10 - 21 10 - 21
MELSEC-Q
10 DEVICES
Retentive timers
(1) Definition
(a) Retentive timers measure the "coil ON" time.
(b) The measurement begins when the timer coil switches ON, and the contact
switches ON when a time-out (coil OFF) occurs.
Even when the timer coil is OFF, the current value and the contact ON/OFF
status are saved. When the coil is switched ON again, the time
measurement resumes from the current value which was saved.
(c) There are 2 retentive timer types: low speed retentive timer, and high speed
retentive timer.
(d) The RST T
instruction is used to clear (reset) the current value and switch
the contact OFF.
X1
RST ST0
X0
ST0
K200
[Ladder example]
When X1 switches ON, the ST0 contact is reset, and
the current value is cleared.
X0 ON time is measured as 20 seconds when the timer
measures time in 100 ms units.
Retentive timer display
T0 coil
OFF
OFF
ON
ON
ON
15s
[Time chart]
X0
T0 present value
OFF
OFF
0to1 151 200to
5s
0
Contact remains ON when coil switches.
Present value is saved when coil switches.
X1
T0 contact
RST ST0 instruction
150
Instruction execution
ON
(2) Measurement units
(a) The measurement units settings for retentive timers are the same as those
for low speed timers and high speed timers.
• Low speed retentive timer: Same as low speed timer
• High speed retentive timer: Same as high speed timer
REMARK
In order to use retentive timers, a retentive timer "number of points used" setting
must be designated at the "Device" tab screen in the “(PLC) Parameter" dialog box.
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