Functional Safety KCD2-RR2-Ex1(.SP)
Planning
20
19
-1
1
11
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
2
SC
3
Safety function
Transfer of the resistance values with
an accuracy of 2%.
s
1
0 FIT
dd
134 FIT
du
54.4 FIT
total (safety function)
1
188 FIT
not part
377 FIT
SFF
1
71.1 %
MTBF
2
164 years
PFH
5.44 x 10
-8
1/h
PFD
avg
for T
1
= 1 year
2.38 x 10
-4
PFD
avg
for T
1
= 2 years
4.77 x 10
-4
PFD
avg
for T
1
= 3 years
7.15 x 10
-4
PTC
100 %
Reaction time
3
< 20 ms
Table 3.1
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.
2
acc. to SN29500. This value includes failures which are not part of the safety function/MTTR = 8 h.
3
Time between fault detection and fault reaction
