BERTHOLD TECHNOLOGIES Uni-Probe LB 490, Руководство пользователя

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Uni-Probe LB 490
BERTHOLD TECHNOLOGIES GmbH & Co. KG
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Volume 1 9 Functional Safety
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Failure Modes, Effect
s and Diagnostics
Analysis
Project:
Level Transmitter LB490 Uni-Probe
Customer:
Berthold Technologies GmbH & Co. KG
Bad Wildbad
Germany
Contract No.: Berthold Technology 04
/
08-10
Report No.: Berthold
T
e
chnology 04/08-10 R003
V
ersion V1, Revision R3,
Apr
. 2007
Rainer Faller
©
exida.com
GmbH
berthold 0408-10 r003 v1r3.doc, Apr. 12, 2007
Rainer Faller
Page 2 of 18
Management summary
This report summarizes the results of the hardware assessment
according
to
IEC
61508
carried
out on the Level Transmitter LB490 Uni-Probe. For safety applications only level measurement and the 4..20mA output is considered. The HART™ communication shall
not
be
used
for
safety
applications. The configuration set up using HART™ shall be checked by functional testing. The
hardware
assessment consists of a Failure Modes, Effects and Diagnostics Analysis
(FMEDA).
A
FMEDA
is
one
of
the
steps taken to achieve functional safety assessment of a
device per IEC
61508. For full assessment purposes
all
requirements
of
IEC
61508
must
be
considered. From the FMEDA, failure rates are determined and consequently the Safe
Failure
Fraction
(SFF) is calculated for the device. A dangerous failure is defined as
a
failure
that
does
not
correctly
respond
to
a
demand
from the process outside a measurement band of more than 5%
full
span
at
ambient
temperature.
Failure
rates
used in this analysis are basic failure rates from
the
Siemens standard SN
29500. For the photo-multiplier field failure evaluations from Berthold
Technologies
and
the manufacturer (Photonis) were used. For the mechanical design of the
detector unit field failure evaluations from Berthold Technologies were used. The
Level
Transmitter
LB490
Uni-Probe is considered to be a Type B sub-system with a
hardware fault tolerance of HFT=0. It
is
assumed
that the current output signal is fed to a SIL compliant analog input of a safety
PLC (programmable logic controller). The analog input and
the
application
program
of
the
connected safety PLC shall be configured according to NAMUR NE43 to detect under-range and
over-range
failures.
Under
the assumptions described in section 4 the following table shows
the
failure rates according to IEC 61508. Additional to the FMEDA, fault injection tests have
been executed to confirm the effectiveness of the fault detection mechanisms.
Table 1 Summary
for the Lev
el Transmitter LB490 Uni-Probe incl. photomultiplier – IEC 61508
Failure rates
O
sd
O su
O
dd
O du
SFF DC
S
1
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.
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. The failure rates do not include failures resulting from incorrect use of
the
transmitter,
in
particular
high
vibration
at the photomultiplier tube and humidity entering through incompletely
closed housings or inadequate cable feeding through the PG inlets. A user of the Level Transmitter LB490 Uni-Probe can utilize these failure
rates
in
a
probabilistic
model of a safety instrumented function (SIF) to determine suitability in part
for
safety
instrumented
system
(SIS)
usage
in
a particular safety integrity level (SIL). A full table of failure
rates is presented in section 5.1 along with all assumptions in section 4.
1
DC means the diagnostic coverage (safe or dangerous).