System Definitions

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Thread Starter

Richard George

Can anyone please tell me what the difference is between a Distributed Control System and a SCADA system in terms of basic architecture and connection of field instrumentation and equipment.
I have a client who is making me question my previous understanding (and sanity!)
 
SCADA… Supervisory Control And Data Acquisition, are systems usually connected to a PLC via serial link or ethernet.
 
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Kelvin Proctor

The definition I would give is that a distributed control system is one in where a number of 'smart' devices contain the control code and are distributed across a system. This is in comparison to a centralised control system where a single huge PLC might control everything with all I/O etc.. having to concerntrate back at the main PLC.

A SCADA system is a system that sits on top of the
control system, not performing machine level control etc..., that provides data logging and trending and addition operator interfaces to any custom interface that might have been builf for operators. A SCADA system usually just 'informs' a control system what thwe operator has requested, not undertaking control itself.

How this helps.

Cheers,

Kelvin
 
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Robert I Williams

The answer to your question can be somewhat convoluted in that PLC's also can do SCADA as can DCS. I have tried to explain the primary differences SCADA vs PLC vs DCS in the first edition of the Handbook of SCADA Systems. This book is now available for purchase as a CD by visiting www.scada-online.co.uk.

Since SCADA system RTU's can also come with a great deal of distributed functional logic then that system can also be a PLC or DCS system.

Primarily, the term SCADA has been related to remote data acquisition and supervisory control (i.e. setpoint modulation of a pressure or flow) and for remote control of end devices such as pumps on a long distance pipeline, either crude oil, gas, water, etc.

However, very recently I saw the term SCADA applied to interconnecting offshore platforms and onshore facilities where the primary SCADA function was information management and accounting.

Hopefully the text on the CD will be more clearer for you, if not, please let me know since the Second Edition is now being prepared and I am looking for contributions on the Table of Contents included on the website. First edtion TOC is also included.

Robert I

> Can anyone please tell me what the difference is between a Distributed Control System and a SCADA system in terms of basic architecture and connection of field instrumentation and equipment. I have a client who is making me question my previous understanding (and sanity!)
 
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