Siemens SIPART PS2 Series Operating Instructions Manual page 323

Abbreviation Full term in English
SFF Safe Failure Fraction
SIL Safety Integrity Level
SIS Safety Instrumented System
SIPART PS2 with 4 to 20 mA/HART
Operating Instructions, 11/2019, A5E00074631-AE
G.2 Abbreviations for functional safety
Meaning
Proportion of safe failures:
Proportion of failures without the potential to bring the safety-in‐
strumented system into a dangerous or non-permissible func‐
tional status.
The international standard IEC 61508 defines four discrete Safe‐
ty 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 low‐
er the probability that it will not execute the required safety func‐
tions.
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
323