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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: Andrew Comons
Date posted: Fri Mar 29 13:59:26 US/Eastern 2002
Subject: Exponential Conditional Reliability...A Paradox?
I recently came across a derivation of the "Exponential Conditional Reliability" equation which states that regardless of previous accumulated age, the reliability of a system is only dependent on the duration of the present mission, i.e., no "memory" of what occurred prior to the present mission. I fully understand the arithmetic of the derivation, but not the principle. According to the theory, I could momentarily shut a system down in the middle of a mission, turn it back on and expect the same probability of success as at the start of the initial mission. This does not seem practical or realistic, but the math says oterwise. Can anyone explain this paradox?? Thanks in advance

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Subject: Overstress is not a reliability failure
Reply Posted by: tom c
Date Posted: Wed Apr 3 13:33:13 US/Eastern 2002
I have recently become a believer that the exponential distribution is very likely the incorect model for most real complex electronic/mechanical systems. The idea of a constant failure probably isn't valid very often. If the type of overstess that Patrick refers to, one that exceeds the design limit of the device, causes failure - well this is not a reliability failure, but one that the equipment was never intended to withstand. An overstress condition can not be considered a relevant failure and would not be covered by any warranty.

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