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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: Fred Levesque
Organization:Raytheon
Date posted: Fri Dec 1 9:31:16 US/Eastern 2000
Subject: Environmental Conversion Factors
Message:
I am looking at the RAC Reliability Toolkit: Commercial Practices Edition, page 176. I want to convert a system series MTBF from a particular temperature and environment to a different temperature and a different environment. Do I apply both the environmental conversion factor from the environmental table AND the temperature conversion factor from the temperature table? I was previously told to use ONLY the environmental factor, which does not seem reasonable.


Reply:

Subject: Reliability Toolkit Translation
Reply Posted by: Bruce Dudley (bdudley@alionscience.com )
Organization: Reliability Analysis Center
Date Posted: Mon Dec 4 13:58:55 US/Eastern 2000
Message:
The Reliability Toolkit: Commercial Practices Edition” has translation factors for “estimating” the relative impact of an equipment that has field or predicted data at one set of conditions and needs to be estimated at another set of conditions. The translation factors in the toolkit account for three different types of situations: quality change, temperature change, and environment change. Quality and temperature translations are single parameter considerations. The environmental translation accounts for more than one parameter. Specifically, it accounts for temperature change, vibration increase or decrease and humidity variation. Therefore, given that the translation applied is an environmental change, this means it already has the temperature impact and reapplying the temperature will result in a far more pessimistic translation. Since the tool is only an approximation, I always recommend that one should follow this approximation with real test data or by performing a detailed stress reliability analysis at the conditions specified. One should review these data to see if all components actually meet the operating and non-operating envelopes.


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