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Fail-safe state = "fail high"
Failure Category
λ
= λ
low
sd
λ
= λ
high
dd
λ
= λ
low
dd
λ
= λ
high
sd
Fail-safe state = "fail low"
Failure Category
= λ
λ
low
sd
λ
= λ
high
dd
λ
= λ
low
dd
λ
= λ
high
sd
The PFD
was calculated for three different proof test times using the Markov model as
AVG
described in Figure 3.
T[Proof] = 1 year
PFD
AVG
The boxes marked in yellow (
allowed range for SIL 2 according to table 2 of IEC 61508-1 and table 3.1 of ANSI/ISA–84.01–
1996 but do not fulfill the requirement to not claim more than 10% of this range, i.e. to be better
than or equal to 1,00E-03. The boxes marked in green (
values are within the allowed range for SIL 2 according to table 2 of IEC 61508-1 and table 3.1
of ANSI/ISA–84.01–1996 and do fulfill the requirement to not claim more than 10% of this
range, i.e. to be better than or equal to 1,00E-03. Figure 5 shows the time dependent curve of
PFD
.
AVG
y
i t
2,50E-03
i l
b
a
2,00E-03
b
r o
P
1,50E-03
1,00E-03
5,00E-04
0,00E+00
Figure 5: PFD
AVG
exida.com
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GmbH
Stephan Aschenbrenner
30
λ λ λ λ
λ λ λ λ
sd
su
233 FIT
315 FIT
73 FIT
315 FIT
λ λ λ λ
λ λ λ λ
sd
su
239 FIT
315 FIT
67 FIT
315 FIT
= 1,92E-04
) mean that the calculated PFD
1oo1D structure
0
1
2
3
4
(t)
λ λ λ λ
λ λ λ λ
dd
du
73 FIT
44 FIT
233 FIT
44 FIT
λ λ λ λ
λ λ λ λ
dd
du
67 FIT
44 FIT
239 FIT
44 FIT
T[Proof] = 5 years
PFD
= 9,60E-04
AVG
) mean that the calculated PFD
5
6
7
8
9
10
Years
PFDavg
TURCK 04-07-14 R001 V2R0.doc; February 8, 2013
Hans Turck GmbH & Co. KG • Tel. +49 208/4952-0 • Fax +49 208/4952-264
SFF
DC
S
93,40%
42,52%
62,39%
93,40%
18,81%
84,12%
SFF
DC
S
93,40%
43,14%
60,36%
93,40%
17,54%
84,45%
T[Proof] = 10 years
PFD
= 1,92E-03
AVG
values are within the
AVG
Page 16 of 25
DC
D
DC
D
AVG
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