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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: John K ( )
Date posted: Thu Aug 1 11:25:44 US/Eastern 2002
Subject: Calculating Reliability Growth
When calculating MTBF: Is there a preferred method for determining how much additional test time is needed relative to the previous MTBF in order to do the next calculation? Example: Four units are under test (MTBF target = 300 hrs, each unit is repaired and returned to test), your first MTBF (cumulative) calculation indicated a MTBF of 100 hours. In order to do your next update (calculation) is there a recommended number of additional hours needed? More than 100 hours or some multiple of 100 hours? or is less OK? Keeping in mind management wants regular MTBF updates (weekly). How do you handle this? Any references or comments would be greatly appreciated.


Subject: Growth Test
Reply Posted by: B. Dudley ( )
Organization: RAC
Date Posted: Thu Aug 8 11:24:20 US/Eastern 2002
Tracking growth test data can be done at any interval of time, however the shorter the interval the less likely you are to see any change until a significant time has elapsed. I would suggest that you update every 200 hours which would be approximately every other day given the use of four test items. Two hundred hour test increments will show the growth or lack of growth very nicely.

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