Basic HTML Version
25
Combination or series connection of SRP/CS to achieve an overall performance level
PL a, b, c, d or e PL a, b, c, d or e
User design
Using certified
components
Interim results,
logic
PL
Determined by the machine manufacturer
Specified by the manufacturer
Logic
PL a, b, c, d or e PL a, b, c, d or e
User design
Using certified
components
Interim results,
actuators
PL a, b, c, d or e PL a, b, c, d or e
User design
Using certified
components
Architecture
selection
Diagnostic
coverage
0 ... 99%
CCF value
Common Cause
Failure
MTTF
d
B10 value
Application
data n
op
Architecture
selection
Diagnostic
coverage
0 ... 99%
CCF value
Common Cause
Failure
MTTF
d
B10 value
Application
data n
op
Architecture
selection
Diagnostic
coverage
0 ... 99%
CCF value
Common Cause
Failure
MTTF
d
B10 value
Application
data n
op
Interim results,
sensors
Sensors
Actuators
Safety functions can be
implemented using multiple
SRP/CS connected in series. The
performance of each SRP/CS is
either determined by the user or,
ideally, specified by the
manufacturer of the component
in the technical data for the
certified components.
The lowest performance level
must be determined to establish
the overall performance level,
which in turn has to be
determined based on the
standard for the overall PL.
Simplified procedure for
determining the PL for
components with PL
For series connection, the
number of the lowest PL is
determined. This result can be
used to determine the overall PL
using the table.
Lowest PL
Number of the lowest PL
Total system
PL low
N low
PL
a
,
3
Not permitted
≤3
a
b
,
2
a
≤2
b
c
,
2
b
≤2
c
d
,
3
c
≤3
d
e
,
3
d
≤3
e