calculate MTBF
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From: JosephKK on 24 Jan 2010 20:25 On Fri, 22 Jan 2010 13:19:16 +0000, Raveninghorde <raveninghorde(a)invalid> wrote: >On Fri, 22 Jan 2010 02:02:42 -0800, Robert Baer ><robertbaer(a)localnet.com> wrote: > >>Raveninghorde wrote: >>> On Thu, 21 Jan 2010 10:24:29 -0500, Rich Webb >>> <bbew.ar(a)mapson.nozirev.ten> wrote: >>> >>>> On Thu, 21 Jan 2010 15:06:10 +0000, Raveninghorde >>>> <raveninghorde(a)invalid> wrote: >>>> >>>>> How do you calculate MTBF? >>>> For a component? For an entire system? 217 or Bellcore/Telcordia or .... >>>> >>>> The Wikipedia article isn't a bad place to start. If you're tasked with >>>> doing a full-up parts-stress reliability prediction analysis, good luck! >>> >>> For a lithium ion battery charger. >>> >>> My brief post was a cry of despair. I ship these by the hundred. Now a >>> BIG US company wants them and I get asked for a bucket load of >>> information. >>..as long as they PAY for the info and time to compile it. > >Nope. They would prefer the BOM and do the calculation themselves. >Since I won't give the BOM it's down to me sort it out. Basically it is the _statistical_ point where the root sum square failure rate of the individual components becomes 50% probability.
From: Rich Webb on 25 Jan 2010 08:24
On Sun, 24 Jan 2010 17:25:56 -0800, "JosephKK"<quiettechblue(a)yahoo.com> wrote: >On Fri, 22 Jan 2010 13:19:16 +0000, Raveninghorde <raveninghorde(a)invalid> wrote: > >>On Fri, 22 Jan 2010 02:02:42 -0800, Robert Baer >><robertbaer(a)localnet.com> wrote: >> >>>Raveninghorde wrote: >>>> On Thu, 21 Jan 2010 10:24:29 -0500, Rich Webb >>>> <bbew.ar(a)mapson.nozirev.ten> wrote: >>>> >>>>> On Thu, 21 Jan 2010 15:06:10 +0000, Raveninghorde >>>>> <raveninghorde(a)invalid> wrote: >>>>> >>>>>> How do you calculate MTBF? >>>>> For a component? For an entire system? 217 or Bellcore/Telcordia or ... >>>>> >>>>> The Wikipedia article isn't a bad place to start. If you're tasked with >>>>> doing a full-up parts-stress reliability prediction analysis, good luck! >>>> >>>> For a lithium ion battery charger. >>>> >>>> My brief post was a cry of despair. I ship these by the hundred. Now a >>>> BIG US company wants them and I get asked for a bucket load of >>>> information. >>>..as long as they PAY for the info and time to compile it. >> >>Nope. They would prefer the BOM and do the calculation themselves. >>Since I won't give the BOM it's down to me sort it out. > >Basically it is the _statistical_ point where the root sum square failure rate >of the individual components becomes 50% probability. Note that for the often used exponential distribution (applicable for a constant failure rate), we will then have the reliability at time t as R(t) = exp(-t/MTBF). So the probability that any one component actually survives to its MTBF is only about 37%. -- Rich Webb Norfolk, VA |