SRS Labs QMS 100 Series, Руководство пользователя

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3-16 Programming the RGA ECU
SRS QMS Gas Analyzer
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Any command sent to the RGA during scanning will immediately halt the scanning action
and clear the RGA’s transmit buffer. Remember to also clear the computer’s receive buffer
to reset the communications. The new command responsible for stopping the scan will be
executed!
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It is good practice to perform an analog scan before triggering a large set of histograms to
assure the correct peak tuning (i.e. correct peak locations and widths) of the quadrupole
mass filter. Perform a complete Peak Tuning Procedure as described in the RGA Tuning
chapter of this manual if significant shifts in the peak locations are observed.
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The RGA has the ability to store a complete scan in its output buffer. The scan remains in
memory until all the data is transmitted out to the host computer over RS232. As a result of
the high acquisition rate of the RGA there might be a delay between the time at which the
data is collected and the time at which a complete spectrum is displayed by the host
computer. The time lag between data acquisition and display depends on a large number of
factors including the scan rate (NF setting) of the RGA, the host computer’s processing
speed, and the amount of handshaking activity over the RS232 line. As computers get
faster, they will be able to catch up with the RGA data acquisition speed and this problem
will no longer need any consideration.
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Before a new scan starts, the RGA checks its internal memory to make sure that no data
from any previous scan is pending to be transmitted. If data is still pending, the RGA must
first finish transmitting the stored data before the new scan can start. This process may result
in a delay from the time the scan trigger is received to the time it actually starts. Using the
HS1 command and waiting until the whole scan data stream is transmitted back to the host
computer will minimize the problems that are associated to this feature.
Single Mass Measurements
Single mass measurements are triggered with the MR command. The parameter is the integer mass
number (mass-to-charge ratio in amu units) at which the measurement is performed.
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 Electronics 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:
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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