This is an introduction to PLC logic . You can use PLC logic to build PLC programs with simple electrical circuit diagrams. In this article, I will use combinatorial logic to build the functionality of a PLC program. And to get as close as possible to real a PLC programming language like ladder logic, the PLC logic in this article will be contacts and relays in an electrical circuit . The first PLC program you will be building will be a very simple one. You will be using combinatorial logic to build your PLC program. The reason for this is that, a PLC program is really just logic . Everything in a PLC has two states, just like in digital logic. In logic the two states are called FALSE and TRUE. Sometimes these two states are referred to as “0” and “1”. Those two states are referred to as the numbers 0 and 1, so that we can use the them in binary numbers. Since the PLC works with two states only, it makes sens...