Standards; Abbreviations - JUMO Ex-i Safety Manual

5 Safety-related applications
5.9

Standards

The devices are developed and approved according to the following standards:
IEC/EN 61508-1:2011
IEC/EN 61508-2:2011
IEC/EN 61326-1:2006
IEC/EN 61326-3-2: 2006
5.10

Abbreviations

DC
D
DC
S
FIT
HFT

D

DD

DU

S

SD

SU
MTBF
PDF
avg
PFH
D
SFF
SIL
24
Diagnostic coverage of dan-
gerous failures
Diagnostic coverage of safe
failures
Failure in time
Hardware fault tolerance
Rate of dangerous failures
Rate of dangerous detected
failures
Rate of dangerous undetected
failures
Rate of safe failures
Rate of safe detectable failures Rate of safe detectable failures per hour
Rate of safe undetectable fail-
ures
Mean time between failures
Average probability of failure
on demand
Probability of a dangerous fail-
ure per hour
Safe failure fraction
Safety integrity level
Functional safety of electrical/electronic/programmable electronic
safety-related systems, Part 1: General requirements
Functional safety of electrical/electronic/programmable electronic
safety-related systems, Part 2: Requirements for electrical/elec-
tronic/programmable electronic safety-related systems
Electrical equipment for measurement, control and laboratory use
- EMC requirements
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
Diagnostic coverage of dangerous failures:
= 
DC /(
D DD DU
Diagnostic coverage of safe failures:
= 
DC /(
S SD SU
1 FIT = 1 failure/10
Hardware fault tolerance: the ability of a functional unit to
continue performing a required function in cases in which
fault or deviations exist
Rate of dangerous failures per hour
Rate of dangerous detected failures per hour
Rate of dangerous undetected failures per hour
Rate of safe failures per hour
Rate of safe undetectable failures per hour
Mean time between two failures
Average probability of dangerous failures of a safety function
on demand
Probability per hour of a failure for the safety function
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
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.
+ 
)
DD
+ 
)
SD
9
h