KROHNE H250 M9 Safet V2 EN - Manual (Page 4)

2
TERMS AND DEFINITIONS
4
H250 M9
www.krohne.com 06/2013 - 4000656702 MA H250-M9 SIL R03
Terms and definitions
Terms and definitions
DC
D
Diagnostic Coverage of dangerous failures
FIT Failure In Time (1x10 -9 failures per hour)
FMEDA Failure Modes, Effects and Diagnostic Analysis
HFT Hardware Fault Tolerance
Low demand mode Mode, where the frequency of demand for operation made on a safety-related
system is not greater than one per year and not greater than twice in the proof test
frequency.
PFD
AVG
Average Probability of Failure on Demand
SFF Safe Failure Fraction summarizes the fraction of failure, 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" subsystem (all failure modes are well defined); for details see
7.4.3.1.2 of IEC 61508-2.
Type B component "Complex" subsystem (all failure modes are well defined); for details see 7.4.3.1.2
of IEC 61508-2.
T[Proof] Proof Test Interval
MA_H250_M9_SIL2_R03_en_656702_PRT.book Page 4 Wednesday, June 26, 2013 9:08 AM