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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: Ernie ( )
Organization:Thermal-Flow Designs, Inc.
Date posted: Sat Sep 14 13:33:43 US/Eastern 2002
Subject: 2 Fans in parallel reliability
Hi- I have 2 fans operating in parallel. Both have a MTBF of 20000 hours. If I am operating both...(dont consider MTTR) would the total MTBF be 10000hrs. Thank you, Ernie

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Subject: Wear-Out Devices
Reply Posted by: Joe Dzekevich ( )Raytheon
Date Posted: Mon Sep 16 17:01:07 US/Eastern 2002
Ernie - what you did is correct IF the fan failure rate is exponential. However, fans are wear-out devices. Where did the 20,000 hours come from? Is it a L10 number? Since fans wear-out, two operating fans will wearout in the same amount of time - the failure rates don't add. For fans, you may end-up with two numbers: a MTBF for any electronic controls and a MTTF for wear-out items like bearings. Life is never simple. :^) Joe

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