Pepperl+Fuchs KFD2-UT2 Series - Characteristic Safety Values

2019-10
12
Functional Safety KFD2-UT2-(Ex)*(-1)
Planning
3.4 Characteristic Safety Values
The following tables contains no SFF data, since this value has to be calculated
with consideration of the connected field device.
KFD2-UT2-(Ex)*
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 with proven-in-use assessment
1
Device type B
Mode of operation Low demand mode
Safety function Transfer of analog value
HFT 0 (acc. to IEC/EN 61511)
SIL 2
SC 2

s
0 FIT

dd
2
333 FIT

du
3
79.2 FIT

no effect
4
295 FIT

total (safety function)
706 FIT

no part
33.4 FIT
SFF 81 %
MTBF
5
154 years
PFD
avg
for T
1
= 1 year
6
8.33 x 10
-4
PFD
avg
for T
proof
= 2 years
6
1.14 x 10
-3
PFD
avg
for T
proof
= 5 years
6
2.08 x 10
-3
PTC 90 %
Reaction time
7
• for temperature input: < 1.5 s
• for potentiometer input: < 3 s
Table 3.1
1
For the proven-in-use demonstration, sales figures, customer returns and questionnaires filled out by customers were used
which show that no unknown systematic faults are expected. The device is based on a former device that was evaluated
for a proven-in-use statement by exida.com GmbH.
2
"Fail high" and "Fail low" failures are considered as dangerous detected failures 
dd
.
3
"Annunciation failures" that only influence the diagnostic function were marginal and added to the 
du
.
4
"No effect failures" are not influencing the safety function and are therefore added to the 
s
.
5
acc. to SN29500. This value includes failures which are not part of the safety function/MTTR = 8 h.
6
Since the current PTC value is < 100 % and therefore the probability of failure will increase, calculate the PFD value
according to the following formula:
PFD
avg
= (
du
/ 2) x (PTC x T
1
+ (1 – PTC) x T
service
)
A service time T
service
of 10 years was assumed for the calculation of PFD
avg
.
7
Step response time