Ladder Logic Fundamentals and Programming Examples - PLC Tutorial
Logical continuity vs. electrical continuity
Mastering examine onon and examine off instructions
The PLC scanning process
PLC Programming Languages
- In the United States, ladder logic is the most popular
method used to program a PLC
- This course will focus primarily on ladder logic programming
- Other programming methods include:
… Function block diagrams (FBDs)
… Structured text (ST)
… Instruction List (IL)
… Sequential function charts (SFCs)
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Anatomy of a Ladder Program
- Input instructions are entered on the left
- Output instructions are entered on the right
- The power rails simulate the power supply lines
L1 and L2 for AC circuits and +24 v and ground for DC circuits
- Most PLCs allow more than one output per rung
- The processor (or “controller”) scans ladder rungs from top-to-bottom and from left-to-right.
The basic sequence is altered whenever jump or subroutine instructions are executed.
- PLC programming is a logical procedure
- In a PLC program, “things” (inputs and rungs) are either TRUE or FALSE
If the proper input conditions are TRUE:The rung becomes TRUE and an output action occurs (for example, a motor turns on)
If the proper input conditions are not TRUE:The rung becomes FALSE and an output action does not occur
- Ladder logic is based on the following logic functions:
AND, OR, Sometimes called “inclusive OR”, Exclusive OR.
For much more download here (PLC Downloads -> Usefull PLC PDF's -> Ladder Logic Fundamentals PLC tutorial).