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Forum: Reliability & Maintainability Questions and Answers

Topic: Reliability & Maintainability Questions and Answers

Topic Posted by: Reliability & Maintainability Forum (src_forum@alionscience.com )
Organization: System Reliability Center
Date Posted: Mon Aug 31 12:47:36 US/Eastern 1998

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Original Message:

Posted by: Ten Lin Mei (tlinmei@dso.org.sg )
Organization:DSO National Laboratories
Date posted: Wed Jan 26 23:54:28 US/Eastern 2000
Subject: FMECA from Card/Module Level
Message:
I wish to reduce the time in performing FMECA and TA for a large system by starting the FMECA from card and module levels (instead of component level). However, if I adopt this method, inaccuracies will come in when estimating the failure mode apportionments. I can estimate the failure mode apportionment by tracing back the component failure modes that cause the particular card/module failure mode. But this may end up consuming equally long or longer time than the component approach. Is there any reference or standard library on typical card/module failure modes and failure mode apportionment rates ? Or is there any recommendation on a good estimation method ? Also, is there any suggestion on how to verify or validate that this card/module level approach has not lost out a lot in the accuracies compared to the component level approach ? By the way, how do people estimate failure mode apportionments in the functional approach of FMECA ? Tracing back the components that are failure causes ? Thank you.


Reply:

Subject: Functional Failure Mode Analysis
Reply Posted by: Bruce Dudley (bdudley@alionscience.com )
Organization: Reliability Analysis Center
Date Posted: Thu Jan 27 15:10:21 US/Eastern 2000
Message:
Failure Mode and Effects Analyses at the functional level are difficult to perform accurately as the underlying assumption is component details are "NOT" available. The purpose of the functional approach is to perform an early assessment of the design block diagram concept at a high level. From this analysis, decisions on redundancy, fail soft or improved reliability for areas of concern can be determined on a block by block basis. The usual failure modes that are considered at this level are input and output conditions such as no-output or degraded output with gross estimates of the failure rates and apportionment levels. I do not believe that a standard library of failure mode for module or card exist as do the modes for individual parts. When part details are available, the accuracy of the functional approach can be improved by investigating each part failure modes that effect the outputs and by revising the functional failure mode rates and apportionment. Generally, circuit cards and modules are considered a Functional Analysis.


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