On-Delay & Off-Delay Timers
Add time to your circuits. On-delay waits before turning on; off-delay lingers before turning off — and between them they cover most timing jobs.
Two kinds of delay
Timers add the dimension of time to a control circuit. The two you’ll use constantly are the on-delay and the off-delay — and the difference is exactly which edge they delay.
On-Delay (TON)
When the timer is energized, it waits the preset time, then turns its output on. When de-energized, the output drops immediately and the timer resets. "Delay before action."
- Use it for: a warning horn that sounds, then the motor starts a few seconds later. A pump that must prove flow for 5 seconds before a heater is allowed on. Letting one event settle before the next begins.
Off-Delay (TOF)
The output turns on immediately when energized, then when de-energized it waits the preset time before turning off. "Delay before stopping."
- Use it for: a cooling fan that keeps running for two minutes after the machine stops. A light that stays on a while after you leave. Anything that should linger after its trigger goes away.
How a timer works in a circuit
A timer is wired like a coil — its circuit completing is its input. You give it a letter, and contacts (or contactors) with that letter follow its delayed output, exactly like they follow a coil. The only difference from a plain relay is the delay between input and output.
What to take away
On-delay waits, then acts (delay before on). Off-delay acts now, then lingers (delay before off). Wire a timer like a coil, give it a letter, and contacts with that letter follow its delayed output. These two timers cover the large majority of timing you’ll ever need.
Now build it yourself
In the Sandbox, wire a switch to a Timer (set it to ON-delay, 3 seconds, letter "T"), then a Light controlled by a NO Contact assigned to "T". Energize, flip the switch, and the light comes on 3 seconds later. Shift-click the timer to switch it to OFF-delay and watch the behavior flip.
Open the Sandbox →