Glossary · Automation fundamentals, platforms and components
On-delay (TON)
Also known as: On-delay timer, TON
German: Einschaltverzögerung
In IEC 61131-3, an on-delay is a timer function (standard function block TON) whose output becomes true only after its input has been true continuously for the preset time; the output resets immediately when the input becomes false.
- Automation components
- Standards
In one sentence
An on-delay (TON) timer sets its output only after its input has been true for the preset time and resets it at once when the input drops.
Example
A level switch must report "full" for 2 s before the pump stops, so waves in the tank do not cause rapid switching.
How it applies
- Engineering: On-delays filter short signals, confirm stable states and create time-based sequences. The timer resolution depends on the task cycle.
- Commissioning: Preset times are often tuned on site and should be recorded.
- Documentation: Parameter lists should give preset times, units and adjustability. When delays affect how long a machine continues or waits before moving, describe that behavior in the operating instructions.
- Maintenance: Changing timer presets online alters machine behavior; such changes should follow change control.
On-delay vs. off-delay
An on-delay (TON) delays switching on. An off-delay (TOF) sets its output immediately and keeps it true for the preset time after the input drops. A pulse timer (TP) produces an output of fixed duration.