Timer instructions
324
Part II IEC Instructions
TOF
Timer with switch-off delay
To add an enable input and enable output to the instruction, select [With EN/ENO] from the
"Instructions" pane (LD, FBD or IL editor). To reuse an instruction select "Recently used" from the
context menu or press <Ctrl>+<Shift>+<v> in the programming window.
For TOF declare the following:
IN timer ON
an internal timer is started if a falling edge is detected at IN. If a rising edge is
detected at IN before PT has reached its value, Q will not be switched off (see
time chart, section
2
)
PT switch-off delay
(16-bit value: 0 - 327.27s, 32-bit value: 0 - 21,474,836.47s; resolution 10ms
each) the switch-off delay is defined here (PT = preset time)
Q signal output
is reset if PT = ET
ET elapsed time
represents the current value of the elapsed time
Time
chart
t
0
t
1
+ PT t
2
t
5
+ PT
t
0
t
1
t
2
t
3
t
4
t
5
IN
Q
ET
PT
t
0
t
1
t
2
t
3
t
4
t
5
1 2
1
Q is switched off with a delay corresponding to the time defined in PT. Switching on is
carried out without delay.
2
If IN (as in the time chart on top for t3 to t4) is set prior to the lapse of the delay time PT, Q
remains set (time chart for t2 to t3).
PLC types Availability of TOF (see page 1332)
Description
The function block TOF allows you to program a switch-off delay, e.g. to switch off the ventilator of
a machine at a later point in time than the machine itself.
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