APP -8 APP -8
PPENDICES
MELSEC-Q
APPENDIX 2.1 Step Transition Watchdog Timer Replacement Method
(1) Operation of step transition watchdog timer
The step watchdog timer measures the ON time of the special relay for step transition
watchdog timer start (SM90 to SM99), and when it exceeds the time set to the special register
for step transition watchdog timer setting (SD90 to SD99), the corresponding annunciator (F)
set to any of (SD90 to SD99) is turned ON.
The following figure shows a step transition watchdog timer program.
b15 b8 b7 b0
SD90
F No. setting
(0 to 255)
Timer time limit setting
(0 to 255s)
(1s unit)
S0
S1
S2
S3
oSM90
ON while active.
Turns OFF when transition
condition is satisfied.
(2) Step transition watchdog timer replacement method
When performing the same operation as that of the step transition watchdog timer, create the
following program at the operation output.
S1
S2 oF0
aT0
S3
t1
t3
t2
t4
oT0 Km m: Watching time (unit: 10ms)
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