Forum: Reliability & Maintainability Questions and Answers

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Posted by: Vincent (limpl@ceo.st.com.sg )
Organization:CEO
Date posted: Mon Sep 16 23:24:12 US/Eastern 2002
Subject: Field MTBF
Message:
Currently, I am collecting field failures for my computation of Field MTBF. The fomular used : (Total fleet * utilization hours)/ total field failure.
Can someone advice is my compution on Field MTBF is correct if not what is the correct approach? As years passed more failures encountered. How many years of data must I collect in order reflect correct field MTBF? rgds

Replies:
Field MTBF
Jean-Marie CLOAREC Mon Sep 23 9:06:56 US/Eastern 2002

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Posted by: Wayne
Date posted: Mon Sep 16 7:25:00 US/Eastern 2002
Subject: AMSAA-unbiased beta
Message:
I read Mil-Std 189 on growth testing and come across the formula for calculating unbiased beta for small sample size. I assume they are refering to small sample size of failures. It is not stated how small the sample size is then i can use the unbiased beta?

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Posted by: Ernie (erniethurlow@yahoo.com )
Organization:Thermal-Flow Designs, Inc.
Date posted: Sat Sep 14 13:33:43 US/Eastern 2002
Subject: 2 Fans in parallel reliability
Message:
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

Replies: (list all replies)
2 fans
Jean-Marie CLOAREC Mon Sep 16 5:31:47 US/Eastern 2002
Wear-Out Devices
Joe Dzekevich Mon Sep 16 17:01:07 US/Eastern 2002
2 fans
Jean-Marie CLOAREC Fri Sep 20 5:29:31 US/Eastern 2002

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Posted by: Gary
Date posted: Tue Sep 10 16:27:57 US/Eastern 2002
Subject: Conversion from kilometers to hours
Message:
Is there a standard method for converting failures per million miles to failures per million hours in order to integrate a known value (i.e MMBF = 1500 miles) into a system level prediction (MTBF)?
Thanks!!

Replies: (list all replies)
Conversion Factor
BWD Wed Sep 11 13:50:13 US/Eastern 2002
Converting MTBF units
Larry George Fri Sep 13 17:33:39 US/Eastern 2002

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Posted by: George (gpyryt@draper.com )
Organization:Draper Laboratory
Date posted: Mon Sep 9 13:21:17 US/Eastern 2002
Subject: Estimating defect density for ESS
Message:
I'd like to use MIL-HDBK-344 procedures to:
1) Estimate an equipment's defect density. I have extracted data from the reliability prediction to estimate the defect density but I am struggling with the final result because I can't make sense out of the examples in the handbook. In the MIL-HDBK-344A example on page 5-14, the part quantities of section 9 do not add up to the total # of parts in section 11. Perhaps this is why I can't determine how they arrived at the numbers in sections 2, 3 and 4. In the Litton Systems/Rome Lab document ADA245735, I tried to use the data in Figure 2.8 to arrive at the 2.95 value in Table 2.1 for the ML environment, but again I was unsuccessful. Any helpful suggestions or references that can help with the estimation of defect density would be much appreciated.

Replies:
ESS
B.W.Dudley Tue Sep 10 14:07:20 US/Eastern 2002

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