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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: Alex Troya (troya@solarturbines.com )
Organization:Solar Turbines, Inc.
Date posted: Wed May 23 0:59:58 US/Eastern 2001
Subject: Improving MTBF
Message:
I am doing a reliability study for a standby generator control system. I learned that one way to reach the target MTBF is by increasing the testing frequency. The formula I found to calculate the testing factor is MTBF/2 * target MTBF. The results seem dubious - can you validate this formula? Thank you.


Reply:

Subject: Improving MTBF
Reply Posted by: Jim Smith (jamsmi@ballard.com )
Date Posted: Thu May 24 16:58:05 US/Eastern 2001
Message:
Increasing testing frequency will do absolutely nothing to improve MTBF. The only way to improve MTBF is to change the design. Increasing the testing frequency will improve the probability of finding the system operationally ready, when it is called upon to function. The formula that you were probably refering to is that Unreliability, while dormant, is (failure rate * time between tests)/2. This gives a time averaged probability of failure during the interval between tests. Thus if you increase the test frequency, you reduce the time between tests and reduce the unreliability. If you want a more detailed discussion, please e-mail me. Jim Smith


Reply:

Subject: Improving MTBF via Testing
Reply Posted by: Edward Sherwin (esherwin@alionscience.com )
Organization: RAC
Date Posted: Tue May 29 15:03:30 US/Eastern 2001
Message:
Mr. Troya, your MTBF can not be improved by periodic testing the system. Since your system is a standby system, periodic testing will increase the reliability of the system when called upon. Periodic testing will find failures that can be corrected thus enhancing the reliability of the system. Using this formula, you can set the reliability you desired and test to determine how offen testing should occur. R(t)= exp(-lambda x t).


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