Interfacing between safety and standard program blocks

[amberman]

Hi,

I am picking up a project started by a predecessor who is now out of contact. It is a Siemens S7-1515F PLC system - but the query is how you transfer code between safe and standard program tasks. For some reason the guy bought all I/O as safe I/O even though we only need a handful of safe channels. Is it a big deal to take the signals from the safety blocks and send them to the standard blocks for normal processing? I'm aware this can be an issue for some systems.

As you can tell I've had little experience with safe PLCs, certainly none with Siemens. At this stage though I am more concerned we have the right hardware, I can get the relevant programming training at a later date.

Thanks if you can help!

 

[RVaughan]

The safety program can read and write standard DBs, so transferring data is trivial.

The standard program can read safety inputs but cannot write safety outputs, for obvious reasons.

However, the safety I/O only interacts with the process image (I and Q memory tables) if there is a reference to the individual I/O card somewhere in the safety logic. For your "standard" input cards you could create a safety Function that uses an open contact to read one bit on each card and writes to a temp tag.

I99.0 ...............................#DoNothing
-[ ] -------------------------------------------( )

 

[L D[AR2P#0.0]]

Recommendation from Siemens: