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: Fred Levesque
Organization:Raytheon
Date posted: Mon Oct 23 14:28:00 US/Eastern 2000
Subject: 100% duty cycles
Message:
I was trying to simulate an operational failure rate (rather than calendar) by choosing a 100% duty cycle and zero cycling rate in the PRISM operating profile menu. I was dismayed, however, when I found that changing the dormant temperature caused the failure rate to change by a large amount. If you have a 100% duty cycle and zero cycles per year, how can the failure rate be a function of the dormant temperature entry?


Reply:

Subject: PRISM Dormant/Operational Temperature
Reply Posted by: David Dylis (ddylis@alionscience.com )
Organization: Reliability Analysis Center (RAC)
Date Posted: Wed Oct 25 11:22:17 US/Eastern 2000
Message:
You approach to calculate an operational failure rate is correct, however choosing a 100% duty cycle and zero cycling rate in the PRISM does not remove the affect of temperature cycling from the use environment. PRISM is using the lower temperature (Dormant, although in this case it is not actually dormant) and the upper temperature(operating) to account for temperature extremes in the environment for which you are performing the analysis. Therefore as you mention the failure rate will change when the temperatures within the expected environment are modified.


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