27
Operation Manual
b maXX safe PLC
BMC-M-SAF-02
Document no.: 5.07020.04
5
F
UNCTIONAL
S
AFETY
This chapter describes parameters in relation to functional safety. First of all, in accor-
dance with IEC 61508, safety means that a system is free of unwarranted risks. Function-
al safety is the part of the overall 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.
The user can decide on setting the safety control in safety applications with a proof test
interval of 10 years or 20 years. Different safety characteristic values apply depending on
this.
5.1
Safety-related parameters for 20 years of operation
The safety-related parameters of the b maXX safe PLC will be described in the following
Safety-related parameters of local I/O terminals and decentral components can be found
in the applicable documentation. The values specified here relate exclusively to the PLC.
Parameters in accordance with
IEC 61508
Meaning
PFH = 2.23 * 10
-9
/h
Probability of Failure per Hour
PFD
avg
= 1.91 * 10
-4
Probability of Failure on Demand
= mean residual error probability of a dangerous
error on demand
SFF according to SIL 3
Safe Failure Fraction = fraction of failures which
lead to a safe status.
Parameters in accordance with
DIN EN ISO 13849
Meaning
MTTF
d
> 100 years
Mean Time To Failure
DC
avg
according to SIL 3
Diagnostic Coverage
Summary of Contents for b maXX BMC-M-SAF-02
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