Industrial Engineer · phase 3 of 16
Ladder Diagram (LD)
IEC 61131-3 graphical language that represents logic with relay-style contacts, coils, and function blocks.
The Explain card
- Plain English
- Ladder is the graphical language that draws logic the way an electrician draws a relay circuit. Two rails, rungs across them, contacts that test conditions and coils that set results.
- Example
- A rung with a normally open start contact in parallel with the motor's own run bit, in series with a normally closed stop contact, feeding the run coil. That is a seal in circuit, and every plant has a thousand of them.
- Why it matters
- Maintenance can read ladder at three in the morning with the machine down, because it looks like the schematic on the panel door. It is the language most of the installed base speaks, whatever the newer ones can do.
- Hook
- The wiring diagram that runs itself.
Where it sits in the deck
Phase 3: PLC Program Organization and Execution
How the logic is arranged and how the scan actually runs it, which is the difference between code that works and code that works every time.
