SRS Labs QMS 100 Series, User Manual

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3-14 Programming the RGA ECU
SRS QMS Gas Analyzer
MF150 Final mass = 150 amu.
NF7 Fastest scan rate selected.
SA10 Steps/amu = 10.
AP? Analog Points query. The number 1401 is echoed. Add one for total pressure.
SC10 Analog Scan trigger: 10 scans are generated and transmitted.
Analog Scan Programming Tips
•
It is good programming practice to follow each command that sets a parameter with a query
of the parameter setting. For example, the first command in the list should be followed by a
MI?, and a number 10 should be echoed by the RGA.
•
Notice that MI and MF are shared by analog and histogram scans.
•
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!
•
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 by the RGA ECU 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 lines. 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.
•
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
finish transmitting it 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 SC1 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.
•
Perform a complete Peak Tuning procedure on the RGA ECU if the peaks in the
spectrum do not appear at their correct mass values (Consult the Peak Tuning section in the
RGA Tuning chapter).
Setting up Histogram Scans
A Histogram (Bar Mode) Scan consists of a succession of individual single mass measurements over a
pre-specified mass range. A single value is used to represent the peak heights at each integer mass
within the range. Histogram scanning is one of the most commonly used modes of operation for the
RGA. Its two main advantages are a faster scan rate than analog scans, and a reduced amount of data
being exchanged during the scan.