It's been a while since I designed aerospace hardware, but seems I remember we had both a calculated AND a demonstrated MTBF.
Back then we called it Mil-Std 781. (I am sure it morphed into more modern tests). We had both a pre-production qual-test and a production acceptance-test, both required to meet MTBF's, that were run for reliability. I took stock in them; as did others. They did have merit in predicting weak engineering designs catching weak designs during 'life' production. It wasn't 'simplistic' at all. Maybe the military and aerospace world is different from the 'commercial' world. -Don ============================================================== On Mon, 28 Mar 2016 13:04:23 +0200 Florian Teply <[email protected]> wrote: > Am Mon, 28 Mar 2016 01:32:03 +0200 > schrieb Attila Kinali <[email protected]>: > > > Yes, the MTBF is a very simplicistic measure and there are a couple > > of assumptions in its calculation which do not hold generally (or > > rather, it's rather seldom that they hold). Yet it gives a number to > > something that is otherwise relatively hard to measure and the number, > > even though flawed, makes it possible to compare different devices > > on their reliability. As this is more a rule of thumb comparison, > > you shouldn't read too much into a 10% difference. Yet a 100% > > difference is significant, no matter which of the assumptions do not > > hold. > > > Umm, well, even a 100% difference still might mean nothing if the > derivation of MTBF between different devices is based on different > assumptions. That both these derivations might be seriously flawed does > not help at all. > Yet, even MIL-Spec parts documentation does rarely contain sufficient > detail to assess the validity of the numbers in a certain application. > > At the very least, one would need to know acceleration factors for the > different failure mechanisms, and shape parameters of the > failure-vs-time plot. This kind of data I wouldn't expect to find > outside the manufacturers premises, and even there it's not likely to > be accessible if it exists at all. > > Best regards, > Florian > _______________________________________________ > time-nuts mailing list -- [email protected] > To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > and follow the instructions there. -- dlewis6767 <[email protected]> _______________________________________________ time-nuts mailing list -- [email protected] To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
