PLCs monitor, control, and communicate with your automated processes

Prior to the PLC, a control system for a machine consisted of individual components such as relays, timers, and counters. The PLC replaces all of those. Imagine a system with hundreds and hundreds or even thousands of individual relays timers and counters and all the wiring that it took to connect all of those pieces. Every time that someone wanted to change the function of the machine in any way, you would have to rewire it to achieve the new function. If there was a problem that needed to be diagnosed, a technician would have to start checking the individual components and connections and remember that there may be thousands of them. A PLC works by monitoring the state of inputs, executing the code or logic, and turning on outputs based on the combination of the inputs and the logic. This allows the PLC to replace all of those relays, timers, and counters with a single box that can be reprogrammed to handle a new task instead of rewiring. Even the footprint of the control systems was dramatically decreased.

Once the Personal Computer was introduced (the PC we all think of) engineers had a new easier way to program their controllers and the term was changed from Programmable Controller to Programmable Logic Controller. Now, nearly 50 years after the first PLC, the PLC is running the majority of automated machinery around the world.