On 3 Dec 2014, at 17:25, Jon Elson wrote: > On 12/03/2014 07:40 AM, Marius Liebenberg wrote: >> Andy >> MTBF is obtained by testing a number of units over a period of time at >> accelerated environmental conditions. > MTBF CAN be evaluated this way, and it is a more truthful > way to do it, but it requires a LOT > of units and long testing on hi-rel systems. So, the DoD, > long ago, came up with this > crazy scheme to do it ALL on paper, with not a single actual > test needing to be performed.
BS EN 61709:2001 is all about the mathematical projection of the probability of failure, and the prediction of the theoretical MTBF on the basis of the calculation. It's the recommended Standard... > This was all worked out by the Defense Electronic Supply > Center back in the 1970's, > and I watched in total shock and amazement when the trade > mags described how this > all was to be done. DESC no longer exists, and I think this > whole debacle had something > to do with that. > > You look up in a book published by DESC what the reliability > of a specific resistor, transistor, > capacitor, etc. was, and then add up all of those parts and > put them into an equation > that gives you a total reliability. NO mechanical parts > need APPLY! Motors, fans, bearings, > disk drives, etc. are totally reliable! Also, all > connectors, switches, and wiring are > not prone to failure. Yeah; and as for those MTBF figures for small bearings... The last lot I used in my lathe fixed steady lasted for ages; except for the one which failed after 15 minutes.... ruining the job. It was small consolation to be told the 'thousands of hours to failure' was an average... > > The whole system is TOTAL BALONEY, but it is STILL used in > many industries, because > it makes such WONDERFUL numbers, even though anybody who > cares KNOWS it > is all FAKE! (DoD knows the whole methodology is bogus, and > has gone back to > more supportable methods of assessing reliability.) > > Sorry, rant mode off for now. > > Jon > > ------------------------------------------------------------------------------ > Download BIRT iHub F-Type - The Free Enterprise-Grade BIRT Server > from Actuate! Instantly Supercharge Your Business Reports and Dashboards > with Interactivity, Sharing, Native Excel Exports, App Integration & more > Get technology previously reserved for billion-dollar corporations, FREE > http://pubads.g.doubleclick.net/gampad/clk?id=164703151&iu=/4140/ostg.clktrk > _______________________________________________ > Emc-users mailing list > Emc-users@lists.sourceforge.net > https://lists.sourceforge.net/lists/listinfo/emc-users ------------------------------------------------------------------------------ Download BIRT iHub F-Type - The Free Enterprise-Grade BIRT Server from Actuate! Instantly Supercharge Your Business Reports and Dashboards with Interactivity, Sharing, Native Excel Exports, App Integration & more Get technology previously reserved for billion-dollar corporations, FREE http://pubads.g.doubleclick.net/gampad/clk?id=164703151&iu=/4140/ostg.clktrk _______________________________________________ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
