20
20
-0
6
12
Functional Safety KFD2-SCD2-Ex*.LK, HiD2038
Planning
3.4
Characteristic Safety Values
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
Characteristic values
Assessment type
Full assessment
Device type
A
Mode of operation
Low demand mode or high demand mode
HFT
0
SIL
1
2
SC
3
Safety function
Transfer of the analog signals
s
0 FIT
dd
153 FIT
du
36.9 FIT
total (safety function)
190 FIT
SFF
80 %
MTBF
2
216 years
PFH
3.69 x 10
-8
1/h
PFD
avg
for T
1
= 1 year
1.62 x 10
-4
PFD
avg
for T
1
= 2 years
3.23 x 10
-4
PFD
avg
for T
1
= 5 years
8.08 x 10
-4
PFD
avg
for T
1
= 10 years
1.62 x 10
-3
PTC
100 %
Safety reaction time
Fault reaction time
3
< 20 ms
< 1000 ms
Table 3.1
1
The statement for the SIL rating is based on SFF, HFT and the assumption that this device typically uses 10 % of the failure budget
for the safety loop.
2
acc. to SN29500. This value includes failures which are not part of the safety function/MTTR = 24 h.
3
Time between fault detection and fault reaction
