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Forum: Reliability & Maintainability Questions and Answers

Topic: Reliability & Maintainability Questions and Answers

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

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Original Message:

Posted by: Ken
Date posted: Sat Aug 31 1:03:39 US/Eastern 2002
Subject: AMSAA model
Message:
If our test data fails the AMSAA model, what other model can we used for RDGT? Is it a good alternative to use the first principle of total test duration divided by the number of failures to assess the instantaneous reliability of the system under test? What's the difference between instantaneous relaibility and demonstrated reliability?


Reply:

Subject: AMSAA Model
Reply Posted by: B.W.Dudley (bdudley@alionscience.com )
Organization: RAC
Date Posted: Wed Sep 4 13:10:02 US/Eastern 2002
Message:
Test data cannot fail the AMSAA model. This model only indicates if the reliability is growing, standing still or has negative growth. Another model that can be considered is the use of the Duane model. This model is similar to the AMSAA model with some slight difference in the methods to calculate growth, instantaneous reliability and test lenght.Instantaneous reliability is calculated in the Duane model by dividing the cumulative value by one minus the growth rate. So, if we have positive growth, the instantaneous reliability will be higher or better than the cumulative reliability.


Reply:

Subject: AMSAA
Reply Posted by: Wayne
Date Posted: Thu Sep 5 9:20:51 US/Eastern 2002
Message:
i experience a problem when using the AMSAA model that is my Instantaneous MTBF is higher than my test duration. For e.g i test for a duration of 1000hrs with only 2 failures that occur in the very beginning of the test. Based on this set of data i use the AMSAA Model and the Instantaneous MTBF m(t) of about 1500, which is HIGHER than my test duration. Why is it so? I thought that MTBF cannot exceed the number of test hours. Can enlighten? Is the m(t) a accurate representation of the system at the end of RDGT?


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