans, are updated
so that the control levels specified by the RI (0 amu) and RS (128 amu) parameter
values are correctly set at the present temperature.