On 12/03/2014 07:38 AM, Marcus Bowman wrote: > http://www.proz.com/kudoz/german_to_english/business_commerce_general/1072093-mio.html > tells us it is Million hours. > > Interestingly, though, the term does not appear in BS EN 61709:2011 Electric > components - Reliability - Reference conditions for failure rates and stress > models for conversion. > > 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. > > This whole system of evaluating MTBF came from some stupid US Defense Department acquisition requirement that reliability of equipment be calculated by a VERY rigid and methodical approach. You use the highest temperature the equipment is rated to operate at, then the lifetime of every electrical component is computed based on temperature (including self-heating from power dissipation) and then the whole system reliability is computed with an equation that combines all the parts.
It totally screws up because it does not include connectors, wiring, solder joints, fan motors, drive motors, etc. So, that is why disk drives have these multi-100K hour MTBFs quoted. Everybody knows if you run a typical hard drive for 5 years you are deeply into living on "borrowed time". 5 years is 40K hours. So, the whole system si so TOTALLY flawed as to be absolutely meaningless for any real "system". Certainly, anything that has aluminum electrolytic caps used in a power supply has a lifetime in the 20 - 40K hours range, although this is at least extended by periods where the equipment is off, and made worse by high temperatures. One other place the military screwed up, is Tantalum capacitors. These have the bad characteristic that they can be VERY reliable if used CONSTANTLY. That means either on all the time, or used every few days. But, make something with tantalum caps, test it rigorously, and then put it in a supply depot for a couple years, and you will almost CERTAINLY find the caps short out and blow (as in fire and smoke) when you then put it into use. The military pretty much outlawed aluminum electrolytics. 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
