2
01
9-
07
14
Functional Safety HiD2872, HiC2873(Y1), HiD2876, HiC2877
Planning
SIL 2 Application (Bus Powered)
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
FMEDA report
Device type
A
Mode of operation
Low demand mode, high demand mode or continuous mode
Safety function
De-energized if the input is in low condition
HFT
0
SIL
2
SC
3
s
97 FIT
dd
0 FIT
du
30 FIT
total (safety function)
127 FIT
no effect
131 FIT
SFF
76 %
MTBF
1
1
acc. to SN29500. This value includes failures which are not part of the safety function/MTTR = 24 h.
The value is calculated for one safety function of the device.
293 years
PFH
2.96 x 10
-8
1/h
PFD
avg
for T
1
= 1 year
1.41 x 10
-4
PFD
avg
for T
1
= 2 years
2.70 x 10
-4
PFD
avg
for T
1
= 5 years
6.55 x 10
-4
PTC
99 %
Reaction time
2
2
Time between fault occurence and fault reaction
< 100 ms
Table 3.2