Re: [foxboro] Operator interface question
- From: "William C Ricker" <wcricker@xxxxxxxxxxxxxxx>
- To: <foxboro@xxxxxxxxxxxxx>
- Date: Tue, 14 May 2002 16:25:20 -0400
Some time ago we hooked up an AW70 or Micro IA station to
an A-B PLC 5 and wanted to do this same ramping thing. The
customer had an existing PLC-5 with some very old ops
intereface software. We were charged with making the ops
interface a Foxboro AW70/uIA setup, and to leave the PLC
alone.
What we wound up using was the AOUT block.
Now I don't have a system set up right now to test this out,
but my recollection is more or less as follows:
The AOUT block in AUTO always writes its output
value to the PLC every scan, so it more or less
owns the value in the PLC. Overwriting it from
PLC programming is only temporary, and the next
scan of the PLC block will set it to whatever the
IA block wants it to be. It this case, the IA
display must write the MEAS parameter of the AOUT
block to change the PLC.
The AOUT block when in MANUAL worked differently.
As I recollect, in the system as implimented, the
AOUT would read back the value from the PLC if it
(the AOUT) was in Manual. To effect a change in
the PLC, IA displays would write to the AOUT's
OUT parameter. In an increment/decrement, the
AOUT block would have the value read from the PLC
in the previous scan, modify it, and write it out
to the PLC.
The AW70 and uIA use a different block structure to get
data in and out of a PLC than that of the gateway, and
the AOUT operation may differ. The documentation doesnt
seem to say much about how this block actually runs in any
processor except the standard CP.
Also, there were some conciderations with block initialization
and such.
Answering the initial question, though, perhaps the AW70
and/or uIA is exactly what is needed.
(Maybe some enterprising soul with a gateway & PLC, or an
AW70 & PLC {and a bit of time} could give it a try.)
William C. Ricker
FeedForward, Inc.
Marietta, GA, USA
wcricker@xxxxxxxxxxxxxxx
770-426-4422
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