2 - Schneider Electric CZ, s.r.o.

Presentation
Machine safety
Functional Safety of Machinery
Standard EN/IEC 62061
Select the applicable standard
Standard EN/IEC 62061
Machinery safety - Safety-Related Electrical Control systems (SRECS)
Process (continued)
> > Types of sub-system architecture
Sub-system element 1
Sub-system type A
Sub-system element n
1
Sub-system element 1
Sub-system element 2
Sub-system type B
Common cause failure
2
Sub-system element 1
Sub-system element n
Diagnostic function(s)
Sub-system type C
Sub-system element 1
Diagnostic function(s)
Sub-system element 2
Sub-system type D
Common cause failure
3
Stage 4 - Select the components for each sub-system
As the safety integrity level required in the example mentioned above is SIL 2, each
of the components must achieve this level.
Once the targeted SIL is determined, the components constructing the system
from safety-related sub-systems (sensor/switch, logic, actuator) have to be
selected. The components must have PFH d
(probability of dangerous failure per
hour) equal to the required SIL rating needed.
Stage 5 - Design the diagnostic function
The SIL of the sub-system depends not only on the components, but also on the
architecture selected.
In EN 62061, a safety integrity requirement is expressed as a target failure value for
the probability of dangerous failure per hour (PFH d
) of each safety related control
function (SRCF).
This can be calculated from reliability data for each component or sub-system, and
is related to the SIL as shown in Table 3 of the standard:
Relationship between SIL and PFH d
values
SIL Probability of dangerous failures per hour (PFH d
)
3 u 10 -8 ... < 10 -7
2 u 10 -7 ... < 10 -6
1 u 10 -6 ... < 10 -5
For each of the four logical architectures A to D presented above, there is a different formula
to calculate the PFH d
. The calculation method is complex and will not be presented here
(please see EN/IEC 62061 for the formula and the parameters taken into account).
Select the applicable standard
In order to be able to select the applicable standard, a common table in both
standards gives indications which are summarised in the table below:
Technology used EN ISO 13849-1
max. PL
EN/IEC 62061
max. SIL
Non electric only, e.g...hydraulic e Not covered
Including some electromechanical, .
e (for designated 3
for example relays and/or non complex electronics architectures only)
Including complex electronics, .
d 3
for example programmable
For building specific complex sub-systems or for higher level requirements
including software, standard EN/IEC 61508 relating to systems must be used.
Relationship between the performance level (PL) and the Safety
Integrity Level (SIL)
PL SIL Probability of dangerous failures per hour 1/h
a No correspondance u 10 -5 … < 10 -4
b 1 u 3 x 10 -6 … < 10 -5
c 1 u 10 -6 … < 3 x 10 -6
d 2 u 10 -7 … < 10 -6
e 3 u 10 -8 … < 10 -7
4
5
6
7
8
9
10
Typically for hoisting applications use standard EN ISO 13849-1.
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