Its true they wont test a new product for 5 or 10 years to get an mtbf numb
er before selling it. In the case of an led or ssd drive, its not the firs
t one ever made. Manufacturers understand the devices, the physics, the fa
ilure modes, and have similar devices that have undergone testing for tens
of thousands of hours. That data allows estimates for the next similar dev
Yet, you can't even spell the acronym correctly.
MTBF - Mean Time Between Failures
"The predicted elapsed time betwen inherent failures of a system
Of course, in a system that can't be repaired, such as an LED
A19 bulb, the proper acronym is MTTF (Mean Time To Failure).
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.
Note also the first term is 'Mean', which implies failures on
either side of the computed MTBF can be expected.
Actually the highest failure rate per unit time is when the product
is new. "infant mortality" is a bigger issue than "old age".
I guess technically you are mabee correct, because just before they
fail - at whatever age, they are "approachiung end-of-life"
Predicting "end of life" becomes the issue. We had all kinds of
trouble with LED MR16 or GU10 (whichever the 12 volt ones are) so we
went back to halogens - these are in a 14-20 foot mceiling. They have
been in a month now, and already 3 out of 54? are dead.......
On Monday, September 12, 2016 at 12:55:37 PM UTC-4, firstname.lastname@example.org wrote:
If that were true, then there would be a huge scrap bucket at the
factory, with most of the product coming off the line failing.
Sure there is a higher failure rate in infancy than in
the middle of life, but the highest failure rate is at the end of
life when they are almost all failing.
IDK what the difference here is between technically correct and
Life expectancy of a halogen in normal service is determined by filament
temperature (ie voltage) and hours of operation. Monitor for high
voltage or voltage variations that cause intensity to change. If on a
properly wired circuit, that bulb should not change intensity even as
other major appliances power cycle.
An abnormal event is, for example, traffic on a floor above that bulb.
Incandescent bulbs fail pre-maturely with vibrations only when hot
50 bulbs on 3 circuits - 2 on each of 2 circuits have failed within
less than 6 weeks. No electrical problems - voltage varies less than 5
volts over a typical day. No heavy equipment loads except for the AC -
which runs on a different panel. All the fixtures have magnetic
transformewrs (not switch mode) It is a single story building built
On Tue, 13 Sep 2016 21:19:29 -0700 (PDT), Uncle Monster
Built as a commercial strip plaza, converted at time of construction
to high end office space - 7 years old. Has never had incandescent
lighting. Has some "U" shaped flourescents - have replaced, if memory
serves me correctly, 3 of them There are some incandescents in
washrooms and "accent lighting" as well as a Chandelier - I've
replaced half of the bulbs excluding the chandelier, and quite a few
in the chandelier - havesince relamped it with LEDs - have had a few
failures, bur not a high rate They are base down. I don't have the
brand of the halogens handy but they were purchaced from my normal
electric supply house, Torbram Electric.
The fixtures are mounted in suspended ceiling, vented to the open
space above (minimum 4 feet clearance to roof decking)
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
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.
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.
Now you can go back happily condescending about all
our typos, not yours, of course.
And yes, I had to study all the above shit.
On Wednesday, September 14, 2016 at 6:46:41 PM UTC-4, T wrote:
It's sure odd that you made the same "typo" four times in a row
in the same post and never once got it right. What are the odds
What a buffoon. The measurement interval is exactly that, how long the
system if being measured for failures. You have a jet engine being tested,
you clock how long it is before a failure occurs. Typically it's measured
in hours, but it's not "one hour", it as long as the test goes on,
which is typically tens of thousands of hours. And your own reference
says it can be measured in miles, cycles, etc. How does that translate
to your "one hour"? So, even your own cite says you don't know what
you're talking about.
There is much more to
Intervals other than an hour would require
So we can only test light bulbs, LEDs, jet engines for a measurement
interval of one hour? Good grief
Use the MWBT (Mean Words Between Typos) formula [See Appendix E], just
add up all of the words in intervals between the starting typo and
between subsequent typos and divide by the number of typo events
recorded excluding the starting typo. It comes to about 14.33 WPT
(Words Per Typo) I think.
Be advised, small data sets may give suboptimum results and excluding
the 'warm-up' period and the 'past bedtime' period is recommended for
the best results.
Not just "how long the system if[sic] being measured for failures", but
where. The idea is to exclude the outliers of 'infant failure' and
'system age wearout' by getting the data set from the steady rate of
midlife operation from the nearly flat bottom of the bathtub curve.
It would certainly speed up the process, and marketing would just love
the great looking numbers. No need to test them for *two* hours when
you get such good results from one hour.
> trader_4 has brought this to us :
> <snip> quoted Left Wing drivel </snip>
On 09/15/2016 12:27 PM, FromTheRafters wrote:
I once asked how the military came up with the numbers.
I don't remember exactly what I got back, but the
term "Fudge Factor" had to apply. I do believe they
did things like speed up aging by heating the guys and then
used formulas to extrapolate the numbers back to room
temperature. Different types of parts had different
formulas. Iron versus silicon, for instance.
Or something like that.
Here is a good example of where MTBF means nothing:
"Life Expectancy: 1.2 million hours Mean Time
Between Failures (MTBF)"
Does anyone actually think that the average lifespan is
137 YEARS? Oh brother. The metal would corrode by then.
The silicone in the transistors would start dripping
and turning back into glass.
The real "Life Expectancy" would be the warranty, which
is five years. And five years is good for such drives.
But 137 years does sound a lot better to the marketing
Hmmm. I wonder if I made any typos. AAAAAHHHHHHH !!!!
It's about using the right tool for the right job and not confusing
mathematical predictions with actual empirical measurements.
Marketing can use engineering numbers to confuse and confound end users
who think units were actually tested for 274 years on a test bench and
half-life used as a conservative measure of life expectancy.
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