With the venerable programmable logic controller (PLC) marking its 40th anniversary last year, I got to thinking about its timeline. It goes way back in my engineering career — the career before my involvement with Control Engineering magazine. So I asked a fellow engineer, whose involvement in the control industry includes more history than mine, what he thought.
"There's evolution and then there's revolution," said Bill Southard, president and CEO of DST Controls, a systems integrator from Benicia, CA. "Mr. (Dick) Morley sparked a revolution in machine building techniques with his introduction of the PLC (actually then called a 'programmable controller' or 'PC') back around the time the earth cooled. This created excitement and benefited the machine builder in three very major ways," he says.
The first and foremost benefit was the reduction of time it took to design, prototype and then build a machine. This benefit was derived from the fact that the logic could actually be worked out while the machine and control panel were being built, not after all the relay logic diagrams were completed and checked.
Secondly, machine builders could easily reprogram the PLC to add new features to both new and existing machines, thus extending the life of the products.
Lastly, the control panels associated with the machinery could be smaller, making it possible to mount the controls on the machines rather than on an entire wall.
"All of the above resulted in significantly lower costs to the machine builders in both manpower and hardware," Southard says. The programmable automation controller or PAC (essentially a ruggedized PC in a PLC-like form factor) is "merely an evolutionary product that extends the mighty power of the good old PLC," adds Southard. "Now, it is specifically designed for connectivity and distributed I/O, thus continuing to make design easier. But, alas, so do the new terminal block designs. Read the rest of this article from Control Engineering and browse through a list of most-purchased-from PLC and PAC manufacturers: Programmable Logic Controllers, Automation Controllers
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