SRS Labs QMS 100 Series, Руководство пользователя

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Programming the RGA ECU 3-17
Technical Reference
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 scale
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.
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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 that are present at the time the scan
is triggered.
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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.
Single Mass Measurement example
The following list of commands can be used to perform a single mass measurement at 28 amu. First, the
electron multiplier is turned off and the FC is connected to the electrometer, the noise floor is set to the
maximum averaging (best signal-to-noise ratio and longest measurement time), the zero of the detector
is readjusted, and the measurement is triggered. The single current value returned by this command is
the maximum current in the 28 +/-0.3 amu region of the mass spectrum, and must be corrected with a
sensitivity factor to obtain the actual partial pressure reading at mass 28.
Important : The RF/DC on the QMF are left at 28.3 amu at the end of this measurement, and the MR0
command can be used to turn them off.
Important : The CA command turns off the RF/DC at the end of its execution.
HV0 High Voltage CDEM = 0 Volts, FC detection enabled.
NF0 Maximum averaging (slowest scan rate) selected.
CA Readjust the zero of the detector for clean baseline and update the internal scan parameters.
MR28 Single measurement triggered @ 28 amu. A single current value is returned and the RF/DC
are left at 28.3 amu. Collect the 4 byte current value returned.(Use sensitivity factor to
convert it to pressure value.)
MR0 Turn off the RF/DC on the QMF rods when done measuring.
Single Mass Measurement programming tips
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Single mass measurements are very commonly used in program loops where several
different masses are monitored in a merry-go-round fashion and their partial pressures
displayed as a function of time.
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The outputs provided by a set of single mass measurements are often used in process
control programs to control alarms, analog and digital outputs, and relays. For example: