Functional Safety HiC284*
Planning
20
20
-0
7
13
3.4
Characteristic Safety Values
The characteristic safety values like PFD, PFH, SFF, HFT and T
1
are taken from
the 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
2
SC
3
MTBF
1
(HiC2841)
1
acc. to SN29500. This value includes failures which are not part of the safety function/MTTR = 8 h.
322 years
MTBF
1
(HiC2842)
253 years
Safety function
inverse operation
normal operation
s
140 FIT
141 FIT
dd
0 FIT
0 FIT
du
28.5 FIT
25.3 FIT
total (safety function)
272 FIT
272 FIT
SFF
83 %
84 %
PFH
2.85 x 10
-8
1/h
2.53 x 10
-8
1/h
PFD
avg
for T
1
= 1 year
1.25 x 10
-4
1.11 x 10
-4
PFD
avg
for T
1
= 2 years
2.50 x 10
-4
2.22 x 10
-4
PFD
avg
for T
1
= 5 years
6.24 x 10
-4
5.54 x 10
-4
PTC
100 %
Table 3.1
