Appendix B: Term Definitions - Siemens SITRANS LVL200H Safety Manual

Abbreviations
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9 Appendix B: Term definitions
SIL Safety Integrity Level (SIL1, SIL2, SIL3, SIL4)
SC Systematic Capability (SC1, SC2, SC3, SC4)
HFT Hardware Fault Tolerance
SFF Safe Failure Fraction
PFD Average Probability of dangerous Failure on Demand
AVG
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
λ Rate for safe detected failure
SD
λ Rate for safe undetected failure
SU
λ λ = λ + λ
S S SD SU
λ Rate for dangerous detected failure
DD
λ Rate for dangerous undetected failure
DU
λ Rate for failure, who causes a high output current (> 21 mA)
H
λ Rate for failure, who causes a low output current (≤ 3.6 mA)
L
λ Rate for diagnostic failure (detected)
AD
λ Rate for diagnostic failure (undetected)
AU
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 + MTTR
MTTF Mean Time To Failure
MTTR IEC 61508, Ed1: Mean Time To Repair
IEC 61508, Ed2: Mean Time To Restoration
MTTF Mean Time To dangerous Failure (ISO 13849-1)
d
PL Performance Level (ISO 13849-1)
SITRANS LVL200H - Safety Manual
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