Regarding Jeremy Pollard's column, "PLC Genesis" (June 2012), I have to weigh in with my (perhaps faulty) recollections of the programmable controller name transition from PC to PLC. In 1973 and '74, I worked for Texas Instruments (TI) designing anti-lock braking (ABS) controls. This, of course, is an automotive product, and the first programmable controllers were designed for the automotive industry, so TI's PC designers were in the same department. In 1974, they clearly were called PC for "programmable controller."
My next contact with programmable controllers was in 1979 at a publication printing company where a Modicon 384 was applied to control a rotogravure printing press. Programmable controllers were still called PCs at that time. The PC abbreviation also meant "printed circuit," but context usually sufficed to keep those two straight.
As we all realize, the IBM-PC brand name added confusion. Even Xerox tried using PC for "personal copier." One trade journal changed its name from PC Design to Printed Circuit Design, probably because people were disappointed to find that the magazine was not describing how to build personal computers.
I first saw "PLC" used by Allen-Bradley (I believe one of its models was called PLC-01) to distinguish its product from distributed control systems (DCS), which were primarily
concentrating on PID loops, i.e., analog control. The switch from PC to PLC seemed to happen naturally and quickly, with A-B not objecting to usurping its trade name and all of us users and instructors happy to be rid of the abbreviation confusion. Today it is PC (politically correct) to call them PLCs.
Marvin T. Anderl,
happily retired
