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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: Bob Valerius (robert_m_valerius@md.northgrum.com )
Organization:Northrop-Grumman Oceanic Systems
Date posted: Tue May 9 13:17:46 US/Eastern 2000
Subject: One Shot Device Reliability
Message:
What kind of analysis is reasonable to ask a vendor to supply to support a Probability of Success Requirement (>0.99999) for a one shot device? Thanks in advance!


Reply:

Subject: One Shot Device Reliability Analysis
Reply Posted by: Jack Farrell (jfarrell@alionscience.com )
Organization: Reliability Analysis Center
Date Posted: Thu May 11 11:36:51 US/Eastern 2000
Message:
Given the high degree of reliability required for your device, >.99999, verification by test would require a very large sample size. A test of this magnitude would not be reasonable for obvious reasons. A more reasonable approach would be to calculate the failure rate for your device and then estimate its reliability for a given life cycle. Since your device is a one-shot I would expect the failure rate due to dormant environmental conditions to be significant. I would ask your vendor to develop failure rates for both dormant and operation modes. Using the reliability function R(t) = e^(-lt), where "l" is the device failure rate for a given period and "t" is the length of the time period, I would solve R(t) for both the dormant period and the operational period. Your device reliability would then be the product of the R(t-dormant)and R(t-operational). Please note that only the exponentially distributed failures occurring during the device’s useful life are considered. Failures due to design inadequacies, manufacturing problems, and wear out are not considered.


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