Forum: Reliability & Maintainability Questions and Answers

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Posted by: Rob Poltz (getreliability@designanalytx.com )
Organization:Design Analytx International
Date posted: Tue Nov 5 12:37:02 US/Eastern 2002
Subject: FIT definition and derivation
Message:
There seems to be a misuse or misunderstanding of the term FITs and I was wondering its correct definition and derivation.
I believe the proper definition is "Failure Units" and the Acronym "FIT" is based on the Mnemonic for Failure Unit, not Failures in Time, as a growing number of people have come to believe is correct. An explanation of FIT derivation is that it was originally construed the same way the term "Bit" was derived by taking certain letters (B from Binary, and last two letters from the word "digit"), to form "Bit", and this explanation appears in several documents dating back to the early 80s. The same powers of ten apply,i.e., (10e9) or billion units. Since "time" is not the only unit of measure when calculating failure (hazard) rates, it seems ludicrous to perpetrate a misnomer definition or at least standardize its correct usage. I realize that MH217 document was based on 10e6 hrs. for electronics systems, but mechanical systems are more apt to be calculated in number cycles, rotations, events, or some other operations. What do you think?

Replies:
FIT definition
Chiew Peng Chuah Wed Nov 6 7:25:08 US/Eastern 2002

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Posted by: Andrew Rowland (darowland@aep.com )
Date posted: Mon Nov 4 11:20:38 US/Eastern 2002
Subject: Weibull Analysis Results
Message:
I am analyzing field failure data of an electronic system. When performing a Weibull analysis, I find a beta of 0.952 with 19 samples. The source of information is only accurate to the day (i.e., I only know what date a failure occurred, not exact time), so I expected some error from this. Given the age of the equipment being analyzed, it would be expected to be operating within it's useful life. How far from 1.00 does the beta need to be before I would be wrong in using an exponential distribution? How much error can I expect due to the time reporting limitations of my data source?

Replies: (list all replies)
Weibull Analysis
Jorge Romeu Tue Nov 5 15:39:54 US/Eastern 2002
Weibull Beta Confidence
Joe Dzekevich Tue Nov 5 16:45:14 US/Eastern 2002

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Posted by: Laewon Kim (laewonee@rotem.co.kr )
Organization:ROTEM company
Date posted: Tue Oct 29 23:17:08 US/Eastern 2002
Subject: Maintenance Man-hours
Message:
hi!
I want to get standards or reference which have data about elasped man-hours or time for each maintenance task implementation. Here maintenance tasks refer to visual inspection, replenishment/replacement of consumable parts, condition check, function test with power on, and etc. Those about railway rolling stock will be better. Thank you!!

Replies:
Maintainability Standard Times
bwd Wed Oct 30 15:14:14 US/Eastern 2002

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Posted by: Laurence (laurence1999@163.com )
Date posted: Tue Oct 29 10:18:57 US/Eastern 2002
Subject: maintainability demonstration
Message:
Who can help me?
I wonder if someone could give me some summrized message of maintainability demonstration. Please contact me: laurence1999@163.com

Replies:
Maintainability Demonstration
Joe Dzekevich Tue Oct 29 12:40:03 US/Eastern 2002

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Posted by: Jean-Marie CLOAREC (jean-marie.cloarec@ligeron.com )
Organization:LIGERON S.A.
Date posted: Fri Oct 25 10:11:26 US/Eastern 2002
Subject: Negative temperature
Message:
How calculate failure rate when ambiant temperature is negative. MIL HDBK 217 + RDF + ... are based on temperature from 0C to ... but when temperature is for example -25C ?

Replies: (list all replies)
Negative Temps
Joe Dzekevich Tue Oct 29 12:52:09 US/Eastern 2002
Negative temperature
Jean-Marie Cloarec Wed Oct 30 12:02:30 US/Eastern 2002

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