Feedback: Criteria for PLC vs. DCS evaluation

By Control Engineering Staff November 17, 2006

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:

Control execution speed

Control templates provided

Control templates, ability to create

Control, advanced

Control, analog

Control, machine

Cost for implemented system

Global tag, parameter accessibility

HMI development / integration

Integrated hardware solution

Integrated software solution

Integration of non-vendor provided components and applications

OEM equipment, ease of integration with

Programming language capabilities

Recipe functionality

Redundancy, fault tolerance

Scalability

Security, logical

System integrators, availability of effective

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

“Process Automation Trends”

“PLCs Maximize Machine, Motion Control”

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

—Mark T. Hoske , Control Engineering editor in chief