Is there any difference in hardware of PLC and DCS system?

 

Basically there are lots of differences. Let me start with the explanation of application of a PLC and a DCS.

1. PLC as understood from the name (Programmable Logic Controller) executes some logic operations (like AND,OR,NAND....) on the inputs and gives you a logic output (0 or 1). This is the basic definition of a PLC, but today almost all PLCs can perform analogue operations on the inputs and can handle also analogue outputs. A PLC starts executing lines of a program one by one up to the end of the program and then starts to execute the same program again and again...

So with this explanation you expect to have one central porccessor for a PLC. If you use one PLC for a large plant (let's say a refinery) and this PLC fails, all the plant will stop.

2. DCS systems, on the contrary, are not used for logic operations. They have some multi-function controllers. Each multi-function controller has some controllers in itself and can control, for example, 8 instrumentation loops. These controllers, like a physical controller, can perform PID functions. Each multi-function controller has its own proccessor. So in a large plant they divide the functions in different groups, and each group of functions is assigned to one multi-function controller. So if the proccessor of one multi-function controller fails, other groups will continue their operations and the plant will not stop completely. That is why they are called DCS (Distributed Control System). It means the control responsibilities are distributed.

In DCS systems there is also one PC which functions as an HMI system to change and control the partameters of the controllers. Connection between this PC and the multi-function controllers are notmally done by an industrial network.
Comparison between a PLC and a DCS system is like comparing an orange with a watermelon.
They are both elecronic parts of a control system but with different specifications.
In PLC case we have Analogue input/output modules. In DCS we don't have them. In PLC case we have memory boards in DCS we don't have them.
This is enough for now.
If you think I can help you please feel free to contact me at

ubtrefkou_5432 @ yahoo. com

You are most welcome.

 

Thanks for replying.

Suppose you have a PLC system of ABB connected in Ethernet TCP/IP. Can you connect a ABB DCS controller in the same network?