When to PLC's and SCADA become DCS?

ihc · Dec 28, 2004

Hello,
Hopefully this is relatively simple to someone with DCS experience, what defines a DCS system? I have seen many SCADA and PLC projects selling themselves as DCS but i confess to not knowing the definition. Unfortunately a google on the net didn't produce a definition. Thanks.

Allen Nelson · Dec 28, 2004

There is no base I/O count, no feature, no number that defines "DCS" and "PLC/SCADA" in anything that an engineer would understand.

These are marketing terms, not engineering ones. A system is a DCS when someone sells it as a DCS.

Tom Jenkins · Dec 28, 2004

A "classic" DCS consists of conventional PID controllers linked with a communications network with a computer graphic interface for status and tuning. A "classic" SCADA consists of RTUs (remote terminal units) connected by a serial or radio telemetry link to a computer interface. As Allen points out the lines between DCS and SCADA is blurred, and nowdays PLC, PID controllers, and RTUs can exist on a single system.

akreel · Dec 28, 2004

If they and try to sell you the chairs with your operator consoles, it's probably a DCS.

The day I realized the difference between a PLC and a DCS, was the day I found a specification and part number in a Bailey manual for a gray office chair!

AK

ihc · Dec 29, 2004

Thanks for the replies, i now understand why i didn't understand.

Ken Moore · Dec 29, 2004

akreel,
We have a Foxboro DCS, and they sell the chair AND operator station.
We have one, looks like something from the 1960's STARTREK TV series.
Has 6 monitors run by two Sparc stations and four x-terminals.
It was bought with the original installation and cost an arm, two legs, and a torso.

Now that's a DCS.

Ken

leitmotif · Dec 29, 2004

OK I'll plead ignorant.

What do acronyms SCADA and DCS stand for??

Dan

Ken Moore · Dec 29, 2004

DCS= distributed control system
SCADA= supervisory control and data acquisition

Ron Beaufort · Dec 29, 2004

Greetings ihc,

I doubt that you’ll need anything beyond what has already been posted ... but this post seems to have helped a few people get a “big picture” idea of what’s involved ... just be sure to notice the “disclaimer” near the top ... as everyone else has said, basically there are no “hard and fast” rules when it comes to defining the differences between one type of system and the other ...

and welcome to the forum ...

When to PLC's and SCADA become DCS?

ihc

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Allen Nelson

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Tom Jenkins

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akreel

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ihc

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Ken Moore

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leitmotif

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Ken Moore

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Ron Beaufort

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