DCS vs PLC

Good day. is there any distinct difference between these two powerful controllers regarding the transformation off the PLC over the years?

If you search the site you will find a lot of threads on this topic.

The differences are blurred nowadays, and many DCS will tie into PLC networks. In general PLCs are, in my opinion, easier to program less expensive. If you look at the PLC subset called PAC (Programmable Automation Controllers) the differences are even less.

DCS Systems were created for large, plant-wide process control. Back in the early days, PLCs couldn't generally handle this, either because analog control wasn't as available or because the sheer number of I/O points would make DCS more economical than a PLC. To put it simply, a PLC controls a machine, a DCS controls an entire facility.

But as Tom said above, the increase capability of PLCs has blurred the lines a lot, and especially in the case of PACs (Programmable Automation Controllers) like the Control Logix from Allen-Bradley or the Quantum from Modicon, which will pretty much do almost everything a DCS will.

Bottom line is, how tightly integrated do you want your system and how much I/O do you have? I'd only recommend a DCS if you have something like 5,000+ I/O points spread out through an entire plant and you need to coordinate them all.

PAC is a bull***t term - invented to increase sales. I know, I did work for the company that originated it! They are just PLCs with extended capabilities - many PLC manufacturers do not use the term and have products that will kill most of the so called PAC controllers!
Generally, from my experiences, DCS are quite good at handling lots of I/O but the communications are so slow when the I/O numbers go up it is not funny.
I prefer to use distributed PLCs with good comms networks.
For remote I/O I will not use Ethernet IP either - lots of stuff on the network usually anyway and there are some really good remote I/O networks out there.
My favourite is CompoNet - unfortunately only Omron seem to have taken it on - 1000 I/O updated in 1 ms over 30 metres - awesome! Profibus and Device Net are really slow compared to that.
Then Ethernet IP between PLCs.
Even Ethernet IP struggles - I have one job where there are 17 PLCs with lots of stuff being transmitted from all PLCs to all PLCs. When I connect with my programming software and monitor/online program 10 PLCs the network crawls to a snails pace - almost as slow as serial! There are 14 more PLCs to go on the network - I am thinking of putting in another network as it will get really slow - 1-200 ms network transfer time is not good enough! LOL
In future on heavy network jobs I will use EtherCAT if I can - it is far more efficient - maybe even use it for remote I/O as the network use will be way down. EtherCAT has really tight and fast network packets and a wire ring comms can be implemented with detection of cable break between nodes. Check out http://www.ethercat.org/default.htm