TOF — Off-Delay Timer

TOF

Timer

timer

(EN)

Preset

?

(DN)

Accum

?

Off-delay timer. Starts timing when the rung goes false; holds .DN at 1 for the preset duration after the rung drops.

Operands

Name	Type
timer	TIMER

How It Works

Rung state	.EN	.TT	.ACC	.DN
True	1	0	0	1
False, .ACC < .PRE	0	1	counting up	1
False, .ACC ≥ .PRE	0	0	holds at .PRE	0

While the rung is true, the timer is "primed" — .DN is 1 with zero elapsed time. When the rung drops, .DN stays 1 and the accumulator counts up. When .ACC reaches .PRE, .DN finally goes 0.

Example — Exhaust Fan Run-On

Keep an exhaust fan running for 30 seconds after the machine stops.

Tag setup: ExhaustTimer is a TIMER with .PRE = 30000.

XIC(MachineRunning)TOF(ExhaustTimer);XIC(ExhaustTimer.DN)OTE(ExhaustFan)

ExhaustFan stays on while the machine is running and for 30 seconds after it stops.

Common Mistakes

• Expecting TOF to start timing when the rung goes true — it is the opposite. TON times on rising edge, TOF on falling edge.

Related

• Timers overview — members, units, shared behaviour
• TON — on-delay counterpart
• RTO — retentive timer