Functional Safety KFD2-RSH-1.2E.L*(-Y1)
Planning
2
01
9-
12
13
3.4
Characteristic Safety Values
Parameters
Characteristic values
Assessment type and
documentation
Full assessment
Device type
A
Mode of operation
Low demand mode or high demand mode
Safety function
Output is energized (ETS, energized to safe)
without diagnosis
with diagnosis
HFT
0
SIL
3
SC
3
s
1
300 FIT
300 FIT
dd
0 FIT
2.81 FIT
du
2
3.47 FIT
0.65 FIT
total (safety function)
1
304 FIT
304 FIT
total
2052 FIT
2052 FIT
SFF
1
98.8 %
99.8 %
MTBF
3
56 years
56 years
DC
avg
4
0 %
81.2 %
PTC
81.2 %
81.2 %
PFH
3.47 x 10
-9
1/h
6.52 x 10
-10
1/h
PFD
avg
for T
1
= 1 year
5
4.1 x 10
-5
7.6 x 10
-6
PFD
avg
for T
1
= 2 years
4
5.3 x 10
-5
1.0 x 10
-5
PFD
avg
for T
1
= 3 years
4
6.6 x 10
-5
1.2 x 10
-5
T
1
max.
6
6.5 years
35.0 years
Reaction time
7
< 2 s
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
While the diagnostic function is signaling the dangerous failure of one relay, the other two redundant relays continue to provide
the safety function. Exceptions are common cause failures that disrupt all three relays. While the diagnostic function is signaling
the failure, the probability of a dangerous undetected failure for the remaining two relays is increasing to 11.4 FIT.
3
acc. to SN29500. This value includes failures which are not part of the safety function/MTTR = 8 h. The value is calculated
for one safety function of the device.
4
Enable the internal fault detection to achieve a diagnostic coverage of 81.2 %. See chapter 5.1.
5
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
.
6
assuming 10 % of the PFD
avg
budget in the safety loop, T
1
= T
service
7
Step response time, also valid under fault conditions (including fault detection and fault reaction)
