Software Redundancy of Siemens S7 PLC


Thread Starter

Sam Kwok

I'm looking for a inexpensive alternative to hot backup of Siemens PLC and somebody suggegst me to look for software redundancy. However, I'm also told that software redundancy is a lower grade solution for redundant PLC and the switchover time could be longer than 1.5 second!! Also there is a lot of software programming work to do just to take care of the transferring of data between the redundant PLCs. Can anybody that has experience with this system tell me what is it all about?

Don't know for sure about switchover time, but I do believe it's much faster than you think. Contact your Siemens Automation specialist and he/she should be able to help you.
I just quoted an S7-300 series redundant plcs using remote I/O with Redundant Profibus adapters; MPI and Modbus was used for distributed processing and data collection. This design did not use software redundancy.

Zan Von Flue

I haven't done this with a S7 series but with a S5 series PLC. I was lucky to have a ethernet card to transfer the information back and forth. I had the same main program run in both PLC's except a small change in the master and in the slave. Every time a DB was changed it would be taged and the master would send this to the slave and erase the tag.
If the master failed, the watchdog timer, the slave would deactivate the master (through relay's) and take over. As soon as the master is "ok", everything would stop. The slave would send every db to the master. After this the master would start over again. This is no safety system. A 400H series would automatically handle this.
This was also only a gateway, very little i/o's.

Miller, Chuck (IndSys, GEFanuc, NA)

You might be interested to take a look at GE Fanuc's approach to hot standby redundancy. The 90-30 Max-On package is very cost effective and easy to use. "Out of the box" features include synchronization of data, redundant communications and extensive diagnostics. Synchronization can take place over GENIUS Bus or Ethernet and switchover is typically less than 100 msec. In addition , there are three price levels (Max-On Lite, Standard and Extended) to choose from based upon I/O count and required functionality.

For additional information contact your local GE distributor, 1 800 GE Fanuc or contact me off-line

Chuck Miller
GE Fanuc Critical Control Business Leader
(281) 495-0333
Fax: (281) 495-0370
email: [email protected]

Marty Schindehette

Siemens offer a very competitve variety software and hardware redundancy at varies levels. In regards to your dilema I would suggest contacting.

Tim Parmer
Siemens Product Manager of Redundanct Products
Phone (770) 871-3926
e-mail: [email protected]