Decommissioning and withdrawal from service
© exida.com GmbH TURCK 04-07-14 R001 V2R0.doc; February 8, 2013
Stephan Aschenbrenner Page 19 of 25
6 Terms and Definitions
DC
S
Diagnostic Coverage of safe failures (DC
S
= λ
sd
/ (λ
sd
+ λ
su
)
DC
D
Diagnostic Coverage of dangerous failures (DC
D
= λ
dd
/ (λ
dd
+ λ
du
)
FIT Failure In Time (1x10
-9
failures per hour)
FMEDA Failure Modes, Effects, and Diagnostic Analysis
HART Highway Addressable Remote Transducer
HFT Hardware Fault Tolerance
Low demand mode Mode, where the frequency of demands for operation made on a safety-
related system is no greater than one per year and no greater than twice
the proof test frequency.
PFD
AVG
Average Probability of Failure on Demand
SFF Safe Failure Fraction summarizes the fraction of failures, which lead to a
safe state and the fraction of failures which will be detected by
diagnostic measures and lead to a defined safety action.
SIF Safety Instrumented Function
SIL Safety Integrity Level
Type A component “Non-complex” component (all failure modes are well defined); for
details see 7.4.3.1.2 of IEC 61508-2.
T[Proof] Proof Test Interval
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