Experimental Physics and Industrial Control System
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We've used LabVIEW for quite some time for a variety of tasks on the
PNC-CAT beamlines at the APS. For our primary interface we use a LabVIEW
application that is primarily a CA client for iocs running modified
versions of the synApps distribution. It also provides additional
client-side control such as scripting-like automation of tasks, hiding of
PV names from users by use of user-defined names for PVs, etc. Non-epics
devices are integrated into the same user interface. CA uses the SCA
library for Win32 from Chris Timossi at LBNL, and in my opinion functions
quite well. Users typically have quite a few front panels open controlling
several motors, scalers, scans, multielement detectors, and so on,
connecting to dozens if not hundreds of PVs, and LabVIEW functions
adequately in terms of performance and stability. The application does take
quite a bit of RAM, but 512MB is sufficient for our beamline computers.
It's flexible enough that we use the same executable for both beamlines and
use ini files at run time to specify PV names and control which modules are
loaded to account for hardware differences. We've generally had quite
positive comments from users. Many are familiar w/ LabVIEW both in terms of
use and program development, and we've collaborated w/ users to develop
tomography and surface diffraction applications.
Another LabVIEW application provides feedback control of our
monochromator, using the NI PID toolkit. It runs two feedback channels at
500Hz with performance up to our requirements. We haven't tested it at
higher speeds but I don't see a reason it couldn't be pushed faster.
Non-epics devices at the beamline are controlled by a server using the
NI datasocket protocol. It performs well enough but an epics interface
would be more convenient to integrate scanning of positioners (e.g. slit
positions), and recording of detectors during scans. I've looked into the
ActiveX epics interface others have mentioned but haven't gotten to the
point of trying to use it.
In terms of future needs on the client end, LabVIEW w/ SCA/Win32 works
about as well as I would want. At the server end, as I mentioned, a CA
interface would be nice as far as integrating positioners and detectors
controlled by LabVIEW into our beamline software. The main requirement I
can think of for a future CA interface is that it be more scalable than
datasocket. With datasocket, one has to wait for client writes to
individual datasocket items with a separate element on the diagram for each
datasocket item. This makes it difficult to scale up to a large number of
datasocket items. I've resorted to combining individual related variables
into an array or LabVIEW "cluster" and sending/receiving the whole thing at
once even if only a single element changes.
dale brewe
At 10:11 AM 3/8/2004, Ned Arnold wrote:
I recently had a discussion with the Product Manager of LabView
Realtime/Embedded about possibly implementing a tightly-coupled EPICS
interface to LabView. They have heard alot about EPICS from their
customers and would like to investigate what would be involved in
providing this capability in an integrated way.
The first question for us to answer is "what do we want?". So, I would
like to hear people's experience with the EPICS/LabView interfaces that
are currently available. I know of two major ones:
- Active-X interfaces (for clients and server)
- Shared-memory interface to standard EPICS records (3.14)
Please contribute your experiences, comments, ideas, wishes, etc with
these solutions or let us know of any others that have been done. For
those of you familiar with LabView, what other
capabilities/features/performance requirements would you like to see?
The goal would be to develop a list of requirements for the
"out-of-the-box" LabView/EPICS solution.
Please reply by March 12.
Ned
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Dale L. Brewe PNC-CAT/U. of Washington
ph: 630 252 0582 fax: 630 252 0580
Mail:
Argonne National Laboratory
Bldg 435E sector 20
9700 S. Cass Ave.
Argonne, IL 60439
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
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