What is a PLC? PLC stands for Programmable Logic controller. PLC's are solid state device designed to to perform logic functions by internal relays which took the place of hardwiring actual relays together. If you ever have tried to wire circuits with relays and constantly change them to get the logic to perform as expected you understand why a PLC makes everyones life easier.

The Design of PLCs are similar to computers. The internal logic programmed in the forum of a Ladder which has all the logic is similar to a computer in which software programs utilize internal logic to run internal things where PLC's generally control external devices. PLC's can also be expanded easily giving you more options for relays, lower power usage, and virtually unlimited types of controls to perform PLC logic functions. PLC's have a combination of inputs and outputs that are wired to it from various devices.  Common inputs devices include proximity and roller switches. Common PLC output devices include solonoids, contactors, lights, relays and more.

What is PLC Logic? PLC Ladder Diagrams are basically ladder runs of PLC logic that stretches from one side of the screen to the other with coils on the other end. Ladder logic is very similar to how wiring diagrams are made if hardwired with only minor differences.