Rockwell Automation 1755-OF8 GuardPLC Controller Systems - Manual (Page 192)

192 Publication 1753-UM001C-EN-P - March 2010
Chapter 17 Configure Peer-to-Peer Communication
Reconfigure Watchdog Time
To optimize the Watchdog Time to the lowest possible value, you
must know the maximum CPU cycle time. Cycle Time max., as
displayed on the Statistics tab of the Control Panel, is the value that
occurred so far, but is not necessarily the maximum value that can
occur depending on network and process conditions.
If the maximum Cycle Time cannot be estimated, run the project for
several hours and under as many conditions as possible.
Follow these steps to reconfigure the Watchdog Time.
1. In the project tree, right-click the first resource and choose
Properties.
2. Calculate a Margin of Safety, MoS:
MoS = 0.1 x (Cycle Time max.)
MoS should be at least 6 ms. If MoS < 6 ms, then
MoS = 6 ms
3. Readjust the Watchdog Time:
Watchdog Time = (Cycle Time max.) + (MoS)
In the example on the following page, the new Watchdog Time
is: 8 ms + 6 ms = 14 ms.