Phoenix Contact 2702924, User Manual

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Safety of machines and systems
102597_en_03 PHOENIX CONTACT
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2.2.2 Determination of the required performance level (PL
r
)
The PL
r
is determined in combination with the safety function within the framework of the
higher-level risk assessment. For each safety function, the required PL
r
is estimated using
the risk graph below.
Figure 2-2 Risk graph (in accordance with EN 13849-1)
Meaning of individual parameters:
2.2.3 Technical implementation
This step involves the technical pre-planning of the safety function, taking possible technol-
ogies and components into account. The safety-related components and parts must then
be identified for later verification.
Dividing the safety function into subsystems
In the next step, a safety-related block diagram must be created for further evaluation. As a
rule, a safety function consists of sensor - logic - actuator. In the simplest case, each one is
a subsystem. These subsystems are connected in series to form the overall safety function.
S: Severity of injury
S1 Slight (normally reversible) injury
S2 Serious (normally irreversible) injury
F: Frequency and duration of exposure to the hazard
F1 Seldom to not very frequent or exposure to hazard is brief
F2 Frequent to continuous or exposure to hazard is long
P: Possibility of avoiding or limiting damage
P1 Possible under specific conditions
P2 Scarcely possible
P1
P2
P1
P2
P1
P2
P1
P2
F1
F2
F1
F2
S1
S2
a
b
c
d
e
Low risk
High risk
Start
Required
performance level