Industrial Engineer · phase 3 of 16 · noun
Scan Time
Elapsed time required for one controller execution cycle or one scheduled task pass.
The Explain card
- Plain English
- Scan time is how long one pass through the cycle takes. It goes up with more logic, more I/O, more network traffic and heavier instructions.
- Example
- A controller shows a scan time of 8 milliseconds with a maximum of 23. The maximum is the number that matters, because that is the pass where the input got missed.
- Why it matters
- A scan that grows past the watchdog faults the controller, and a scan that grows past a sensor's pulse width loses counts. Watch the maximum in the controller properties after every significant edit.
- Hook
- The machine can only react as fast as it can think.
Word knowledge
How the word is built, where it came from, and what it sits beside in memory.
In a sentence
The engineer monitors Scan Time while a high-speed counter task processes encoder pulses during conveyor commissioning.
Why these words
- scan Latin scandere, to climb, through Late Latin scandere, to analyze verse identifies the controller's systematic pass through its work
- time Old English tima, a period or duration names the measured quantity associated with the scan
Where it came from
- Origin
- English technical compound formed from scan and time
- Entered the language
- 1970s
- What changed
- Scan developed from analyzing poetic meter to examining items systematically, then became associated with repeated electronic and controller operations.
How it is spelled
- Pattern
- Scan follows the short-vowel consonant-doubling pattern in scanned and scanning.
- Pattern
- Time keeps a final silent e that marks the long i sound.
Spelled like
- plan
- run
- line
- drive
Broken into chunks
-
scan
- scanner
- scanning
-
time
- timer
- timing
What it sits beside
Same subject
- scan cycle
- task period
- watchdog timer
- input image
- output image
Same shape
- cycle time
- execution time
- response time
controller timing terms
- Scan Time
- task period
- watchdog timeout
PLC scan stages
- input update
- program execution
- output update
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.
