Safety integrity
6.4.
Various levels of safety integrity can be achieved depending on the type of integration. These are summarized
in Table 2 - Safety integrity when integrating generation of the warning signal as a safety function and Table 3 -
Safety integrity when integrating monitoring of the optical warning signal as a safety function.
Value
Warning signal
as safety function
Warning signal
as safety function
+
Monitoring function
Warning signal
as safety function
+
Monitoring function
+
Test of the monitoring function
prior to request
PFD* (T1=1
year)
1.11E-3
1.82E-4
7.93E-5
PFH [1/h]
2.54E-7
4.15E-8
1.8E-8
MTTF
d
[a]
>100
>100
>100
DC [%]
0
85.2
93.6
SFF [%]
70.2
96.5
98.5
SIL**
1
2
2
PL
c
d
d
*
Calculation applies for a repeat test interval of T1 = 8760h and MRT=MTTR=1h
**
The safety integrity level already accounts for the limitations inherent to the 1001 architecture, the classification
as a type B system and the requirements for avoiding systematic errors
Table 2 - Safety integrity when integrating generation of the warning signal as a safety function
Value
Monitoring function as a safety function
Monitoring function as a safety function
+
Test of the monitoring function
prior to request
PFD*
(T1=1Jahr)
1.16E-4
1.32E-5
PFH [1/h]
2.65E-8
3.01E-9
MTTF
d
[a]
>100
>100
DC [%]
0
88.6
SFF [%]
92
99.1
SIL**
2
2
PL
c
d
*
Calculation applies for a repeat test interval of T1 = 8760h and MRT=MTTR=1h
**
The safety integrity level already accounts for the limitations inherent to the 1001 architecture, the classification
as a type B system and the requirements for avoiding systematic errors
Table 3 - Safety integrity when integrating monitoring of the optical warning signal as a safety function
Limitations to safety integrity in terms of the achieved PFH and PFD can be found in tables 2 and 3 of
DIN EN 61508-1, while those related to the architecture and necessary SFF can be found on table 3 of
DIN EN 61508-2. Due to the measures that are used and the processes to avoid systematic failure, the safety
integrity level is limited to SIL2.
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