Allen-Bradley 1756-CNB/E, User Manual

Page: 100 / 186

Publication 1756-UM523F-EN-P - December 2006
100 Configure and Program the Controller
Set Task Watchdog Times
To give a redundant controller longer watchdog times than a
nonredundant controller, perform this procedure.
•
After a switchover, the secondary controller starts the scan at the
beginning of the program that was running in the primary
controller at the time of the switchover.
•
The watchdog timer for the task that has the program, however,
is not reset.
•
A major fault happens (type 6, code 1) if the watchdog timer has
too little time to completely rescan the program.
Action Details
1. Set the minimum watchdog time for a
task.
Use this formula to set the minimum watchdog time for a task:
Minimum watchdog time
=
(2 *
maximum_scan_time
) + 150 ms
where:
Maximum_scan_time
is the maximum scan time for the entire task when the
secondary controller is synchronized.
2. Set the estimated watchdog time for a
task.
C. Type a watchdog time that is
more than the watchdog time
from step 1.
B. Click Configuration.
D. Choose OK.
Controller Primary
Tasks
MainTask
+
−
+
A. Right-click the task and choose Properties.