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
