Re: [foxboro] Off platform communications

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
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        your own risks. Read
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_______________________________________________________________________
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