PLC & DCS 1

[mohdalharbi]

In control system of small plants (power or water ....etc)
we will use PLC to control and monitoring Data, while in big plants we will use DCS so the control will be direct through the DCS in the main control room.
I read that we can divide plant to many parts each control and monitoring with one PLC in the site, the sum of PLCs will connect to the control room it may call DCS. what is the differece between PLC and DCS and can we connect many PLCs together in control room how and through what can we say master PLC and sleeve PLCs and can we call master and sleeve PLCs a DCS system or DCS is another type of techniq.

 

[jsummerfield]

Traditionally, a few aspects differentiate the PLC and DCS product lines. The PLC developed along discrete logic as relay, timer and counter replacement with sequential control capability. The DCS was developed to replace the analog regulatory control. The PLC was sold as hardware in a box. The DCS was assembled, tested and shipped as a system. The DCS supplier was more likely to offer the configuration programming services as an option. The DCS was historically a closed system and PLC a more open system.

There could be several issues to address. It would be best if the remote PLCs are identical or have similar communication features. This is unlikely if the PLCs were furnished by assorted equipment manufacturers.

A central PLC (such as an Allen-Bradley PLC5) can communicate with remote PLCs even if they a somewhat different (such as A/B SLC-500). Wonderware, Intelutions, GE, Rockwell and others offer PC based operator workstations. Also, some DCS manufacturers offer a "hybrid" system that interfaces remote PLCs to a DCS operator interface. If this is a green site with mostly regulatory or batch control, I would also consider remote DCS controllers or remote DCS I/O in addition to interfacing the PLCs.



John

 

[ilan7]

mohdalharbi
The company I work for, we started with small turbines of 300KW and as the years goes by, the units grow, and we are building power plant of over 100 MW each.
We always worked with PLC's and HMI programs to control the plats as the price was about 10% of the price of the same size DCS system. Nowadays the DCS price went down, but still it is cost more then double to use DCS.
The big advantage of the DCS is for the Chimical and Petro-Chimical plant when all the controllers you need as well as spacial programs for controlling and simulating reactions are build in. For us at the Power generation plant, there are no benefits which the PLC (or few PLC's Connected) + HMI program can not handle. See some of our plant at:

http://www.ormat.com

 

[sai1780]

I am working as training officer. I want the the basics of DCS systems for my students. Please mention some useful sites.
Thanks