Stanford Research Systems RGA100, Operating Manual And Programming Reference

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Programming the RGA Head 6-17
SRS Residual Gas Analyzer
Important:
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The detector’’s zero and the internal scan parameters are checked and corrected at the
beginning of each scan resulting in a slight delay before the scan actually starts.
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The measurements are performed with the detector that is active at the time the scan
is triggered.
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A Total Pressure measurement is performed at the end of each scan and transmitted
out to the host computer. In the event where the CDEM is turned on, the total
pressure returned from the head is 0.00. (Please see AP and TP Commands).
Setting up an analog scan
The following list of commands sets a scanning range of 10 to 150 amu, the fastest scan
rate (minimum averaging), 0.1 amu steps, and, after checking the number of currents to
be measured per scan (not including total pressure), it triggers 10 scans under those
conditions. Each one of the 10 scans transmits 1401 scan currents and one total pressure
current, and each current is 4 bytes long.
MI10 Initial mass = 10 amu.
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
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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.
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Notice that MI and MF are shared by analog and histogram scans.
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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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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 head 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.