Hello,
I am preparing a presentation about DCS´s in my workplace, and I don´t seem to explain clearly what “distributed” stands for in the term DCS.
I have some Ideas:

* The field devices are distributed
* The operator and development stations may be distributed
* The algorithms are distributed
* Many DCS´s in different processes of the plant (distributed as well!)

Do you have other ideas? Or can someone tell me what Distributed meant originally?

Thanks for your help!

 

The term "Distributed" as used in DCS was coined by Honeywell in 1976 when they introduced TDC-2000 (Total Distributed Control).
What they meant was that the control computations were distributed to many microprocessors, one per controller. The controllers were
originally intended to be distributed about the plant to save money on wiring, but quickly that was found to be too difficult to
maintain. Geographic distribution was also expensive since the controllers were not environmentally rugged and needed to be in a
protected area such as the control room. The DCS used many of the ideas developed for Direct Digital Control (DDC) that were
originally implemented on centralized mainframe and minicomputers. Therefore, distributed was contrasted to centralized - a good
reference.

The real contribution to the science of control was the TDC 2000 dual-redundant data highway - a slow but highly reliable network
allowing the exchange of data and status among the "distributed" controllers. TDC 2000 popularized the concept of the video-based
operator station, although that feature had been previously available on earlier computer-based control systems.

Dick Caro
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DISTRIBUTED IS NOTHING BUT DISTRIBUTION OF CONTROL SIGNAL AT VARIOUS LEVELS (VARIOUS CONTROLLERS LOCATED AT DIFFERENT PLACES IN THE PLANT AND ALSO CONTROL ACTIIONS PERFORMED BY THE I/O CARDS ITSELF)

 

Dear Alvaro,
The term is quite ambigous to convey a definite meaning. In 1997 during the design of a 1500 TPD Fertilzer Plant in Saudi Arabia, we have applied the concept in a generic "Distributed" fashion.

We were putting up a new plant adjoing an existing one while two more similar plants were planned for future. There we had adopted the concept of a centralised Control Room with satellite rooms (SRs) acting as Process Interfaces. All DCS control hardware was placed in the SRs. The SRs were in the vicinity of the process plants but out of the classified limits. The inter-connectivitity achieved with fiber optics.
The concept has worked fine, but whether it fits the term is another matter.

Sajid