Mitsubishi MELSEC QS Series, User Manual

Page: 186 / 264

9
DEVICE EXPLANATION
9
- 20 9.2 Internal User Devices
9.2.8 Timer (T)
(6) Retentive timers
(a) Definition
Retentive timers measure the "coil ON" time.
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.
(b) Retentive timer types
There are 2 retentive timer types: low speed retentive timer, and high speed
retentive timer.
(c) Retentive timer clear
The RST ST instruction is used to clear (reset) the current value and switch the
contact OFF.
(d) Measurement units
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
POINT
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.
Diagram 9.20 Ladder example and timing chart of retentive timer
X102
RST ST0
X100
ST0
K200
OFF
OFF
ON
ON
ON
X100
OFF
OFF
0 1 0
X102
150
ON
X100 ON time is measured as 20 seconds
when the timer measures time in 100 ms units.
Retentive timer display
When X102 switches ON, the ST0 contact is
reset, and the current value is cleared.
[Ladder example]
[Time chart]
ST0 coil
RST ST0 instruction
ST0 contact
ST0 present value
15s 5s
Present value is saved
when coil switches.
Contact remains ON when coil switches. Instruction execution
151 to 200
to