Eaton XC-303 Series - Page 86

4 PLC configuration
4.4 Task monitoring by watchdog
Modular PLCs XControl: XC-104-…, XC-204-…, XC-303-… 01/23 MN050005EN Eaton.com 81
The triggering of the watchdog continues to be dependant on the watchdog
sensitivity. The watchdog sensitivity determines when the watchdog will be
triggered, after the watchdog time has been exceeded by a determined num-
ber of consecutive occasions.
The watchdog is triggered:
• immediately when the watchdog time is exceeded with a watchdog sen-
sitivity of “1”,
• immediately after the “x”th consecutive time that the watchdog time is
exceeded with a watchdog sensitivity of “x”.
For example, a task with a watchdog time of “10 ms” and a watchdog sensi-
tivity of “5” will end at the latest after 5 x 10 ms = 50 ms.
Example: Watchdog active
The interaction of interval time (IZ), task run time (TZ), watchdog time (WT)
and watchdog sensitivity are illustrated by the following configuration exam-
ple:
• Watchdog on
• Watchdog time (WT) = 15 ms
• Watchdog sensitivity = 2
The interval time (IZ) of the task is 10 ms.
Variant a: The watchdog is not triggered as the task time always remains
below the defined watchdog time.
Variant b: The watchdog is triggered 15 ms after commencement of the
second task , as both times are longer than the defined watchdog time
and occur consecutively.
Variant c: The watchdog is triggered 15 ms after commencement of the
second consecutive task, which is longer than the defined watchdog time.
Variant d; Endless loop: The watchdog is triggered , because the task
time takes longer than the watchdog time multiplied by the watchdog sensi-
tivity (2 x 15 ms = 30 ms).
Figure 57: Watchdog active, multiple tasks with differing priority
Watchdog deactivated
The cycle time of a task is not monitored when the watchdog is deactivated.
The task will be terminated once it has been completed and will not be
started again until the next interval starts.
TZ < WZ TZ < WZ TZ < WZ
TZ > WZ TZ = WZ
TZ > WZ TZ < WZ TZ < WZ TZ > WZ TZ = WZ
IZ
IZ IZ IZ
IZ IZ
IZ IZ
IZ
IZ
a TZ < WZ
b TZ > WZ
c TZ k WZ
d TT > WT
(continuous
loop)
TZ > 2 x WZ
IZ = 10 ms