PRISM Forum - Message Replies

Topic: PRISM Questions and Answers
Topic Posted by: SRC ( )
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: Leroy Meyers ( )
Organization:DRS Communications
Date posted: Tue Nov 13 15:24:50 US/Eastern 2001
Subject: Making Sense of Prism
I just completed my first Prism reliability prediction. I used the same piece of equipment for which I used MIL-HDBK-217F previously. I was very interested in comparing the results, so I used a 100% duty cycle in Prism so that calendar hours would equal operating hours. Using 217, the failure rate of the equipment is 83 failures per million hours. I inserted all the same parts into Prism, and came up with a failure rate of 6. I'm thinking that 6 is a very low number; will anyone believe it? But then I realized that I forgot to put the software failure rate into Prism. That's understandable, because software is something that I never considered in a prediction before. So I entered in the software parameters. That alone gave me a failure rate of 17,071!! Now I'm at the other extreme - this failure rate is way too high, I can't use this! Has anyone else gone through this? How can I make sense of this? If you want to know the details of what I entered into Prism, you can contact me directly at

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Subject: predicting failure frequency
Reply Posted by: don miller ( )
Date Posted: Sat Jan 5 21:39:47 US/Eastern 2002

see the first posting by d. miller. The first thing to do each morning before work is to tell yourself that predicting failure frequency is meaningless.  All of the MHB 217----- is an expensive joke. all engineering activity related the the prediction effort should forever be eliminated from industry.

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