Siemens SIPART PS2 Operating Instructions Manual page 277

Abbreviation Full term in English
SFF Safe Failure Fraction
SIL Safety Integrity Level
SIS Safety Instrumented System
SIPART PS2 with and without HART
Operating Instructions, 02/2016, A5E00074631-AB
B.2 Abbreviations for functional safety
Meaning
Proportion of safe failures:
Proportion of failures without the potential to bring the safety-
instrumented system into a dangerous or non-permissible func-
tional status.
The international standard IEC 61508 defines four discrete
Safety Integrity Levels (SIL 1 to SIL 4). Each level corresponds
to a range of probability for failure of a safety function. The
higher the Safety Integrity Level of the safety-instrumented
system, the lower the probability that it will not execute the
required safety functions.
A safety-instrumented system (SIS) executes the safety func-
tions that are required to achieve or maintain a safe status in a
system. It consists of sensors, logic unit/control system and final
controlling elements.
Abbreviations
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