At 04:21 PM 11/18/2009, Alan Melia wrote...
Sorry Mike , unless, as someone else said, the figures are derived
from
field failures over at least a good porton of the expected like the
MTBF
tells you absolutely nothing!!
That is exactly what I meant by "the real-world statistical form" -
data gathered from in-service operation, not lab tests (or worse, a
purely mathematical combination of individual component MTBFs, like one
resistor contributes X, an IC of a certain type contributes Y, etc.).
But, things have to start from somewhere (e.g. a need to deploy spares
for a new product) so manufacturers will use shortcuts (lab testing,
etc.) for initial numbers, then refine based on experience. That
doesn't mean the shortcut methods are useless, only that they're less
accurate. Something is better than "nothing," and a simple device can
be expected to have a higher MTBF than a complex one (assuming similar
technologies, manufacturing processes, etc.). So I don't agree with
your "absolutely nothing" statement. Having an HP5071 doesn't make a
Timex worthless.
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