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Forum: Reliability & Maintainability Questions and Answers

Topic: Reliability & Maintainability Questions and Answers

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

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Posted by: John
Date posted: Thu May 31 23:40:56 US/Eastern 2001
Subject: Field Data
When analyzing field data for specific part failures (like an electric motor)in a large population - Do you use time to first failure for unique units and then do Weibull plots? Do you ignore any follow up failures of this part in these units? The sample size would be several hundred units. I would like to use this information in determining base failure rates for future reliability predictions. Thank you


Subject: Field Data Analysis
Reply Posted by: Patrick Hetherington ( )
Date Posted: Fri Jun 1 7:15:38 US/Eastern 2001
It really depends on the purpose of the field data analysis. Using Weibull (or other distribution analysis such as normal, lognormal, exponential, etc) the items are being treated as a non-repairable item. Looking at the times to first failure is the only applicable method of Weibull analysis for your parts (i.e. electric motors). This will tell the failure pattern and thus failure distribution of the part as a whole (manufacturing defects, random, wear out). Remember to treat non-failed units as suspensions. This may not be enough information to determine how to improve the reliability of the part, but will provide information to the contribution or degradation to overall system reliability based the part. Separating the time to first failure by failure mode and doing a Weibull analysis on each data set will provide further insight to the greatest areas for improvement. If you were looking for trends in a repairable system, applying the Non-homogenous Poisson Process would be applicable. If you would like us to look at the data and make recommendations, please feel free to e-mail me directly.

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