The following example of a baseline ladder logic program for a silo plant illustrates the graphical programming language for creating software for programmable logic controllers (PLCs). It is one of the languages specified by the IEC 61131 standard for use with PLCs. In the following example, a program is a circuit diagram that emulates relay logic hardware circuits. The term ladder diagram refers to the program's resemblance to a ladder with two vertical rails and horizontal rungs. In the ladder diagram, the rails are referred to as "power rails." When implying the ladder logic program in a PLC, it is critical to understand the seven basic parts of a ladder diagram.
