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Operation Manual Safety I/O Terminals SI4000 / SO4000
Document no.: 5.08009.05
4FUNCTIONAL SAFETY
This chapter describes parameters in relation to functional safety. First of all, in accor-
dance with IEC 61508, safety means that a syste
m is free of unwarranted risks. Function-
al safety is the part of the o
verall safety, which ensures that a safety system’s response
to its input conditions is free of errors. Internal safety-related device errors must be de-
tected and brought into a safe condition in the process.
4.1 Safety-related parameters
The safety-related parameters of the safety I/O Terminals will be described in the follow-
ing Safety-related parameters of b maXX safe PLC and decentral components can be
foun
d in the applicable documentation. The values specified here relate exclusively to the
safety I/O Terminals.
Parameters in accordance with
IEC 61508
Meaning
PFH = 2.30 * 10
-9
/h for SI4000
PFH = 1.73 * 10
-9
/h for SO4000
Probability of Failure per Hour
PFD
avg
= 1.81 * 10
-4
for SI4000
PFD
avg
= 1.42 * 10
-4
for SO4000
Probability of Failure on Demand
= mean residual error probability of a dangerous
error on demand
Lifetime [a] = 20 years
Safety Integrity Level = SIL 3
Classification element *) type A
HFT 1 Hardware Failure Tolerance
*) Classification according to IEC 61508-2:2010 (see chapter 7.4.4.1.2 and
7.4.4.1.3 in IEC 61508-2)
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