User Documentation

52555600000/02/05-2018
Scope and denitions
Device type A (simple subsystem):
The failure modes of all constituent components are
well dened and the behaviour under fault condi-
tions can be completely determined.
FMEDA(FailureMode,E󰀨ectsandDiagnostic
Analysis):
Systematic way to identify and evaluate the e󰀨ects
of di󰀨erent component failure modes, to determine
what could eliminate or reduce the chance of failure,
and to document a system in consideration.
Failureratesλ:
λ
SD
Total failure rate for safe detected failures
λ
SU
Total failure rate for safe undetected failures
λ
DD
Total failure rate for dangerous detected fail-
ures
λ
DU
Total failure rate for dangerous undetected
failures
MTTF (Mean Time To Failure):
Mean time between two failures. MTTF is a basic
measure of reliability for non-repairable systems.
Proof-test interval (T
proof
):
Interval between periodic tests performed to detect
failures in a safety-related system.
De-energised To Safe (DTS):
Safety-related switch-o󰀨
Energised To Safe (ETS):
Safety-related switch-on