Pilz PNOZ Seies Configuration Manual page 283

Standards and directives
Safety-related parts of control systems - General principles for
design in accordance with EN ISO 13849-1
Safety-related parts of control sys-
tems – General principles for design
in accordance with EN ISO 13849-1
As the successor standard to EN 954-
1, EN ISO 13849-1 is based on the fa-
miliar categories. Equally, it examines
complete safety functions, including
all the components involved in their
design. EN ISO 13849-1 goes beyond
the qualitative approach of EN 954-1
to include a quantitative assessment
of the safety functions. A performance
level (PL) is used for this, building upon
the categories.
Components/devices require the fol-
lowing safety parameters:
Category (structural requirement)
PL: Performance level
MTTFd: Mean time to dangerous
failure Mean Time To Dangerous
Failure)
DC: Diagnostic coverage Diagnos-
tic Coverage)
CCF: Common cause failure Com-
mon Cause Failure)
The standard describes how to calcu-
late the performance level (PL) for
safety-related parts of control sys-
tems, based on designated architec-
tures. EN ISO 13849-1 refers any
deviations to IEC 61508.
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S a f e t y - r e l a t e d p a r t s o f c o n t r o l s y s t e m s - G e n e r a l p r i n c i p l e s f o r d e s i g n i n a c c o r d a n c e w i t h E N I S O 1 3 8 4 9 - 1 6 . 1 2 0 0 7 - 0 2 S t a n d a r d s a n d d i r e c t i v e s S a f e t y - r e l a t e d p a r t s o f c o n t r o l s y s t e m s - G e n e r a l p r i n c i p l e s f o r d e s i g n i n a c c o r d a n c e w i t h E N I S O 1 3 8 4 9 - 1
Risk assessment in accordance
with EN ISO 13849-1
Risk assessment is an iterative proc-
ess, i.e. it will need to be carried out
more than once. The risk must be esti-
mated and the performance level de-
fined for each hazard on which the risk
is to be reduced through control
measures. The risk is estimated
through consideration of the severity
of injury (S), the frequency and dura-
tion of exposure to the hazard (F) and
the possibility of avoiding or limiting
the harm (P).
Parameters S, F and P are used on the
risk graph to determine the required
performance level (PL ) for a safety
r
function. The selection of parameters
is no different to the procedure used in
EN 954-1 (1996). However, the result
is no longer a category but a PL.
6.1
2007-02
6.1-7