FMEDA â Accurate Product Failure Metrics - Exida

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The result of this change is that the total failure rate reported by the FMEDArepresents the total failure rate for all the components even if some of thosefailure rates do not lead to an observable failure at the product level. Observedfailure rates at the product level are predicted by the total failure rate minus theno effect failure rate because the no effect failures would, in most cases, only bediscovered by full parametric testing of the individual components.Functional Failure Mode AnalysisAlso in the early 2000’s functional failure mode analysis was added to theFMEDA process. In early FMEDA work, component failure modes were mappeddirectly to “safe” or “dangerous” categories per IEC 61508. This was relativelyeasy since everything that was not “dangerous” was “safe.” With multiple failuremode categories now existing, direct assignment became more difficult. Inaddition, it became clear that the category assignment might change if a productwere used in different applications. With direct failure mode category assignmentduring the FMEDA, a new FMEDA was required for each new application or eachvariation in usage.Under the functional failure mode approach, the actual functional failure modesof the product are identified. During the detailed FMEDA, each component failuremode is mapped to a functional failure mode. The functional failure modes arethen categorized according to product failure mode in a particular application.This eliminates the need for more detailed work when a new application isconsidered.Mechanical FMEDA TechniquesIt became clear in the early 2000’s that many products being used in safetycritical applications had mechanical components. An FMEDA done withoutconsidering these mechanical components was incomplete and potentiallymisleading. The fundamental problem in using the FMEDA technique was thelack of a mechanical component database that included part failure rates andfailure mode distributions.Using a number of published reference sources, exida began development of amechanical component database in 2003 [Gob03]. After a few years of researchand refinement [GOB07], the database has been published [exi06]. This hasallowed the FMEDA to be used on combination electrical / mechanicalcomponents and purely mechanical components.The FutureThis paper explains how FMEDA techniques have evolved over the past decadesince the first efforts to define the process were made. One result of this is thatFMEDA Development Paper, Revision 1.1 February 19, 2007 Page 6 of 8
older FMEDA reports (2002 and before) should not be used and should never becompared to newer work.It is clear that further refinement of the component database with selectivecalibration to different operation profiles is needed. In addition, comparisons ofFMEDA results with field failure studies have shown that human factors,especially maintenance procedures, have an impact on the failure rates andfailure modes of products. As more data becomes available, these factors canalso be added to FMEDA analysis.References[Col84] Collett, R. E. and Bachant, P. W., “Integration of BIT Effectiveness withFMECA,” 1984 Proceedings of the Annual Reliability and MaintainabiltiySymposium, NY: New York, IEEE, 1984.[AME87] H.A. Amer,and E. J. McCluskey, “Weighted Coverage in Fault-TolerantSystems,” 1987 Proceedings of the Annual Reliability and MaintainabiltiySymposium, NY: NY, IEEE, 1987.[GOB92] Goble, W.M., Evaluating Control Systems Reliability, Techniques andApplications, NC: Research Triangle Park, Instrument Society of America, 1992.[MOR94] FMEDA Analysis of CDM (Critical Discrete Module) – QUADLOG,Moore Products Co., PA: Spring House, 1994.[GOB98a] Goble, W.M., The Use and Development of Quantitative Reliability andSafety Analysis in New Product Design, University Press, Eindhoven Universityof Technology, Netherlands: Eindhoven, 1998.[GOB98b] Goble, W.M., Control Systems Safety Evaluation and Reliability,second edition, NC: Research Triangle Park: ISA, 1998.[GOB99] W. M. Goble and A. C. Brombacher, “Using a Failure Modes, Effectsand Diagnostic Analysis (FMEDA) to Measure Diagnostic Coverage inProgrammable Electronic Systems,” Reliability Engineering and System Safety,Vol. 66, No. 2, November 1999.[GOB03] W. M. Goble, “Accurate Failure Metrics for Mechanical Instruments,”Proceedings of IEC 61508 Conference, Germany: Augsberg, RWTUV, January2003.[EXi06] Electrical & Mechanical Component Reliability Handbook, exida, PA:Sellersville, 2006. See www.exida.com[GOB07] W.M. Goble and J.V. Bukowski, “Development of a MechanicalComponent Failure Database,” 2007 Proceedings of the Annual Reliability andMaintainabiltiy Symposium, NY: NY, IEEE, 2007.FMEDA Development Paper, Revision 1.1 February 19, 2007 Page 7 of 8
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