Once viewed as a transition tool in plant automation, the programmable logic controller maintains its relevancy by improving its functionality.
Suppliers of automation hardware have reconsidered the earlier assumptions. Unlike PC-based controls, PLCs are familiar, battle tested, reliable controls of plant floor devices. As their flexibility and functionality have increased, prices have declined.
"Everybody was promoting PC-based controls, but the dogs didn't eat the dog food because we basically tossed a PC control at plant engineers and said, ‘Have a nice day,'" suggests Mike Miclot, marketing manager for Rockwell Automation's ControlLogix line. "PC architecture posed problems in start-up phase. The operating system had to be integrated with existing systems, software had to be installed and harmonized, and everything had to be fine-tuned. Assuming you got through that, if something happens after it's deployed and operational-maybe IT wants to shut down the system to install a new Norton antivirus-then you have to reengineer it again."