Industrial Engineer · phase 3 of 16 · noun
Rung
Horizontal network of conditions and instructions in ladder logic.
The Explain card
- Plain English
- A rung is one horizontal line of ladder logic between the two power rails. Conditions on the left decide whether power reaches the instructions on the right.
- Example
- Rung 14 has a limit switch contact and a timer done bit in series, feeding an output coil. If both are true, the coil is on for that scan.
- Why it matters
- Rungs are solved top to bottom, left to right, so where a rung sits changes when its result is available. A coil written on two different rungs takes the value of the last one, and that is one of the oldest bugs in the trade.
- Hook
- One line, one decision, evaluated every scan.
Word knowledge
How the word is built, where it came from, and what it sits beside in memory.
In a sentence
The technician added an overload contact to the motor-start rung before testing the PLC output coil.
How it is built
- rung root a crosspiece of a ladder
Where it came from
- Origin
- Old English hrung, related to Old High German runga
- Entered the language
- c. 1000
- What changed
- The physical ladder term was later applied to similarly shaped lines in electrical and control diagrams.
How it is spelled
- Pattern
- The final ng represents the single consonant sound /ŋ/.
- Pattern
- The letter u has its short /ʌ/ sound before ng.
Spelled like
- lung
- sung
- hung
Broken into chunks
-
rung
- rungs
- runged
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.
