6 safety manual, Table 14 – JUMO 14597 safetyM STB/STW Ex - Safety Temperature Limiter and Safety Temperature Monitor Operating Manual User Manual
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6.11.3 Contribution to risk minimization through the control system
The objective of compliance with the overall draft procedure for the machine is to achieve the safety objectives (see 4.1 in DIN
EN 13849-1). The draft of the SRP/CS to provide the required risk minimization is an integral part of the overall draft procedure
for the machine. The SRP/CS provides the safety function(s) with a PL that achieves the required risk minimization. Through the
provision of safety functions, either as an inherently safe part of the construction or as the control of a protective guard or pro-
tective device, the design of the SRP/CS is part of the risk minimization strategy. This is an iterative process and is depicted in
figures 1 and 3 in DIN EN 13849-1.
The features of each safety function (see section 5 in DIN EN 13849-1) and the required Performance Level must be described
and documented in the specification of the safety requirements.
In this part of DIN EN ISO 13849, the Performance Levels are defined in the form of the probability of a dangerous failure per
hour. Five Performance Levels (a to e) are specified with defined areas of the probability of a dangerous failure per hour (see ta-
ble).
Table 14:
Performance Level (PL)
Average probability
of a dangerous failure per hour 1/h
a
≥
10
-5
to < 10
-4
b
≥
3 Þ 10
-6
to < 10
-5
c
≥
10
-6
to < 3 × 10
-6
d
≥
10
-7
to < 10
-6
e
≥
10
-8
to < 10
-7
NOTE: in addition to the average probability of a dangerous failure per hour, further measures are required to achieve the PL.