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Anhang
A.2 Prüfbericht (Auszug)
Management summary
This report summarizes the results of the hardware assessment with proven-in-use
consideration according to IEC 61508 / IEC 61511 carried out on the Electro-pneumatic
Positioner SIPART PS2 PA / FF. Table 1 gives an overview of the different configurations that
belong to the considered Electro-pneumatic Positioner SIPART PS2 PA / FF.
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. From the FMEDA, failure rates are determined and consequently the
Safe Failure Fraction (SFF) is calculated for the device. For full assessment purposes all
requirements of IEC 61508 must be considered.
Table 1: Configuration overview
[Conf 1] 6DR551*_*E***_****
[Conf 2] 6DR551*_*N***_****
[Conf 3] 6DR561*_*E***_****
[Conf 4] 6DR561*_*N***_****
For safety applications only the shut-down input (terminal 81/82) with the corresponding
pressure output was considered to work as a single-acting shut-down module ("tight closing").
All other possible input and output variants or electronics are not covered by this report.
The failure rates of the electronic components used in this analysis are the basic failure rates
from the Siemens standard SN 29500.
SIEMENS AG, A&D PI TQ2 and exida.com
mechanical parts of the Electro-pneumatic Positioner SIPART PS2 to calculate the mechanical
failure rates using different failure rate databases ([N6], [N7], [N8] and exida 's experienced-
based data compilation) for the different mechanical components (see [D17] and [R3]). The
results of the quantitative analysis are included in the calculations described in sections 5.2 and
5.3.
According to table 2 of IEC 61508-1 the average PFD for systems operating in low demand
mode has to be ≥10
PFD
that 50% of the total SIF PFD
pneumatic Positioner SIPART PS2 PA / FF is only one part of the final element it should not
claim more than 20% of the range. For a SIL 2 application the total PFD
should be smaller than 1,00E-02, hence the maximum allowable PFD
would then be 2,00E-03.
The Electro-pneumatic Positioner SIPART PS2 PA / FF when using the shut-down input
(terminal 81/82) for the safety function is considered to be a Type A
hardware fault tolerance of 0.
For Type A components the SFF has to be between 60% and 90% for SIL 2 (sub-) systems with
a hardware fault tolerance of 0 according to table 2 of IEC 61508-2.
1
Type A component:
©
exida.com
Stephan Aschenbrenner
A-4
PROFIBUS PA EEx; single-acting
PROFIBUS PA Standard; single-acting
FF EEx; single-acting
FF Standard; single-acting
-3
-2
to < 10
for SIL 2 safety functions. A generally accepted distribution of
values of a SIF over the sensor part, logic solver part, and final element part assumes
AVG
AVG
"Non-complex" component (all failure modes are well defined); for details see
7.4.3.1.2 of IEC 61508-2.
GmbH
together did a quantitative analysis of the
value is caused by the final element. However, as the Electro-
siemens 05-01-04 r014 v1 r1.0.doc, August 16, 2005
Ergänzungen zum Gerätehandbuch, 09/2005, A5E00489774-01
value of the SIF
AVG
value for the positioner
AVG
1
component with a
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