Decommissioning and withdrawal from service
© exida.com GmbH TURCK 04-07-14 R001 V2R0.doc; February 8, 2013
Stephan Aschenbrenner Page 17 of 25
5.2 Analog Signal Transmitters IM35-**Ex-Hi/24VDC
The FMEDA carried out on the Analog Signal Transmitter IM35-22Ex-Hi/24VDC leads under
the assumptions described in section 4.2.3 and 5 to the following failure rates:
λ
sd
= 0,00E-00 1/h
λ
su
= 4,60E-09 1/h
λ
dd
= 0,00E-00 1/h
λ
du
= 4,09E-08 1/h
λ
high
= 6,18E-08 1/h
λ
low
= 2,53E-07 1/h
λ
no effect
= 3,25E-07 1/h
λ
total
= 6,85E-07 1/h
λ
not part
= 2,02E-08 1/h
MTBF = MTTF + MTTR = 1 / (λ
total
+ λ
not part
) + 8 h = 162 years
Under the assumptions described in section 5 and the definitions given in section 4.1 the
following tables show the failure rates according to IEC 61508:
λ
λλ
λ
safe
λ
λλ
λ
dangerous
SFF
583 FIT 103 FIT 85,01%
The PFD
AVG
was calculated for three different proof test times using the Markov model as
described in Figure 4.
T[Proof] = 1 year T[Proof] = 5 years T[Proof] = 10 years
PFD
AVG
= 4,50E-04 PFD
AVG
= 2,25E-03 PFD
AVG
= 4,48E-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 6 shows the time dependent curve of
PFD
AVG
.
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