So they tested a batch of parts and projected out to the point where 63 percent will have failed using some assumed distribution of failure times. Not hard to get to 171 years using that methodology. It ignores the common case where there is a mode of failure that causes the failures to be clustered, but at least it gives you a decent idea of what to expect relative to other, similar parts. I'm sure they are not claiming their MTBF is less than a year. Just to recap, the test results would be used to estimate the parameters of the assumed failure distribution. From the resulting statistical model, you would be able to determine the point at which a given percentage would fail
I was dragged kicking and screaming through a semester of reliability/probability/statistics sometime back in the '80s. So it's been a while since I knew exactly what they would be doing. But that's the gist of it. On Wed, Dec 3, 2014 at 9:27 AM, andy pugh <bodge...@gmail.com> wrote: > On 3 December 2014 at 13:38, Marcus Bowman > <marcus.bow...@visible.eclipse.co.uk> wrote: > > > I don't believe 1500 Million hours. It is, in any case, a calculated > value (not that there's anything wrong with that). If the unit contains > large capacitors, 1500 hours is a much more realistic figure. Short; yes. > But realistic. > > 63 days? That doesn't seem _that_ much more plausible than 170,000 years. > > Given that (statistically) only 38% of parts would be expected to get > to the MTBF time it looks even worse. > > The background here is a 24V supply for a pulse clock. The clock has > been running since 1957 and still would be were it not that the master > clock was in a demolished building. I would like to think that the PSU > I choose would last for 10 years or more. (I plan to put a > hot-swappable replacement in the case too) > > -- > atp > If you can't fix it, you don't own it. > http://www.ifixit.com/Manifesto > > > ------------------------------------------------------------------------------ > 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
