Stanford Research Systems RGA100, Operating Manual And Programming Reference

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14 Appendix D
SRS Residual Gas Analyzer
Concepts from the example:
Within LabVIEW, view the block diagram of SRSRGAa Simple Analog (press Control-E if you are
already looking at the front panel of the VI). The next figure shows this block diagram.
Note that this block diagram is very similar to the Simple Table block diagram. Again, only six VIs are
used. All the VIs in gray are taken from the operations layer, while the only one that is not is the general
SRSRGA Error handler VI. Just as in the communications layer example, you can see that an error
cluster is propagated through the six VIs. However, rather than propagating the SRSRGA VISA session
explicitly, the session is propagated by referring to its reference number (or refnum). By double-clicking
on the sub-VIs that appear to the right of the Open VI, you will see that each VI takes the refnum as input,
then passes it to SRSRGAo Get Session. This VI accesses the serial communications session referred to
by the SRSRGA refnum, and sends commands or receives data from that session. By using the
operations level, you don’’t have to worry about dealing with the VISA session directly; the VIs in this
layer will handle that for you.
In this VI, an array of all the points in the scan is created beforehand and each point initialized as ““not a
number””. This is different from the previous example of Simple Table scanning, where the points are
simply plotted as they are read in. In Simple Histogram (and Analog) the initialized array changes in the
ordinate (pressure) as new values are read in, but the abscissa (the mass range) always stays the same.
Also, rather than using a multiple number of milliseconds in the while loop, a fixed delay of 250
milliseconds is used. Very tight while loops often put stress on a multi-threaded application or operating
system. This slight delay helps guard against problems stemming from having no delay in the execution
of the while loop.
Applications Layer VIs
What are the applications layer VIs?
The applications layer is built upon the VIs in the operations layer. In the previous section, we discussed
the use of several operations layer VIs in three application examples (simple analog, histogram, and
table). In this section, we discuss using a fully developed application that encompasses setups for the
RGA hardware, scanning parameters, and datalogging.