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Forum: Reliability & Maintainability Questions and Answers

Topic: Reliability & Maintainability Questions and Answers

Topic Posted by: Reliability & Maintainability Forum ( )
Organization: System Reliability Center
Date Posted: Mon Aug 31 12:47:36 US/Eastern 1998

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Posted by: Juan C. Rodenas ( )
Date posted: Tue Oct 31 4:00:34 US/Eastern 2000
Subject: Relex vs PRISM
I am trying to adquire a reliability software for my company. I have notice of two different programs for this Prism and Relex(reliability package). The differences in prices are significant but I do not find big differences. Does somebody on the forum have experience in both of them of have identified any important differences? Thank you in advance.


Mary Priore Subject: PRISM
Reply Posted by: ( )
Organization: RAC
Date Posted: Tue Oct 31 11:05:32 US/Eastern 2000
Relex software currently incorporates the Bellcore and Mil-HDBK-217 models for reliability prediction. MIL-HDBK-217 was the original standard for reliability. It was designed to provide reliability math models for nearly every conceivable type of electronic device. In 1994, as a result of the US Military Specifications & Standards Reform initiative, the mission of the MIL-HDBK-217 preparing activity was re-directed, leaving Mil-HDBK-217 to become obsolete, with no viable replacement or updates. The Bellcore reliability prediction model was originally developed by AT&T Bell Labs and was based on equations from MIL-HDBK-217, modified to better represent what their telecommunications equipment was experiencing in the field. ( A frequent complaint of 217 was overly pessimistic predictions for commercial devices/applications)The main concepts, however, between MIL-HDBK-217 and Bellcore were very similar. RAC developed PRISM to overcome a number of inherent problems with existing methodologies. First, RAC's over 11 billion part hours of data indicate that one of the main underlying assumptions of the 217 model, namely, that components failures are the main contributor to system failure rate, is incorrect. RAC data shows non-component-realted failures such as design, manufacturing, software, etc. to be major contributors to actual electronic system failure rates. PRISM was developed based upon this data and incorporates all of the main contributors to system-level failures. Other distinguishing features of PRISM are: PRISM includes new, up-to-date RACRates component models. PRISM models are based upon environmental CONDITIONS as opposed to set environmental CATEGORIES, PRISM takes in to account duty cycle and non-operating failures, models reliability growth and includes a software reliability estimate. PRISM also allows the user to tailor the prediction based upon all available data including field data on a similar "predecessor"system, and component-level test data. You may wish to download the PRISM DEMO Software at

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