2017-09
18
Functional Safety HiD2022*, KFD2-STC5-(Ex)*, KFD2-STV5-(Ex)*
Planning
KFD2-STC5-1.2O, KFD2-STC5-Ex1.2O, KFD2-STC5-Ex1.2O.H,
KFD2-STV5-Ex1.2O-1, KFD2-STV5-Ex1.2O-2
The characteristic safety values like PFD, SFF, HFT and T
1
are taken from the
SIL report/FMEDA report. Observe that PFD and T
1
are related to each other.
The function of the devices has to be checked within the proof test interval (T
1
).
Parameters acc. to IEC 61508 Characteristic values
Assessment type and
documentation
FMEDA report
Device type A
Operating mode Low Demand Mode or High Demand Mode
Safety function Transfer of analog signals
HFT 0
SIL (SC) 2 3
Input and output function 1 output used in safety function 2 outputs used in safety function
s
1
1
"No effect failures" are not influencing the safety function and are therefore not included in SFF and in the
failure rates of the safety function.
0 FIT 0 FIT
dd
2
2
"Fail high" and "Fail low" failures are considered as dangerous detected failures
dd
.
177 FIT 328 FIT
du
3
3
The safety characteristic values were calculated considering a common cause factor of 5 % for the safety
relevant output part.
For the application with 2 outputs in the safety function, the ESD system needs to detect if the outputs differ
by more than 2 %.
57 FIT 9.3 FIT
not part
72 FIT 114 FIT
total (safety function)
234 FIT 337 FIT
total
660 FIT 954 FIT
SFF 80 % 97.3 %
PTC 100 % 100 %
MTBF
4
4
acc. to SN29500. This value includes failures which are not part of the safety function/MTTR = 24 h. The
value is valid for one safety loop only.
173 years 119 years
PFH
3
5.67 x 10
-8
1/h 9.27 x 10
-9
1/h
PFD
avg
for T
1
= 1 year 2.48 x 10
-4
4.06 x 10
-5
PFD
avg
for T
1
= 2 years 4.97 x 10
-4
8.12 x 10
-5
PFD
avg
for T
1
= 5 years 1.24 x 10
-3
2.03 x 10
-4
Reaction time
5
5
Time between fault detection and fault reaction
< 100 ms
Table 3.3
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