JUMO Ex-i, Safety Manual

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6 Safety-related applications
6.16 Standards
The devices are developed and approved according to the following standards:
6.17 Abbreviations
IEC/EN 61508-1:2011 Functional safety of electrical/electronic/programmable electronic
safety-related systems, Part 1: General requirements
IEC/EN 61508-2:2011 Functional safety of electrical/electronic/programmable electronic
safety-related systems, Part 2: Requirements for electrical/elec-
tronic/programmable electronic safety-related systems
IEC/EN 61326-1:2006 Electrical equipment for measurement, control and laboratory use
- EMC requirements
IEC/EN 61326-3-2: 2006 Electrical equipment for measurement, control and laboratory use
- EMC requirements - Part 3-2: Immunity requirements for safety-
related systems and for equipment intended to perform safety-re-
lated functions (functional safety) - Industrial applications with
specified electromagnetic environment
DC
D
Diagnostic coverage of dan-
gerous failures Diagnostic coverage of dangerous failures:
DC
D
=

DD
/(

DU
+

DD
)
DC
S
Diagnostic coverage of safe
failures Diagnostic coverage of safe failures:
DC
S
=

SD
/(

SU
+

SD
)
FIT Failure in time 1 FIT = 1 failure/10
9
h
HFT Hardware fault tolerance Hardware fault tolerance: the ability of a functional unit to
continue performing a required function in cases in which
fault or deviations exist

D
Rate of dangerous failures Rate of dangerous failures per hour

DD
Rate of dangerous detected
failures Rate of dangerous detected failures per hour

DU
Rate of dangerous undetected
failures Rate of dangerous undetected failures per hour

S
Rate of safe failures Rate of safe failures per hour

SD
Rate of safe detectable failures Rate of safe detectable failures per hour

SU
Rate of safe undetectable fail-
ures Rate of safe undetectable failures per hour
MTBF Mean time between failures Mean time between two failures
PDF
avg
Average probability of failure
on demand Average probability of dangerous failures of a safety function
on demand
PFH
D
Probability of a dangerous fail-
ure per hour Probability per hour of a failure for the safety function
SFF Safe failure fraction Fraction of safe failures: fraction of failures that do not have
the potential of putting the safety-related system into a dan-
gerous or inadmissible functional state
SIL Safety integrity level The international IEC 61508 standard defines four discrete
safety integrity levels (SIL 1 to SIL 4). Each level corre-
sponds to a probability range for the failure of a safety func-
tion. The higher the safety integrity level of the safety-related
systems is, the lower the probability of the systems failing to
perform the required safety functions is.