difference between DCS and PLC

[rob63]

I was just wondering why a setup would be referred to as a DCS rather than just a standard PLC system?

I was on a site the other day and it was the first time i had come across this particular phrase. The setup was a couple of 300/400 controllers in a switch room with an engineering station essentially a pc running pcs7. This was connected to a few remote i/o next to the machine.

The only difference i can see (i don't know very much though :-\ ) from a standard setup controller setup was all of the i/o was able to view on a pc rather than plugging a laptop in??

 

[RET]

Here's a good read.

https://w3.siemens.com/mcms/process...iles/pcs7/support/marktstudien/PLC_or_DCS.pdf

 

[mk42]

See a similar thread, and my post from it below:

http://www.plctalk.net/qanda/showthread.php?p=660813

Simatic Manager/S7 is a PLC programming package, which could be combined with a SCADA or HMI package to allow for control. You can program whatever you want, but it doesn't do much to get you pointed in the right direction.

PCS7 is a DCS (distributed control system), which includes HMI, PLC, IO, ETC. These tools are typically used in Process facilities, like chemical plants, oil refineries, etc.

PCS7 combines S7 v5.5 and WinCC SCADA, and adds a bunch of extra stuff to integrate them. It makes the code very structured, based on the idea of a Process Object, which is one motor, one valve, etc. The PO includes all the values for that objects, including setpoints, actual values, temperature, runtime, maintenance data, etc. It includes libraries with both code for common types of objects, as well as HMI faceplates that automatically link to them. It allows you to organize these process objects by the area of the plant they are in, so you can easily monitor how your plant is performing.

The difference between PLC + SCADA and DCS is more historical then practical. Now, both types of systems can do most of the same things, but 20-30 years ago the differences were much bigger. The difference now is mostly on the approach to programming, and how the customer wants to think about his solution.

 

[rob63]

Excellent explanation MK42. I read a few (old) threads about it elsewhere and it just confused me. The idea behind it is pretty obvious to me now.

 

[rob63]

Thanks for the link RET. I'll have a good read through.