Re: [foxboro] Off platform communications
- From: "Johnson, Alex (Foxboro)" <ajohnson@xxxxxxxxxxx>
- To: foxboro@xxxxxxxxxxxxx
- Date: Fri, 24 May 2002 18:39:44 -0400
I will take this opportunity to point out a significant issue with using OPC
Servers on the I/A Series.
Most current OPC Servers use one-shot sets to write values to the process
CBPs from a remote OPC Client. This works pretty well as long as the volume
of data is similar to that of an operator's console. There is noise that our
OPC Server will offer connected writes as a high speed alternative. However,
as readers of this list know, connected writes have issues too.
To refresh our memories:
1) One-shot sets in the worst case:
a) generate broadcast traffic,
b) are slow since they require the remote station to reply, and
c) carry only one value per message.
2) One-shot sets in the best case, the broadcast is eliminated often at the
expense of the IMPORT table which
by default is quite small. When it fills broadcasts are back in use.
3) Write lists secure the target C:B.P and the point remains secured if the
OPC Server or its station die. This
makes backup OPC Servers with write lists problematic. You can do backups
with one-shots without issue.
Now, consider Troy's note. He wrote that an older application had
"successfully used the Data Poke utility to input data from spreadsheets
back to DCS" and that it did "not need to pull large amounts of data back
into the DCS."
However, he went on to add that he is " looking for is a real-time interface
to display" process data for his operators."
When I read those words, a red flag went up.
If the data volume in such an application gets too high (10/20 points per
second would do it), you will have a inordinate amount of traffic if the
data is stored in a CBP and one-shot sets are used.
This amount of data flow seems likely when I read the words "we are looking
for is a real-time interface to display a limited amount of SCADA data to
our operators." Experience tells me that the need is higher than the system
will tolerate or will be soon after installation.
So, the options are:
1) Use an OPC Server and store the data in CBPs with the network traffic
that might entail.
2) Use an OPC Server and store the data in Shared Variables (no network
traffic and the one-shot sets are faster)
3) Use an OPC Client on the I/A Series side and avoid the issue altogether.
Any of these options will work, but you need to understand the tradeoffs.
In the first case, you could over burden your target CP and if broadcasts
occur your CBLAN and otherwise uninvolved stations on the network.
In the second case, you will need to create the shared variables at bootup.
a) Using the omcrt tool, this requires 12 seconds per SV. This is very
slow.
b) Using the ommcrt tool, you can create 20 variables of the same type in
one 12 second interval.
This is 20 times as fast, but still slow.
c) You will need to use the ICC to connect the SVs to blocks in the CP if
you want them alarmed or to have
detail displays
The third case eliminates all of these issues and lets you build blocks to
hold the data.
There is actually a fourth possibility using application objects, but that's
a story for another day.
Regards,
Alex Johnson
Invensys
10707 Haddington
Houston, TX 77063
713.722.2859 (office)
713.722.2700 (switchboard)
713.932.0222 (fax)
ajohnson@xxxxxxxxxxx <mailto:ajohnson@xxxxxxxxxxx>
Come to the Invensys Showcase: http://www.invensysshowcase.com/
<http://www.invensysshowcase.com/>
-----Original Message-----
From: Mark V. Urda [SMTP:mvurda@xxxxxxx]
Sent: Friday, May 24, 2002 12:38 PM
To: foxboro@xxxxxxxxxxxxx
Subject: Re: [foxboro] Off platform communications
Troy-
Assuming that your IA system has at least one AW51 (4.3 or higher)
or AW70
(6.1 or higher) with a second ethernet port, then I suggest that you
use the
AIM * OPC Server. AIM * OPC Server software can be installed on
directly on
an NT/2000 based PC or directly on Intellution SCADA node, if it is
NT/2000
and has adequate resources. IA OPC Server can be accessed by
Intellution OPC
client for read and write access to IA database.
>From the Intellution OPC Driver Help File, is the following
description of
Intellution OPC I/O Driver:
The OPC I/O driver is an Intellution version 7.1x I/O driver that
provides
the interface and communications protocol between OLE for Process
Control
servers and your process control software. Intellution version 7.1x
drivers
are designed with the following attributes to provide flexibility
and
ease-of-use:
OLE Automation technology.
FIX integration.
Event-driven architecture.
OLE for Process Control compliance.
OLE Automation Technology
Version 7.1x drivers incorporate OLE Automation technology and can
therefore
expose their features to scripting tools and other applications.
