TABLE OF CONTENTS In this chapter we will review Ladder Diagram, the second graphical language of the IEC languages in the set:
Structured Text, Function Block Diagram, Ladder Diagram, Instruction List and Sequential Function Chart.
Ladder Diagram can be used to express the behaviour of functions, function blocks and programs, and also actions and transitions in Sequential Function Charts.
In this chapter we will review:
The graphical symbols and conventions used to describe Ladder Diagrams;
How Ladder Diagram is based on a concept of power flow between contacts which can control the operation of notional coils that represent variables;
How to develop complex boolean logic expressions;
How to control functions and function blocks through using connections on a Ladder Diagram rung ;
How to control ladder rung execution using jumps and labels ;
Restrictions on the portability of code between ST, FBD and LD.
Ladder Diagram has been developed by the IEC by considering the most commonly used symbols and terminology used in mainstream PLCs. To anyone who is already familiar with writing programs using relay ladder , the symbols defined in IEC 1131-3 will not bring any unwelcome surprises.
If you are not familiar with this form of graphical programming, it is recommended that you read the introduction given in Chapter 1 where some of the main features and limitations of the language are discussed.
Ladder Diagram is based on a technique used to design logic using relays. A Ladder Diagram always has a left hand vertical power rail that...
