PLC origins: Where did PLCs come from? 40th anniversary timeline

PLCs have undergone 40 years of convergent evolution, according to an article in the upcoming September issue of Control Engineering. See a graphic with a timeline of PLC development, a market that went from zero to more than $1 billion in a decade. Link to the full story.


Programmable logic controllers (PLCs) were more of a technology evolution than a startling discovery according to Control Engineering in the upcoming September North American issue. [See link below.] “The earliest robust, easily re-programmed industrial controller—which we know as the PLC—evolved nearly concurrently along three independent paths.”


Three tributaries converged to form today


Ball’s research for the


40th anniversary PLC article in Control Engineering

showed that PLC evolution involved five companies: Bedford Associates; General Motors Hydra-matic Division, Ypsilanti, MI plant; International Instruments Inc. (3I); Digital Equipment Corporation (DEC); and Struthers-Dunn Systems Division in Bettendorf, IA. He says that identifying the needs and early ideas first began to take shape in 1967. Documentation and actual building of prototype devices started in 1968, with early model deliveries and factory tests taking place in 1969 and ’70.
“Probably the most publicized early PLC development took place at GM’s Hydra-matic Division plant,” he says. “Several engineers there collaborated on a concept for what they called a‘standard machine controller.’ ” 
The GM engineers envisioned a controller to replace troublesome relay panels and provide a simpler interface between computers and machines.
Meanwhile, a second path was being pursued by Bedford Associates, a small New England company that today would be categorized as a control systems integrator. Bedford Engineers developed a controller to replace costly minicomputers and reduce programming time for various machine tool applications.
The third approach underway at the time occurred at the Struthers-Dunn Systems Division, which also had strong automotive ties and was well aware of relay and timer panel shortcomings.
Early on, the controller was known as the PC and publications such as the PC Insider popularized the designation. This was fine until personal computers arrived around 1980 and this office/consumer item stole the PC acronym. To avoid confusion, controls people reverted to a PLC designation — a term that had been registered by Allen-Bradley for their newer model controllers.“ Allen-Bradley has been quite gracious,” Ball says, “and has not attempted to restrict the use of the term.”
Shortly after the PLC debut, sales went from zero to more than a $1 billion in a little more than a decade.
C.G. Masi, senior editor
Control Engineering News Desk
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