Fail-Safe Systems
A5E00085588-03
3-1
3 Safety Mechanisms
3.1 Introduction to the Safety Mechanisms
This chapter describes the safety-related mechanisms of the S7 F/FH Systems.
This information serves as background knowledge when you configure the F-
System and create and test the Safety Program. Only the functions in which the
behavior of an S7 F System differs from that of a standard S7 system are
described. The standard behavior is described in the STEP 7 and hardware
manuals.
Which Safety Mechanisms Are Relevant to You?
The safety-related mechanisms in the CPU (hardware and operating system) are:
• Access protection for F-Systems – which helps to avoid faults
• Self-tests – which help to detect and identify faults
The safety-related functions for fault detection and fault reaction are mainly located
in the Safety Program and in the F-I/Os. These functions are implemented by
means of appropriate fail-safe blocks and supported by the hardware and the CPU
operating system.
The safety-related functions of the F-I/Os are described in manual /1/. (Please
refer to the references in Appendix B.)
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