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(6) Retentive timer
(a) Definition
This timer measures the period of time during which the coil is on.
The timer starts time measurement when its coil is turned on, and when it times out, the contact is
turned on. Even if the timer's coil is turned off, the current value and the on/off status of the contact
are retained.
When the coil is turned on again, the measurement restarts from the retained current value.
(b) Retentive timer clear
The current value and the contact off status can be cleared with the RST ST instruction.
(c) Time increment setting
The time increment is set in the same manner as the corresponding low- or high-speed timer.
• Low-speed retentive timer: Low-speed timer
• High-speed retentive timer: High-speed timer
To use a retentive timer, set the points for it in the Device tab of the PLC parameter dialog box.
Figure 9.24 Ladder example and timing chart of a retentive timer
X1
RST ST0
X0
ST0
K200
OFF
OFF
ON
ON
ON
X0
OFF
OFF
0to10
X1
150
ON
X0 ON time is measured for 20s when unit of
the timer is 100ms.
Retentive timer
When X1 is turned on, ST0 contact is reset
and the current value is cleared.
[Ladder example]
[Timing chart]
ST0 coil
RST ST0
instruction
Contact of
ST0
Current value
of ST0
15s 5s
Current value is held even
if the coil is turned off.
Contact remains on even if the coil is turned off.
Instruction execution
151 to
200