I am looking for details on how redundancy works in S7-400 H System. I want to know about all the events that will cause data updating from master station to the slave station and likewise. What is the switching time required?

THANKS

 

Go to Siemens website
http://www4.ad.siemens.de/csinfo/li....csinfo&wttree=productnodes=en&objID=4000024 and look for H-systems manual as what you are asking for is a very deep topic.

Regards,

Jacek Dobrowolski, Ms. Sc. E. E.
Software Engineer

 

In fact, the slave PLC is running synchronised with the master PLC, not waiting on any events to update. In order to make this possible there are two fibre optic connections between the two PLC's (these are both needed, not redundant, if one connection fails, the slave goes to stop). The program is executed simultanious, the inputs are read by both PLC's all the time, the only difference is that the outputs are only written by the master PLC. Switchover of redundant ET200 stations (2 x IM153-2, non redundant IO cards) occurs within a few hundered milliseconds, without process interuption. Redundant IO is also possible for very high availability.

 

Hello CJOHN;

Jacek is right: the topic is very deep and sometimes murky. But your question needs some rephrasing: the update between primary and stand-by CPUs is continuous in the S7-400H. The specialized CPUs (414-H and 417-H) have a dedicated interface (fiber-optic) to link the CPUs and exchange input and output tables at every cycle, so both CPUs memories are consistent and always up-to-date. A discrepancy between the 2 image tables is one of the events that will trigger the change-over to stand-by. Program execution is also one of the events evaluated by the special program.

To make the Siemens redundant system work, you need the specialized CPUs, dedicated function blocks to monitor the state of the CPUs and trigger changeovers, and special hardware to establish redundancy at the I/O level on Profibus-DP (called a Y-Link) so that each CPU can request updates from the field during its sdcan cycle.

Hope this helps,
Daniel Chartier