Transition from PLC / SCADA work to DCS...?

If one primarily does PLC and HMI programming (say Rockwell / AB products, GE Proficy), how much of a challenge would it be to transition into DCS work?

Essentially I am curious about the differences in design, programming approach, and implementation. Do you have to relearn a lot of things or is there enough commonality between the two (hardware and software) that there isn't a huge learning curve?

From my experience, SCADA and DCS different and they are not interchangeable. SCADA is at the lower level compare to DCS. With Rockwell software and hardware you can only achieve the SCADA level because the data transmission time between the Allen-Bradley PLC and the Rockwell HMI cannot achieve the DCS requirement. For DCS the hardware and the software are cooperating so well that the data transmission time between them both is minimum.

I think working on DCS product such as Honeywell or Yokogawa DCS is easier than SCADA because in DCS almost everything are standardized with typical library with very less customization. However in SCADA this is not the cast as we need to build our own library.

I think the most challenging part is switch from SCADA to DCS. Once you are used to DCS already you will find that for very big system such as an entire plant or offshore platform DCS is more convenient.

If you're used to doing (only) ladder logic in PLCs, then DCS is a whole different world with a whole different mindset. But if you've used some of the Higher-end tools such as Siemens' "CFC" add-on to Step7, then it's not that much different. In fact, Siemens' DCS system (PCS7) is just Step7+CFC+SFC+SCL+ a few other add-ons.

Allentcm is right, DCS is much more library-oriented than PLC/Scada. You either use ready-made libraries from the DCS vendor or create your own. You create a function block to describe the typical control loops that you have, store it in a library, then build your system using hundreds or even thousands of instances of the library objects.