Siemens Simatic S7 Series Manual page 56

SIMATIC Off-Delay Timer
(TOF)
The.SIMATIC Off-Delay Timer (TOF).begins.timing.when.input
(IN).turns.off..In.the.following.example,.when.contact.I.4.
closes,.the.current.value.of.timer.T33.is.set.to.0,.timer.bit.T33.
turns.on.immediately,.closing.the.T33.contact,.and.turning.on.
output.Q2.3.
When.contact.I.4.opens,.the.timer.times.until.the.preset.time.
elapses,.200.ms.in.this.example..Then,.timer.bit.T33.turns.off,.
contact.T33.opens,.and.output.Q2.3.turns.off.
If.the.I.4.contact.had.closed.again.before.the.200.ms.preset.
time.had.elapsed,.the.timer's.current.value.would.again.be.set.
to.0,.timer.bit.T33.would.remain.on,.contact.T33.would.remain.
closed,.and.output.Q2.3.would.remain.on.
Network 1
I1.4
Network 2
T33
55
T33
TOF
IN
10 ms
PT
+20
Preset time = 20 x 10 ms = 200 ms
Q2.3