Also known as Programmable Logic Controllers, PLC processors are dedicated computers used to manage industrial processes. While they come in all shapes and sizes, you can think of the larger ones as being much like servers only they manage physical processes rather than purely informational ones. Other processors may be small enough to fit in your pocket, but they all work in the same fashion.
PLC Processors vs. Computers
Like a general purpose computer, a PLC system has a number of different components. Each one has a CPU, a power supply, working memory and communications interfaces. The biggest difference is that where most general purpose computers handle a wide range of functions, the majority of control systems and PLCs perform a single dedicated function.
While any given PLC installation is usually only going to control a single process, it still requires programming because the same processor type usually works with a wide range of different applications. PLC software is designed to let you tune your PLC processor to meet your specific needs in much the same way conventional software does in your computer. The primary difference is that a PLC only runs one piece of software at a time.
Most industrial automation systems rely on PLC controls to do their work. That means that PLCs rely on designs that help them handle the conditions you find on a factory floor rather than in a stable climate-controlled server room. These units are ruggedised and protected against everything from temperature extremes to particulate matter.
The big advantage of a PLC based system over hardwired relays and other controllers is its flexibility. Because it can go through reprogramming, a PLC can adjust to do different jobs as the situation changes. You can add new sensors and outputs to the same machine and then program your existing controller to take advantage of it. It makes system upgrades much easier than ever before.