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Description of devices
(2) Present value update timing and accuracy in refresh system
1) The timer accuracy is +2 scan times independently of the used timer and scan
time.
2) The following shows the present value update timing and accuracy when the
10ms timer is used in a program where the scan time is 10ms or more.
Fig 3.17 Timer Timing Method
In Fig. 3.8, the time-out period of the 10ms timer T3 has the following errors.
*1 .......... 10ms timer error (+1 scan time)
*2 .......... Error produced by timer's input condition ON timing and OUT
T instruction's program position (+1 scan time)
The accuracy is +2 scan time (+0.05s in Fig. 3.8)
3) When the timer times out, its contact remains on until END even if the coil turns
off, and turns off at execution of the END instruction.
Ladder example
Timer timing method
T3 contact turns on 6s after X0 turns
on. (T3 is 10ms timer.)
OUT
T3
OUT
T3
OUT
T3
END END END END END
OUT
T3
END
Scan time 25ms
When external
input turns on
in hatched
range
*2
6000ms
*1
121 2
31212123
2
3
2 2
3
X0
T3 coil
T3 contact
10ms timer
timing
Timing set
at END
T3 present
value
OFF
OFF
ON
ON
ON
600 appears when monitored
on peripheral device.
25ms 25ms 25ms 25ms
OFF
1 scan
0
1 scan
0
0 3 3 3 2 5 597 2 599 599 3 602