PLC and Ladder Logic
[PPT]Programming PLCs using LADDER Logic
Review of Ladder Programming
Keyence PLC Ladder Builder
Example 1: Motor Control
Example 2: Drill Control
Example 3: Traffic Light
Ladder Logic Diagrams
Diagrams
Sequential Function Charts
Instruction ListFunction Block
Structured Text
High-Level Language
[PPT]Introduction to IEC1131-3 Ladder Diagram
Origins of Ladder Diagram
The Ladder Diagram (LD) programming language originated from the graphical representation used to design an electrical control system
Control decisions were made using relays
After a while Relays were replaced by logic circuits
Logic gates used to make control decisions
Finally CPUs were added to take over the function of the logic circuits
I/O Devices wired to buffer transistors
Control decisions accomplished through programming
Relay Logic representation (or LD) was developed to make program creation and maintenance easier
Computer based graphical representation of wiring diagrams that was easy to understand
Reduced training and support cost
What is a Rung?
A rung of ladder diagram code can contain both input and output instructions
Input instructions perform a comparison or test and set the rung state based on the outcome
Normally left justified on the rung
Output instructions examine the rung state and execute some operation or function
In some cases output instructions can set the rung state
Normally right justified on the rung
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