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Glossary
11 .11 Diagnostic coverage DC
Measure of the effectiveness of diagnostics, which may
be determined as the ratio between the failure rate of
detected dangerous failures and the failure rate of total
dangerous failures
NOTE: Diagnostic coverage can exist for the whole or
parts of a safety-related system. For example, diagnos-
tic coverage could exist for sensors and/or logic system
and/or final elements. Unit: %.
from EN ISO 13849-1:2008
11 .12 Operating mode
High demand mode or continuous mode
Operating mode, where the frequency of demands for
operation made on a safety-related system is greater
than one per year or greater than twice the proof-test
frequency
from EN 61508-4:2001
11 .13 Safe failure fraction SFF
Fraction of safe failures related to all failures, which are
assumed to appear
from EN 13611/A2:2011
11 .14 Probability of dangerous failure PFH
Value describing the likelihood of dangerous failure per
hour of a component for high demand mode or con-
tinuous mode. Unit: 1/h.
from EN 13611/A2:2011
11 .15 Mean time to dangerous failure
MTTF
Expectation of the mean time to dangerous failure
from EN ISO 13849-1:2008
Ordering Information: Part No. KR2834
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