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Devices in Detail
Retentive timers
In addition to the normal timers described above, all controllers covered in this manual except
the FX
1S
the device controlling them is switched off.
The current timer counter value is stored in a memory that is retained even in the event of a
power failure.
Example of a program using a retentive timer:
Ladder Diagram
X1
0
T250
4
X2
6
Timer T250 is started when input X0 is switched on. The setpoint value is 345 x 0.1 s = 34.5s.
When the setpoint value is reached T250 switches output Y1 on. Input X2 resets the timer and
switches its output off.
X1
T250
Y1
X2
FX Beginners Manual
series also have retentive timers that retain their current time counter value even if
t1
t2
t1 + t2 = 34,5 s
K345
T250
Y1
RST
T250
When X1 is on the timer counts the internal
100ms pulses. When X1 is switched off the
current time counter value is retained. The
timer's output is switched on when the cur-
rent value reaches the setpoint value of the
timer.
A separate instruction must be programmed
to reset the timer since it is not reset by swit-
ching off input X1 or the PLC's power. Input
X2 resets timer T250 and switches off its
output.
Instruction List
0
LD
X0
1
OUT
T250
4
LD
T250
5
OUT
Y1
6
LD
X2
7
RST
T250
Timers
K345
4 – 7
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