Rockwell Automation 1785-CHBM ControlNet PLC-5 Hot Backup System User Manual - Manual (Page 98)

Publication 1785-UM024B-EN-P - January 2003
B-18 Backup States
– Problems with the ControlNet network which causes loss of
the handshake connection with the primary processor.
The formula that determines the length of time the secondary
system waits before timing out the primary processor is as
follows:
Primary Timeout = 5 + (3 * NUT) or 25ms, whichever is
greater.
So, if the NUT is 5ms, the Primary Timeout is 25ms. If the NUT is
10ms, the Primary Timeout is 35ms.
The Primary Timeout is not the only factor in the Timeout
Switchover Time. There is also processing which must occur on
the secondary system after a Primary Timeout occurs. This
processing can take up to 5ms. The formula for the Timeout
Switchover Time is:
Timeout Switchover Time = Primary Timeout + 5ms.
So, if the NUT is 5ms, the Timeout Switchover Time is equal to
25ms plus 5ms, or 30ms.