EPS / PLC

['Dr. Pete Jemian' <jemian@unicat-sun.mrl.uiuc.edu>]

From the SRI-CAT presentation at the Beam Line Controls meeting this
month, their EPS system sounds very similar to UNICAT's, including the
relative cost.  The cost depends on how many fancy things one wants to
have.  If the I/O can be kept to simple boolean decisions, then cost is
minimized and execution speed is maximized.  To do this, UNICAT is
using process controllers (Love Series 1600).  With the Love
controllers, set points are controlled on the controller and do not
need to be in the PLC program.  The Love controller has a relay output
that we're using to signal the PLC whether GOOD or BAD.  The analog
value of the Love controller (termperature, voltage, or current) is
communicated along a RS-485 bus to EPICS.  The interconnect between
the Love controllers and EPICS is:
Love1 == Love2 == Love3 -> RS-485 -> IP-485 -> MVME 162 (HiDEOS) -> 
                                      VME backplane -> MVME 167 (EPICS)
The RS-485 bus with the Love controllers will take up to 254 +/- 1 (?)
controllers, individually addressed through a single RS-485 port.
UNICAT will need lees than 10% of that capacity for one beam line.
The Love controllers are smarter than what is needed for this application
but our choice was based largely on the fact that APS was going
to use these devices so support would be there; as well as spares in the
stock room.

Our choice of the GE Fanuc system is based largely on the programming
of the system.  The GE system looks as if the PLC program is easier to
maintain (although we don't plan to modify the program routinely).
We are planning to rely on support for the GE Fanuc 90-30 PLC by taking
advantage of APS-developed support for the 90-50 PLC that is being used 
or one part of the PSS.   The interconnect between the PLC and EPICS is:
GE Fanuc 90-30 -> RS-485 -> IP-485 -> MVME 162 (HiDEOS) -> 
                                      VME backplane -> MVME 167 (EPICS)
Notice that this is a one-way diagram.  In the APS design, EPICS is not
allowed to command the PLC; only make requests for information.

Seeing that many other CATs are planning to use Allen-Bradley PLCs, I wonder
if the ladder logic used in the AB PLCs is superior to the State Notation
Language available in the GE Fanuc 90-30.  Or are there plenty of 
Jedi knights out there?

Pete Jemian
  UNICAT