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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: Roberto Poli (design@gitronica.com )
Organization:Gitronica s.r.l.
Date posted: Tue May 18 6:35:32 US/Eastern 1999
Subject: Power on -off cycle failure rate
Message:
I'm using a software, based upon Mil-Hdbk 217 to evaluate MTTF of a domestic equipment. I need information about components failure rate during power on- off cycles. I have seen that Mil -Hdbk 217 doesn't consider power on-off stress parameters. Does this kind database exist? Any answer will be very appreciated. Thank you.


Reply:

Subject: Cycling Failure Conditions
Reply Posted by: Bruce Dudley (bdudley@alionscience.com )
Organization: Reliability Analysis Center
Date Posted: Tue May 18 10:56:36 US/Eastern 1999
Message:
Power cycling conditions in MIL-HDBK-217 only apply to relays as the data base used to form the failure models did not show or have information to relate to this on-off power condition. The Bellcore and CNET (French Telecom) models, also do not consider this condition for the general part population. The "NEW" RAC PRISM model, soon to be released, does have a cycling based failure rate (in addition to the operating and nonoperating failure rates)for the general population of part types (i.e. ICs, transistors, diodes, capacitors, resistors and thyristors). This factor is a function of the number of temperature cycles (cycling rate) over the life time of the part and the difference in temperature between dormant conditions and operating conditions (delta T). Therefore, based on these models, a user can perform tradeoff as a function of various operating, nonoperating and cycling conditions. The "NEW" RAC PRISM model is a software product that will predict system reliability values for numerous conditions and part types. It, also will integrate test information and software failure conditions into the prediction model. This new and advanced prediction model will be available in the early fall time frame. If you have an urgent need to solve the temperature cycling problem, please contact us directly.


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