Basic HTML Version
11
When assessing risk and
identifying the necessary
performance level, the degree
of risk reduction is established.
Whether or not the required
risk reduction level has been
achieved depends on the
following parameters:
1) Control architecture
2) Mean time to dangerous
failure (MTTF d )
3) Diagnostic coverage (DC)
4) Common cause failures (CCF)
In all cases, the performance
level (PL) must be equivalent to
at least the required PL r .
Source: DIN EN ISO 13849-1, 4.2 Fig. 3
Source: EN 12100
Design measures
e.g. inherent safety
Technical safety measures and
complimentary safety measures
Selecting the safety function
Defining the characteristics of the safety function
Determining the PL r
Design and technical implementation
of the safety function
Determining the PL
Category
MTTF d
DC
CCF
User information on the machine and in the user
manual
PL PL r
Yes
No
Source: EN 12100
For all safety functions
Risk reduction
Source: EN ISO 12100