Ladder Diagram (LD)¶
The Ladder Diagram is also a graphics oriented programming language which approaches the structure of an electric circuit.
On the one hand, the Ladder Diagram is suitable for constructing logical switches, on the other hand one can also create networks as in FBD. Therefore the LD is very useful for controlling the call of other POUs.
The Ladder Diagram consists of a series of networks. A network is limited on the left and right sides by a left and right vertical current line. In the middle is a circuit diagram made up of contacts, coils, and connecting lines.
Each network consists on the left side of a series of contacts which pass on from left to right the condition “ON” or “OFF” which correspond to the Boolean values TRUE and FALSE. To each contact belongs a Boolean variable. If this variable is TRUE, then the condition is passed from left to right along the connecting line. Otherwise the right connection receives the value OFF.
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