On 11.04.13 08:06, Rohan McLeod wrote: > Erik Christiansen wrote: > > On 10.04.13 04:48, James Harper wrote: > >> The MTBF for the disk is given as 1000000 hours, while most other > >> ...........snip > > There are not many hours in a year, so 3 years is little compared to > > 10^6 hours. (That 114 year MTBF is quite impressive.) It does though > > halve for each 10°C rise above the temperature at which the lifetime is > > predicted. > > Would the converse hold true ie. doubling for each 10°C fall bellow the > temperature at which the lifetime is predicted?
Yes, if the equipment is rated to operate at those temperatures. The examples I gave are simply based on Arrhenius' law, which has long served for describing the failure rate of electronics, in addition to its use in chemistry. It's only an approximation, as mentioned here: http://www.osti.gov/bridge/purl.cover.jsp?purl=/841248-BSrmuy/webviewable/841248.pdf The last time I used the equation was when doing qualifying testing for the LED clock in the XD Falcon. We ran about two dozen clocks at 80°C for a couple of months, then jacked it up to 100°C for some more months. I don't expect that it holds for the mechanical parts of the disk drive. The point I was making was that the hot cupboard housing the drive would reduce the equipment's lifetime in a significantly non-linear way, out of proportion to temperature rise. How low you can reduce the temperature, in expectation of a lifetime doubling, depends on the operating range of the equipment. Wet electrolytic capacitors would quickly set a limit, and commercial grade semiconductor chips are only rated 0°-70°C, industrial -40°C to 85°C, and military -55°C to 125°C. In the case of the hard drive, the mechanicals and their lubrication would probably give up first. > and > > "Running at 80°C above nominal for 6 months is equivalent to > 128 years of life.)" would imply the test was conducted at 0°C; > is this standard or just for example? OK, with only commercial or industrial grade devices in the equipment, 80°C above nominal would be out of spec, since nominal is usually 25°C. It was just an example, showing how a century-long MTBF could be extrapolated from less than a year of testing, if device ratings permit. Erik -- I really didn't foresee the Internet. But then, neither did the computer industry. Not that that tells us very much, of course - the computer industry didn't even foresee that the century was going to end. - Douglas Adams _______________________________________________ luv-main mailing list [email protected] http://lists.luv.asn.au/listinfo/luv-main
