IntermediateOff-delay timer~12 min

Off-Delay Cooling Fan (TOF)

A heater's cooling fan must keep running for 3 seconds AFTER the heater stops the classic off-delay. One TOF timer does the whole job.

Your goal

  • While Heater is ON, the Fan runs.
  • When Heater turns OFF, the Fan keeps running for 3 more seconds, then stops.
  • If Heater comes back ON during the delay, the delay restarts from full next time.
Stuck? Show hints (3)
  1. TOF behaves opposite to TON: its DN bit goes TRUE the instant the rung is true, and STAYS true for the preset after the rung goes false.
  2. Rung 1: NO Heater → TOF Tc. Rung 2: NO Tc.DN → OTE Fan. That's the whole exercise.
  3. Watch the ACC bar in Run mode: it only counts while the rung is FALSE that's the delay running out.

Off-delay timing a staple of every real machine.

I/O for this exercise

Inputs
HeaterHeater running signal
Outputs
FanCooling fan
Timers
Tc · 3000msCool-down off-delay
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