Re: [foxboro] OPC again...

We do extensive APC control via OPC.  This has been relatively
trouble-free.  A watchdog is a very good idea, and either automatic
fallback to regulatory control and/or a warning to the operator to
return to DCS control.

As Cory notes, DCOM can be avoided by having the OPC server on the same
box as the OPC client.  In many cases this does not mean that the APC
application has to live on the same box.

If you're using OPC for control, take a careful look at your underlying
platform.  Windows is getting fairly reliable, but cheap PCs are not.
Most of the OPC server reliability issues I've had to deal with have
been hardware related.  I'd look for a server class box with dual power
supplies and RAID.  If there is a big difference in $$ between the APC
application being on-line and off-line I'd lean towards redundant
servers and redundant data collectors.

I've used both Foxboro's OPC server and Matrikon's OPC server for I/A.
Matrikon's has been good.  Foxboro's is also good, although their OPC
HDA server had lots of growing pains.  Since I've had all 51 series
workstations, the OPC server has always been off-platform - this has
worked well.  Installing Foxboro's OPC server and AIM* on Win2K server
edition OS and Windows 2003 server OS have often had minor glitches, but
nothing that has kept the product from working.

Matrikon's OPC server costs more than Foxboro's but allows you unlimited
data collectors (running on different AWs).  Foxboro's OPC server
requires you to license additional data collectors after the first one
that comes with the product.

Regards,

Kevin FitzGerrell

-----Original Message-----
From: foxboro-bounce@xxxxxxxxxxxxx [mailto:foxboro-bounce@xxxxxxxxxxxxx]
On Behalf Of Corey R Clingo
Sent: Tuesday, May 01, 2007 3:58 AM
To: foxboro@xxxxxxxxxxxxx
Subject: Re: [foxboro] OPC again...

Personally, I would only use it in the manner Alex described: using a=20
watchdog in the CP with fallback logic and control.  Doing control with=20
anything that requires Windows and DCOM makes me nervous, but if it's=20
supervisory (like APC), you can at least implement a secondary
mechanism.=20

Most of the installation guides I've seen recommend opening things up
wide=20
to ease getting DCOM working properly, which of course is derimental to=20
security.  I have always taken that advice to heart, or avoided DCOM=20
entirely by putting client and server on the same box.


And I've always heard a persistent rumor that writing to the I/A via OPC

(not sure of the mechanism, maybe AIM*OPC?) was not a very high
bandwidth=20
proposition, but again, this may either not be true, or not an issue=20
depending on the size of the APC.


Corey Clingo
BASF Corporation






"Joseph M. Riccardi" <Joe@xxxxxxxxxxxxx>=20
Sent by: foxboro-bounce@xxxxxxxxxxxxx
04/30/2007 09:43 AM
Please respond to
foxboro@xxxxxxxxxxxxx


To
<foxboro@xxxxxxxxxxxxx>
cc

Subject
[foxboro] OPC again...






Folks,
I have always wondered if OPC was not just intended to collect data, or
is
it also considered a viable communication link for control?  I now have
a
vendor that wants to perform advanced process control from their
PC-based
software to specific control loops on the Foxboro System via OPC?  Read
measurement values, execute advanced control algorithms, write control
outputs, etc.
Is OPC considered secure, reliable, repeatable, etc. enough for control?

Your thoughts/recommendations?


Joseph M. Riccardi, Inc.
DCS Services - Industrial Process Control

North-Central Office (OH, PA, MI, IN, WV Area)
South-East Office (FL, GA, AL, SC, NC Area)

Joe@xxxxxxxxxxxxx

"To give real service you must add something that cannot be bought or
measured with money; and that is sincerity and integrity." - Donald A.=20
Adams




=20
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