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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:C.P. Chuah ( )
Organization:University of Sheffield
Date posted: Wed Nov 6 7:43:03 US/Eastern 2002
Subject: PRISM demo
I have downloaded the PRISM demo version. I am comparing between the predecessor and the example system for calculating failure rates. I however noticed that there is no difference between the predecessor system and the new system used by RACrates. Can someone tell me what's the difference. Thank you.


Subject: Purpose of predecessor system
Reply Posted by: David Dylis ( )
Organization: Reliability Analysis Center (RAC)
Date Posted: Mon Nov 11 11:32:06 US/Eastern 2002
In the real world, a "new" system or assembly is not necessarily a revolutionary advancement beyond the technology, processes, and complexities of a predecessor product. Rather, it may reflect an evolutionary improvement in performance that has only a marginal impact on the design or processes associated with its predecessor. For these situations, it is advantageous to factor in the field failure rate experience of the predecessor product to help predict the reliability of the "new" system or assembly.

The PRISM program accommodates this type of analysis through the use of its "Predecessor System/Assembly Analysis" function, available to the user from the relevant "Failure Rate" folder tab. The "Predecessor Analysis" function uses the PRISM-based reliability prediction of the predecessor product, and the observed field failure rate associated with that product, as a basis for estimating the reliability of the new system or assembly.

In order to use the Predecessor Analysis function of the program, there are 3 prerequisites that must be met:

1. The Predecessor system/assembly must have a PRISM-based reliability prediction performed on it (i.e., it must be defined within the PRISM System Manager).

2. The reliability prediction of the Predecessor must be fully summarized at the appropriate level, (i.e., system or assembly (a "Not Summarized" message must not be present on the "Failure Rate" folder tab of the Predecessor system/assembly)).

3. The Predecessor system must have observed failures and observed cumulative calendar hours available for it. Furthermore, each of the assemblies defined within that system must also have observed failures and cumulative calendar hours available for it. The "Observed Failures" and "Observed Cumulative Calendar Hours" are entered by the user using the Predecessor "Failure Rate" folder tab.

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