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| Re: How MDBF is Figured (was:Worst NYC subway car MDBF rating ) (432618) | |||
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Re: How MDBF is Figured (was:Worst NYC subway car MDBF rating ) |
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Posted by Jeff H. on Sat May 19 01:03:54 2007, in response to Re: How MDBF is Figured (was:Worst NYC subway car MDBF rating ), posted by J trainloco on Fri May 18 21:51:55 2007. The mean distance between failure is NOT calculated by keepinga distance between failure counter on each individual car, and then averaging the readings of those counters. It is, as TD described, the total car mileage for a fleet divided by the total number of chargeable failures. Statistics theory says it is OK to do this, but I think only if the PDF is gaussian, I don't remember, where's Baumann when you need him? MDBF alone doesn't predict availability at all. One could have a car class which has a very high MDBF, but also a very high MTTR, and thus has poor availability. Placing the cars into semi-permanent link sets multiplies the average MTTR. |
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