Forum: Reliability & Maintainability Questions and Answers
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?
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?
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!!
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
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 0°C to ... but when temperature is for example -25°C ?
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