KROHNE SU 501 EX EN - Manual (Page 30)

PFD
avg
T
Proof
= 1 year
T
Proof
= 5 years
T
Proof
= 10 years
<0.044x10 -2
<0.218x10 -2
<0.436x10 -2
PFH <0.1x10 -6 /h
Double channel architecture
If the measuring instrument is used in a double channel
architecture, the safety-relevant characteristics of the selected
structure of the measuring chain must be calculated acc. to the
above failure rates (especially for the selected application). A
Common Cause Factor must be taken into account which is in
the worst case 10 %.
The following is applicable:
SIL3 (Safety Integrity Level)
HFT = 1 (Hardware Fault Tolerance)
The time-dependent process of PFD
avg
reacts in the time
period up to 10 years virtually linear to the operating time. The
above values only apply to the T
Proof
interval, after which a
recurring function test must be carried out.
1 5 10
T
Proof
PFD
avg
1
2
3
4
Fig. 9: Time-dependent process of PFD
avg
2)
1 PFD
avg
= 0
2 PFD
avg
after 1 year
3 PFD
avg
after 5 years
4 PFD
avg
after 10 years
2) Numbers see in the above charts.
Architecture 1oo1D
Time-dependent process of
PFD
avg
30 SU 501 Ex - Signal conditioning instrument
Functional safety
27953
-EN
-050616