Feedback: Criteria for PLC vs. DCS evaluation


I read your article about the Eli Lilly engineer’s (Mike Alward) comparison of PLC versus DCS. [ Control Engineering Weekly News email newsletter, Oct. 31, 2006; “ Automation Fair: Pharma engineer rates PLC system over DCS .”]

What were the 19 criteria used to compare? This is so I can understand the viewpoint of giving a 77-73 lead to the PLC. We do run into the comparison once in awhile, and, yes, it [the DCS advantage] does seem to disappear, as PLC functionality gets closer to the DCS. Thank you.
—James Pfeifer, R.E.T., F.S.E, senior control systems specialist, IMV Projects , Calgary, Alberta, Canada

PLC vs. DCS criteria are…
I appreciate your feedback on the PLC versus DCS debate. For those just picking up the discussion, the article, linked above, compares a control system based on programmable logic controllers and distributed control systems. While I included some criteria provided by Mike Alward, lead system architect at Eli Lilly (Indianapolis, IN), I should have figured readers would want them all.

Here are the 19 criteria Alward mentioned:

  1. Control execution speed

  2. Control templates provided

  3. Control templates, ability to create

  4. Control, advanced

  5. Control, analog

  6. Control, machine

  7. Cost for implemented system

  8. Global tag, parameter accessibility

  9. HMI development / integration

  10. Integrated hardware solution

  11. Integrated software solution

  12. Integration of non-vendor provided components and applications

  13. OEM equipment, ease of integration with

  14. Programming language capabilities

  15. Recipe functionality

  16. Redundancy, fault tolerance

  17. Scalability

  18. Security, logical

  19. System integrators, availability of effective

For more Control Engineering research and trends on PLCs and on process control, read:

Also, type the words control systems in the search box atop any page at for other related reading.

—Mark T. Hoske , Control Engineering editor in chief

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