Vega VEGAFLEX 80 series Safety Manual - 9 Appendixb:termdefinitions
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9 Appendix B: Term definitions
VEGAFLEX 80 series • Two-wire 4 … 20 mA/HART
42960-EN-170410
9 AppendixB:Termdefinitions
SIL
Safety Integrity Level (SIL1, SIL2, SIL3, SIL4)
SC
Systematic Capability (SC1, SC2, SC3, SC4)
HFT
Hardware Fault Tolerance
SFF
Safe Failure Fraction
PFD
AVG
Average Probability of dangerous Failure on Demand
PFH
Average frequency of a dangerous failure per hour (Ed.2)
FMEDA Failure Mode, Effects and Diagnostics Analysis
FIT
Failure In Time (1 FIT = 1 failure/10
9
h)
λ
SD
Rate for safe detected failure
λ
SU
Rate for safe undetected failure
λ
S
λ
S
= λ
SD
+ λ
SU
λ
DD
Rate for dangerous detected failure
λ
DU
Rate for dangerous undetected failure
λ
H
Rate for failure, who causes a high output current (> 21 mA)
λ
L
Rate for failure, who causes a low output current (≤ 3.6 mA)
λ
AD
Rate for diagnostic failure (detected)
λ
AU
Rate for diagnostic failure (undetected)
DC
Diagnostic Coverage
PTC
Proof Test Coverage (Diagnostic coverage for manual proof tests)
T1
Proof Test Interval
LT
Useful Life Time
MTBF
Mean Time Between Failure
MTTF
Mean Time To Failure
MTTR
Mean Time To Restoration (Ed.2)
MRT
Mean Repair Time
MTTF
d
Mean Time To dangerous Failure (ISO 13849-1)
PL
Performance Level (ISO 13849-1)
Abbreviations