[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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