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  #11  
Old November 2nd, 2010, 12:28 PM
David David is offline
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Default Re: How to use test data of subsystems

Thank you for the link. I understand that you have previously discussed this method with someone from our Theoretical group. We will certainly consider it and get back to you if we have any questions.
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  #12  
Old November 11th, 2010, 10:57 AM
Oleg_I Oleg_I is offline
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Default Re: How to use test data of subsystems

There is a continuation of this discussion at http://reliability-discussion.com/showthread.php?t=2394.

Last edited by Oleg_I; November 13th, 2010 at 07:47 AM.
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  #13  
Old November 18th, 2010, 09:14 AM
Oleg_I Oleg_I is offline
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Default Re: How to use test data of subsystems

It seems a case of the paradox "whole - parts".
If we estimate a reliability of each component separately and use the typical (r1*r2*r3) we derive a low reliability of a system.
But if we do not estimate a reliability of each component separately, how we do it for tests of the system we will get a higher estimation of reliability of a system.
Mathematically it can be defined as:
1. Testing of the n systems with three components

1-CL = (r1*r2*r3)^n => rs = (r1*r2*r3) = (1-CL)^(1/n)

2. Testing of all components separately (the n tests of each component):

1-CL = r1^n * r2^n * r3^n => rs = (r1*r2*r3) = (1-CL)^(1/n) - the expression remains the same

3. Testing of all components separately (the n1 tests of 1st component, n2 tests of 2nd component, n3 tests of 3rd component, n1>n3, n2>n3):

1-CL = r1^n1 * r2^n2 * r3^n3 => rs = (r1*r2*r3) = ((1-CL)/r1^(n1-n3)/r2^(n2-n3))^(1/n3) - rs depend on r1, r2 here.

Find rs->min (the worst case) therefore
r1=1
r2=1
rs = r3 = (1-CL)^(1/n3)

For example:
n1=50, n2=60, n3=27, CL=0.9
The method <http://www.reliasoft.com/pubs/2010_R...ot_systems.pdf> gives us
rs=0.874 (see attachment)
This method gives us
rs=(1-0.9)^(1/27)=0.918

What is correctly?
Attached Files
File Type: xls ApproxBeta.xls (14.5 KB, 9 views)

Last edited by Oleg_I; November 19th, 2010 at 05:37 AM.
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  #14  
Old April 3rd, 2017, 09:20 PM
Oleg_I Oleg_I is offline
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Default Re: How to use test data of subsystems

There is a continuation of this topic http://nomtbf.com/2016/04/lifetime-evaluation-vs-measurement-part-2/#more-1888
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