Most PLC allow more than one output for each row (Rung).
The Processor (or "Controller") explores rungs of the ladder from top to bottom and from left to right.
The input instructions are the conditions that the circuit has to let or not let to pass current from one line to another. These conditions
are commonly handled with normally-open or normall-closed contacts which interpret the high and low signals of sensors or switches. If
conditions are true the current reaches the output instructions, which generate actions such as energizing a motor coil or power on a
lamp. In this way the flow of current to the output coils is conditioned by the logic managed by the input instructions.
A PLC has many input and output terminals, through which "high" or "low signals are produced " to be transmitted to power lights,
solenoids, contactors, small motors and other devices provided to on / off control. In an effort to make PLCs easy to program, ladder
programming language was designed to resemble ladder logic diagrams. Therefore, an industrial electrician or electrical engineer
accustomed to read ladder logic diagrams will be more comfortable programming a PLC if the ladder language is handled.
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