Hello JoseMiguelZubi;

The best way to know the operating stats of a redundant S7-400H? Inside your PLC program, that would be using System function SC 51, with SSL-ID w#16#0071.

Have a look at this discussion, for starters:

https://support.industry.siemens.com/tf/ww/en/posts/s7-400h-how-to-distinguish-primary-secondary-cpu-is-running/148281/?page=0&pageSize=10

The first link proposed in tht thread proposes a solution, reading SFC 51 with SSL--ID w#16#0071 prgrammed in CFC, for PCS 7 programmers.:

- How do you read out the operating state and status of an H system?

https://support.industry.siemens.com/cs/ww/en/view/19537149

If you do not use PCS 7 CFC programming, the following application example uses the same SSL-ID w#16#0071 to determine the active primary CPU in a redundant pair, you can study the documentation and open the code to find the SFC 51 calling function.

- Realization of a Fault-Tolerant Tunnel Lighting System With S7-400H

https://support.industry.siemens.com/cs/ww/en/view/81066268

Hope this helps,

Daniel Chartier

Hello  JoséMiguelZubi;

OB 72 will be called whenever the H-CPU detects a switchover between primary and standby CPUs, so this would probably work for you.

When the switchover event is detected, the call to SFC 51 inside OB 72 will be executed.

See the attached pdf printout from the System and Sandard Functions manual.

Hope this helps,

Daniel Chartier