BERTHOLD TECHNOLOGIES Uni-Probe LB 490, User Manual

Page: 79 / 730

Uni-Probe LB 490
BERTHOLD TECHNOLOGIES GmbH & Co. KG
1 – 79
Volume 1 9 Functional Safety
1
©
exida.com
GmbH
berthold 0408-10 r003 v1r3.doc, Apr. 12, 2007
Rainer Faller
Page 13 of 18
5
Results of the assessment
ex
ida
did the FMEDAs together with Berthold Technology.
For the calculation of the Safe Failure Fraction (SFF) the following has to be noted:
O total
consists of the sum of all component failure rates. This means:
O total
=
O safe
+
O
dangerous
+
O no effect
+
O annunciation
O du total
=
O
du
+
O
annunciation undetected
SFF = 1 –
O
du total
/
O total
For
the
FMEDAs
failure
modes and distributions were used based on information gained from
[N3] to [N5]. 5.1
Level Transmitter LB490 Uni-Probe
The
FMEDA
carried out on the Level Transmitter LB490 Uni-Probe leads under the
assumptions described in section 4.2.3 to the following failure rates:
Failure category
Failure rates [FIT:=10
-9
/h]
Pre-amplifier, voltage divider and digital board
Fail Safe Detected
752
Fail Safe Undetected
97
Fail Dangerous Detected
261
Fail Dangerous Undetected
45
Annunciation
Detected
7
Annunciation
Undetected
5
No
Effect
313
Safe Failure Fraction
96,6%
4..20mA Output - new
Fail Safe Detected
31
Fail Safe Undetected
22
Fail Dangerous Detected
92
Fail Dangerous Undetected
1,3
Annunciation
Detected
43
Annunciation
Undetected
17
No
Effect
31
Safe Failure Fraction
92,3%
AC/DC-DC converter
Fail Safe Detected
0
Fail Safe Undetected
55
Fail Dangerous Detected
3
Fail Dangerous Undetected
0
Annunciation
Undetected
3
No
Effect
18
©
exida.com
GmbH
berthold 0408-10 r003 v1r3.doc, Apr. 12, 2007
Rainer Faller
Page 14 of 18
Failure category
Failure rates [FIT:=10
-9
/h]
Safe Failure Fraction
95,9%
Photomultiplier
Fail Dangerous Detected
21
Fail Dangerous Undetected
2,4
Safe Failure Fraction
90%
The
failure rates for the photo multiplier were evaluated from the field experience report of the
manufacturer Photonis. Remark: Due to the isolated mounting of the contacts in the Ex-D housing, the PG
inlet
and
the
O-ring to the connector room of the photo multiplier were not considered. Under
the
assumptions
described
in
section
4.2.3 the following table shows the failure rates
according to IEC 61508:
O
sd
O su
Total
=
O
su
+
O
no effect
O
dd
Total
=
O
dd
+
O ad
O
du
Total
=
O du
+
O
au
SFF DC
S
DC
D
783 fit
535 fit
427 fit
74 fit
96%
59%
85%
These failure rates are valid for operating stress conditions typical
of
an
industrial
field
environment similar to IEC 60654-1, class C (shel
tered
location)
with
an
average
temperature
over a long period of time of 40ºC (see chapter 4.2.3). For a higher average temperature
of
60°C,
the
failure
rates should be multiplied with an experience-based factor of 2.5. A similar
multiplier should be used if frequent temperature fluctuation must be assumed. Note that the “no effect” and “annunciation” failures on
its
own
will
not
affect
system
reliability
or
safety, and should not be included in spurious trip calculations. The PFD
AVG
was calculated for three different proof test intervals.
T[Proof] = 1 y
ear
T[Proof] = 2 y
ears
T[Proof] = 5 y
ears
PFD
AV
G
= 3,2E-04
PFD
AV
G
= 6,4E-04
PFD
AV
G
= 1,6E-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 35% of this range, i.e. to be better than or equal
to 3,5E-03.