On 09/12/2016 07:04 AM, Scott Lurndal wrote:
T writes:
On 09/10/2016 12:41 PM, Ed Pawlowski wrote:
tolerance for MTBF
Hi Ed,
That is not what MBTF means. If the bulb had, say 1000 hour
MBTF, it would mean that you put 1000 bulbs in a test bench
and ran them for an hour. Only one failed. MBTF does not
tell you anything about the second and so forth hours.
(I did MBTF analysis for the military.)
Yet, you can't even spell the acronym correctly.
And "YOU" never make a typo? Oh pardon me!
MTBF - Mean Time Between Failures
"The predicted elapsed time betwen inherent failures of a system
during operation".
Oh no you misspelled "between"! Oh My Gosh!!!! A TYPO,
A TYPO, A TYPO !!! You must have gone to the same publik
skool I went to! AAAAAAHHHHHHHH !!!!!
You also gave a superficial definition. The full definition
is
Mean time between failures (MTBF). The total functioning
life of a population of an item divided by the total number
of failures within the population during the measurement
interval. The definition holds for time, cycles, miles,
events, or other measures of life units.
--DOD-HDBK-791, page 215
You missed the "measurement interval". It is one hour. I have
done this professionally for the military. There is much more to
it than the superficial definition you gave. And it does lead
to a lot of misunderstandings, like yours. The general public
does not realize the tables you use to look these things up (also
published by the miliary) are all based on one hour. You
are relying on the work of others to come up with your
predictions. Intervals other than an hour would require
all kinds of math manipulations to combine it with MTBF of other
parts analyzed in your prediction. You are not just analyzing
one part by itself, you can just look that up.
Note that it is incorrect to extrapolate MTBF to give an estimate
of the life time of a component, because of the much higher failure
rate during end-of-life.
It is improper to interpolate Mean Time To Failure (MTTF)
with with MTBF do to the way MTBF is calculated.
And, I do not mean to poke the condescending in the eye, but
infant Mortality and Old Age Failure (Wear Out Failure)
match each other (one is the inverse of the other). It
is called the Bathtub curve.
https://en.wikipedia.org/wiki/Bathtub_curve
Now you can go back happily condescending about all
our typos, not yours, of course.
And yes, I had to study all the above ****.