turck IM33-11-HI/24VDC - Page 30

Hans Turck GmbH & Co. KG • Tel. +49 208/4952-0 • Fax +49 208/4952-264
30
Safety Manual – Isolating Transducers
© exida.com GmbH TURCK 04-07-14 R001 V2R0.doc; February 8, 2013
Stephan Aschenbrenner Page 16 of 25
Fail-safe state = “fail high”
Failure Category
λ
λλ
λ
sd
λ
λλ
λ
su
λ
λλ
λ
dd
λ
λλ
λ
du
SFF DC
S
DC
D
λ
low
= λ
sd
λ
high
= λ
dd
233 FIT 315 FIT 73 FIT 44 FIT 93,40% 42,52% 62,39%
λ
low
= λ
dd
λ
high
= λ
sd
73 FIT 315 FIT 233 FIT 44 FIT 93,40% 18,81% 84,12%
Fail-safe state = “fail low”
Failure Category
λ
λλ
λ
sd
λ
λλ
λ
su
λ
λλ
λ
dd
λ
λλ
λ
du
SFF DC
S
DC
D
λ
low
= λ
sd
λ
high
= λ
dd
239 FIT 315 FIT 67 FIT 44 FIT 93,40% 43,14% 60,36%
λ
low
= λ
dd
λ
high
= λ
sd
67 FIT 315 FIT 239 FIT 44 FIT 93,40% 17,54% 84,45%
The PFD
AVG
was calculated for three different proof test times using the Markov model as
described in Figure 3.
T[Proof] = 1 year T[Proof] = 5 years T[Proof] = 10 years
PFD
AVG
= 1,92E-04 PFD
AVG
= 9,60E-04 PFD
AVG
= 1,92E-03
The boxes marked in yellow ( ) mean that the calculated PFD
AVG
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 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 ( ) mean that the calculated PFD
AVG
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
.
0,00E+00
5,00E-04
1,00E-03
1,50E-03
2,00E-03
2,50E-03
012345678910
P
r
o
b
a
b
i
l
i
t
y
Years
1oo1D structure
PFDavg
Figure 5: PFD
AVG
(t)