2
02
1-
04
16
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
Full assessment
Device type
A
Operating mode
Low Demand Mode or High Demand Mode
Safety function
Transfer of analog signals
Input and output function
1 output used in safety function
2 outputs used in safety function
HFT
0
SIL
2
3
SC
3
s
0 FIT
0 FIT
low
1
1
"Fail low" failures are considered as dangerous detected failures
dd
.
177 FIT
328 FIT
du
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
2
2
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
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 %.
5.67 x 10
-8
1/h
9.27 x 10
-9
1/h
PFD
avg
for T
1
= 1 year
3
2.48 x 10
-4
4.06 x 10
-5
PFD
avg
for T
1
= 2 years
3
4.97 x 10
-4
8.12 x 10
-5
PFD
avg
for T
1
= 5 years
3
1.24 x 10
-3
2.03 x 10
-4
Reaction time
4
4
Time between fault detection and fault reaction
< 100 ms
Table 3.3
