In the beginning there was the relay and the timer. And in the process industries, there was the
hardwired controller. A generation ago, digital electronics made the hardwired relay and controller
obsolete in favor of the PLC, the programmable logic controller. Made to be fully deterministic and
have limited control functions, PLCs were able to sweep hardwiring into the dustbin because they
were easy to program in the "ladder" style of electrical wiring diagrams, and they were easily re-
programmable so that they could accommodate changes on assembly lines and in batch
processes.But PLCs are limited. Ladder-logic programming cannot be used for complex mathematical
formula, such as the basic PID algorithm found in every single loop controller in a process plant,
for example. Then, along came the PC. Inexpensive computing power became ubiquitous and
easily affordable. PCs were tried early on in industrial control, but early operating systems and hardware were not up to the stresses and standards of the industrial workplace.
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