PLC glossary
One-shot
A TRUE pulse lasting one scan when a signal changes. It turns one physical event into one countable request.
- Also called
- one shot, edge pulse
- On site
- One bottle under a sensor produces one arrival pulse, rather than a count on every scan.
- Siemens
- R_TRIG/F_TRIG or P/N edge instructions, depending on the language.
- Rockwell
- ONS/OSR/OSF in Ladder; OSRI or explicit input-history logic in the supported ST exercises.
Taught in: Count events, not scans
Practise it on a 3D rig
- Count the arrivalsCount each bottle once. Stop at three.
- Count with a one-shotOne bottle covers the sensor for many scans. Count it once.
- Count bottles as they leaveCount each bottle as it clears the sensor, not as it arrives.
- It never reaches threeSomething keeps clearing the count. Find it.
- Review the AI: One bottle, one countCheck a bottle that stays under the sensor.