siemens saftey integrated

[step7]

hello,

this is to talk about siemens saftey integrated system, talk about what you know about it and how it works using dual channels and i think 2 seprate micros.

 

[JesperMP]

No, the dual channels and cpus is called an "H" (high availablity) system.
A safety integrated system is called an "F" system.
It is possible to combine F and H systems (in the S7-400 series).

I have heard how safety over ASi works, and I assume that safety over F CPUs and Profibus works principally the same.
Rather than having hardwired signals between the safety devices (E-Stops, light curtains, etc.) and safety relays, the CPU sends a coded message to the device, which in turn must respond with another coded message. If the CPU doesnt recieve a proper return message it turns off the output devices that the safety devices shall safeguard.

 

[Doug_Adam]

It does not use two micros, just one.
However, it solves its logic in both the bit logic section of the CPU as well as the word logic section, then compares the results, thus getting the equivelent of having two diverse CPUs solving the logic (two channel).
This contrasts to the Pilz method of getting the same result via the use of three different CPUs in their safety PLC (two channel, plus one just to be sure).

 

[JesperMP]

Seing Dougs post I realise that "step7" wasnt thinking about dual S7 CPUs but the dual channels/dual CPUs of a safety relay.

 

[automatic simatic]

ok wait now, can some one explain to me the F and H systems, whats the diffrence and how do they work, thanks

 

[JesperMP]

Hi "automatic",
check this previous thread: http://www.plctalk.net/qanda/showthread.php?t=13453