SRS Labs QMS 100 Series, Руководство пользователя

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RGA Command Set 3-45
Technical Reference
The type of detector and noise-floor settings to be used by the measurement must be selected in advance
with the NF and HV commands.
The precision and duration of the measurement are totally determined by the NF parameter value. The
scan rates and signal-to-noise ratios for the different NF settings of the electrometer are listed in a table in
the Electrometer section of the “RGA Electronic Control Unit” chapter. The command execution time
includes some initial time spent waiting for the Quadrupole Mass Filter and the electrometer response to
settle. As usual, a compromise must be made between signal-to-noise and measurement time.
The ion current is expressed in the usual format: 4 byte long, 2's complement integer in units of 10
-16
A,
with Least Significant Byte transmitted first.
Important:
•
During a Single Mass Measurement the RGA performs a “ Miniscan”
around the mass requested, and the maximum current value measured is
sent out over RS232 . The scanning procedure, referred to as Peak-
Locking , is designed to measure peak currents for individual masses in a
mass spectrum without being affected by drifts in the mass-axis calibration.
The Miniscan covers a 0.6 amu range centered at the mass requested, and
selects the maximum current from 7 individual measurements performed at
0.1 amu mass increments.
•
The detector settings (i.e. type of detector and noise-floor setting) to be used
during the measurement must be selected in advance with the NF and HV
commands, otherwise, the measurements are performed with the detector
settings at the time the scan is triggered.
•
The ion detector can be zeroed, prior to the measurements, performing an
analog or histogram scan or using the CA command, under the same detector
settings. (An offset-correction factor is calculated and stored in memory that
it is then automatically used by the Miniscan procedure to correct all ion
currents measured). The CA command will also update the internal scan
parameters to assure that the correct RF levels (i.e. as specified by the last
Peak Tuning procedure) are programmed on the RF rods as a function of
mass during the Miniscan.
Parameters:
MR0: The RF/DC voltages are completely shut down and no measurement is performed (no ion current
is transmitted back to the host computer).
Use this command format at the end of a set of single mass measurements to make sure the RF/DC are
completely turned off.
MRparam, param:1 - M_MAX : A Miniscan is performed around the mass number selected by the
parameter and the maximum ion current is sent out over RS232.