2
01
9-
11
12
Functional Safety NCN3-F31K2(M)-N*-B*3-S
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
).
Parameter
Characteristic values
Assessment type and
documentation
Full assessment
Device type
A
Mode of operation
Low Demand Mode or High Demand Mode
HFT
0
Safety function
High impedance state, depending on the position of the measuring plate
SIL
2
in combination with a control unit according to EN 60947-5-6 (NAMUR)
SC
3
s
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.
107 FIT
du
66 FIT
total (safety function)
173 FIT
SFF
1
62 %
PFH
6.55 x 10
-8
1/h
PFD
avg
for T
1
= 1 year
2.87 x 10
-4
PFD
avg
for T
1
= 2 years
5.74 x 10
-4
PFD
avg
for T
1
= 5 years
1.43 x 10
-3
MTTF
d
1730 years
Useful life time
20 years
Reaction time
2
2
Step response time, also valid under fault conditions (including fault detection and fault reaction)
< 1 ms
Table 3.1
