836-837 / 973
a CSA International company
FMEA of the (close/open)
Circuit type B
1oo1 EQUATIONS
Parameter name
Symbol
Equation / source
Close/Open with
diag
Proof Test Interval
T1
Given, for this example
2190
Mean Time To Repair
MTTR
Given, for this example
8
Type A/B
type A
Given, for this example
type b
Total failures:
l
From FMEA
9.42E-08
Safe diagnosed failures:
l
SD
From FMEA
2.04E-08
Safe undiagnosed failures:
l
SU
From FMEA
2.38E-08
Dangerous diagnosed failures:
l
DD
From FMEA
3.22E-08
Dangerous undiagnosed failures:
l
DU
or High demand mode, PFH per (hour)
1.77E-08
Safe no-effect failures
l
NE
From FMEA
1.26E-06
Diagnostic coverage:
DC
l
DD
/ (
l
DU
+
l
DD
)
64%
Safe Failure Fraction:
SFF (
l
SD
+
l
SU
+
l
DD
) /
l
81 %
Channel equivalent down time
t
CE
(l
DU
/
l
D
)(T/2 + MTTR) + (
l
DD
/
l
D
) MTTR
3.97E+02
PFD
AVG
(using 61508-6 equation)
PFD
AVG
(l
DU
+
l
DD
) t
CE
1.98E-05
PFD
AVG
(using simplified equation)
PFD
AVG
l
DU
(T / 2+MTTR) + (
l
DD
MTTR)
1.98E-05
PFD
AVG
(using IEC 61508-6,equation) PFD
AVG
1- e
-(
λdd+λdu) tce
1.98E-05
SIL capability (Low demand mode)
SIL 1