Re: [foxboro] Operator interface question

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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