Siemens SIMATIC ET 200AL System Manual page 138

Glossary
Safe Direction (SDI)
The SDI function (Safe Direction) monitors the direction of the motion.
Safe Operating Stop (SOS)
The SOS function (Safe Operating Stop) protects from unintentional motions.
Safe state
The basic principle of the safety concept in F-systems is the existence of a safe state for all
process variables. For the digital F-I/O, for example, the safe state is the value "0".
Safety class
Safety level (Safety Integrity Level) SIL according to IEC 61508:2010. The higher the Safety
Integrity Level, the more rigid the measures for prevention of systematic faults and for
management of systematic faults and hardware failures.
The fail-safe modules support operation in safety mode up to safety class SIL3.
Safety frame
In safety mode, data are transferred between the → F-CPU and → F-I/O in a safety frame.
Safety function
A mechanism integrated in the → F-CPU and → F-I/O that enables their use in → the fail-safe
system SIMATIC Safety.
According to IEC 61508:2010: A safety function is implemented by a safety system in order to
maintain or force a system safe state in the event of a specific fault.
Safety Limited Speed (SLS)
The SLS function (Safely Limited Speed) monitors the calculated speeds in both directions.
Safety mode
Operating mode of → F-I/O that enables → safety-related communication via → safety
frames.
The → fail-safe modules ET 200AL are designed for safety mode only.
Safety program
Safety-related user program
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Distributed I/O system
System Manual, 08/2021, A5E31861578-AJ