Re: [foxboro] Operator interface question

What kind of thruput problems are you having?  Some of the issues I've had I
been able to clean up.

Brian Long
Green Bay Packaging
Arkansas Kraft Division

-----Original Message-----
From: foxboro-bounce@xxxxxxxxxxxxx
[mailto:foxboro-bounce@xxxxxxxxxxxxx]On Behalf Of Corey R Clingo
Sent: Wednesday, May 15, 2002 5:38 PM
To: foxboro@xxxxxxxxxxxxx
Subject: Re: [foxboro] Operator interface question




If the PLC logic is overwriting the value you are
incrementing/decrementing, then nothing will happen; the PLC ladder will do
this much faster than the I/A can.  But if the PLC logic is only reading
the value you are incrementing/decrementing, it should work as expected.

We have some gateway analog outputs like this, and the ramp keys do work,
but it can sometimes take a long time to see the results of your actions.
However, we do have throughput problems on our gateways, which I have not
been able to get to the bottom of yet.  If your gateway throughput is good,
it should work.

Corey Clingo
Sr. Engineer
BASF Corp.





stan <stanb@xxxxxxxx>@freelists.org on 05/14/2002 09:41:47 AM

Please respond to foxboro@xxxxxxxxxxxxx

Sent by:    foxboro-bounce@xxxxxxxxxxxxx

To:    foxboro
cc:
Subject:    Re: [foxboro] Operator interface question



On Tue, May 14, 2002 at 08:43:44AM -0500, Corey R Clingo wrote:
>
>
> One characteristic of most DCS PLC gateways is that the output values are
> silently read back behind the scenes so the operator is able to see
exactly
> what is in that PLC.  This causes confusion sometimes (i.e., when
operator
> actions have no effect because the PLC logic obliterated their change),
but
> is a reflection of the real world, and helps in situations like this.  I
> believe the Integrator 30 at least behaves in this manner.
>

I think I'm begning to gat a picture of how this should work.

However I still have a rather basic question. How can I read a value from
the PLC, and increment/decrement this value to write it back? If the AIN in
the gateway is in auto, I can't change the value in the DCS, right? If
instead, i make a copy, modify it, and write that back to the PLC, which
then detects the new data, and sends it back to the AIN, that I am
modifying, don't I have a timing race?

--
"They that would give up essential liberty for temporary safety deserve
neither liberty nor safety."
      -- Benjamin Franklin







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