Because
the drivers are OLE Automation applications, you can:
Create and manipulate objects exposed in the I/O Server from another
application.
Create tools that access and manipulate driver objects. These tools
can
include embedded macro languages or external programming tools.
The I/O driver consists of the following OLE components:
The I/O Server The core executable program. The I/O Server
maintains the
OPC server, group, and item objects, performs all required functions
for
communicating with third-party OPC servers, and exposes the methods
and
properties to other applications.
The I/O Driver Power Tool A client application to the I/O Server
with a
graphical user interface. The Power Tool accesses the I/O Server
and lets
you view and modify OPC server, group, and item properties.
You can also view and modify driver properties with a custom client
application developed specifically for your system. Refer to
Creating
Custom Client Applications to learn more about creating your own
client
application.
Integration with the FIX
Intellution version 7.1x drivers let you automatically add addresses
to the
driver configuration while you are configuring your FIX database.
When you
add a block to the database that accesses a point in the OPC server
that you
have not configured, the point is automatically added to the I/O
Server and
polled for data. Refer to Feature: Creating Items Automatically in
FIX
Database Builder.
Event-Driven Architecture
Version 7.1x drivers are event-based rather than time-based,
reducing CPU
time and increasing performance.
OPC Compliance
The OPC Client driver complies with the OLE for Process Control
(OPC) v1.0a
standard. The OPC Client provides the ability to bring data from
any OPC
v1.0a server to Intellution's FIX Human-Machine Interface (HMI)
software.
The OPC Client driver is also compliant with the v2.0 standard.
1997-99, Intellution, Inc. All Rights Reserved.
We have been using AIM* OPC Server for the last six months to
develop
solutions interfacing IA to OPC aware applications like Fix,
WonderWAre and
other third party HMI and other applications.
The Foxboro part number for Real Time Data Access is Q0301UT, and is
described as:
FUNCTION: The AIM*AT OPC DA Server Is An OPC V2.04 Compliant Server
That
Provides OPC Client Software With Access To I/A Series Object Data
And To
Real Time Point (RTP) Data In The AIM*Historian. The DA Server
Software
Provides Read And Write Access To Object Data (C:B.P) In I/A Series
Via Both
The AW51 (Solaris) And AW70 (Windows NT) Platforms. The AIM*OPC
Server
Resides On A Windows NT Or A Windows 2000 Platform.
PSS can be accessed via
http://www.foxboro.com/iaseries/pss/21s6/21s6d10b4.pdf for more
info.
This should provide the most cost-effective solution since no new IA
stations are required, and software runs on PC platforms.
Best regards,
Mark V. Urda
Synergy Systems Inc.
528 West 5th Avenue
Naperville, IL 60563
phone: 630-778-1960
fax: 630-778-7926
cell: 630-248-9382
-----Original Message-----
From: foxboro-bounce@xxxxxxxxxxxxx
[mailto:foxboro-bounce@xxxxxxxxxxxxx]On Behalf Of Troy L Brazell
Sent: Friday, May 24, 2002 9:03 AM
To: foxboro@xxxxxxxxxxxxx
Subject: [foxboro] Off platform communications
We need to connect or I/A system to Intellution via the company WAN.
We do
not need to pull large amounts of data back into DCS. We us DataLink
and
Data for Windows on older systems to get information out of DCS and
into
Intellution. We has successfully used the Data Poke utility to input
data
from spreadsheets back to DCS, however, what we are looking for is a
real-time interface to display a limited amount of SCADA data to our
operators. Anyone have any ideas?
Thanks
Troy
**************************************************
A lack of planing and communication on your
part does not constitute an emergency on my part!
Troy L.Brazell
Duke Energy Field Services
Automation CCST
Mid Continent
Borger, Texas
tlbrazell@xxxxxxxxxxxxxxx
Cell 806-898-4340
Office 806-275-5274
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Process
Systems (formerly The Foxboro Company). Use the info you obtain here
at
your own risks. Read
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_______________________________________________________________________
This mailing list is neither sponsored nor endorsed by Invensys Process
Systems (formerly The Foxboro Company). Use the info you obtain here at
your own risks. Read http://www.thecassandraproject.org/disclaimer.html
foxboro mailing list: //www.freelists.org/list/foxboro
to subscribe: mailto:foxboro-request@xxxxxxxxxxxxx?subject=join
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