Vega VEGAFLEX 80, Safety Manual

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9 Appendix B - Term definitions
VEGAFLEX 80 series • 4 … 20 mA/HART - two-wire
42960-EN-140924
9 Appendix B - Term definitions
SIL Safety Integrity Level
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
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)
MTTF
d
Mean Time To dangerous Failure (ISO 13849-1)
PL Performance Level (ISO 13849-1)
Abbreviations