[time-nuts] Rubidium standard
Mike S
mikes at flatsurface.com
Thu Nov 12 12:50:44 UTC 2009
At 03:31 AM 11/12/2009, David Smith wrote...
> The LPRO-101 blurb says:
> Amb.Temp: 20 °C 25 °C 30 °C 40 °C 50 °C 60 °C
> MTBF (hrs) 381k 351k 320k 253k 189k 134k
>
> A year is 8760 hours (ignoring leap
> years). Call that 10K. So they
> expect
> 25 years at 40C and 32 years at 30C.
>
> That's calculated MTBF. YMMV.
I'm sure someone with more statistics background
can add to this, but useful (or expected)
lifetime cannot be determined from an MTBF number.
Here's an example I found, demonstrating this:
"There are 500,000 25-year-old humans in the sample population.
Over the course of a year, data is collected on
failures (deaths) for this population.
The operational life of the population is 500,000
x 1 year = 500,000 people years.
Throughout the year, 625 people failed (died).
The failure rate is 625 failures / 500,000 people
years = 0.125% / year.
The MTBF is the inverse of failure rate or 1 / 0.00125 = 800 years.
So, even though 25-year-old humans have high MTBF
values, their life expectancy
(service life) is much shorter and does not correlate."
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