PRISM Forum - Message Replies


Topic: PRISM Questions and Answers
Topic Posted by: SRC (src_forum@alionscience.com )
Organization: SRC
Date Posted: Wed Jan 12 8:33:33 US/Eastern 2000
Topic Description: Welcome to the PRISM forum! Please feel free to post your questions and comments about the PRISM assessment software here.

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Original Message:

Posted by: Ralph Listl (ralph.listl.t-systems@eads.com )
Organization:EADS
Date posted: Mon Feb 27 5:36:41 US/Eastern 2006
Subject: Dormant Temperature
Message:
One of the environment factors that is used for calculation is the dormant temperature. If this value is changed (leaving all other parameters unchanged)is has influence on the overall reliability. Could you please give a detailed explanation (formula) where the dormant temperature influences the failure rate and how it is used within the model (what conditions/assumptions are used). Currently we are in a project where this temperature is not defined and we need an understanding which value we should choose for our calculation.


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Reply:

Subject: Temperature Dependency
Reply Posted by: Ralph List
Date Posted: Tue Mar 6 5:20:19 US/Eastern 2007
Message:
Thank you very much for your prompt response. I agree to your statement of having the temperature as a parameter that has influence on the inherent failure rate of an item as well as to the process of manufacturing of the item. Temperature has from my point of view no influence on the desgin and development process. The modell that is used by PRISM makes it possible to change the temperature in the environment area. if you do this and change for example the OP. temperature from 85C to 70 C, trickle down through the system, you receive a different failure rate for the system and a different proces grade factor. This is as far as I understand reliability predictions not correct. The OP. temperature is the temperature used during operation of the item and is used for calculation of the inherent failure rate. Within PRISM it is also used for the environmental factor in the process grade factor. This must not be mixed. For the process grade factor other temperature set! tings must be used. How is the temperature really used within PRISM during calculation of the environmental factor ? I hope this explanation makes it more clear, where I see the difficulties in the PRISM model.


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