Endress+Hauser RN221N Handbuch Seite 13

RN221N
Management summary
This report summarizes the results of the hardware assessment carried out on the Active
Barrier preline RN 221N with hardware version as shown in the referred circuit diagrams (see
section 2.5.1).
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.
The failure rates used in this analysis are the basic failure rates from the Siemens standard
SN 29500. This failure rate database is specified in the safety requirements specification from
Endress+Hauser Wetzer GmbH + Co. KG for the Active Barrier preline RN 221N.
The listed failure rates are valid for operating stress conditions typical of an industrial field
environment similar to IEC 60654-1 class C (sheltered 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 Active Barrier preline RN 221N can be considered to be a Type A
hardware fault tolerance of 0.
It is assumed that the connected safety logic solver is configured as per the NAMUR NE43
signal ranges, i.e. the Active Barrier preline RN 221N with 4..20 mA current output
communicates detected faults by an alarm output current ” 3.6mA or • 21mA. Assuming that
the application program in the safety logic solver does not automatically trip on these failures,
these failures have been classified as dangerous detected failures. The following table shows
how the above stated requirements are fulfilled.
1
Type A element:
H[LGDFRP
©
Stephan Aschenbrenner
"Non-complex" element (all failure modes are well defined); for details see 7.4.4.1.2 of
IEC 61508-2.
GmbH
1
E+H Wetzer 13-03-087 R012 V2R1.doc, July 15, 2013
element with a
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