[time-nuts] MTBF (was Rubidium standard)
Mike S
mikes at flatsurface.com
Wed Nov 18 19:06:55 UTC 2009
At 01:14 PM 11/18/2009, Michael Sokolov wrote...
>As I have learned in school from a department head, mean time between
>failures (MTBF) means anything only if you are being mean. If you are
>not being mean, it means nothing.
There is at least one practical use for MTBF, at least the real-world
statistical form.
If one has a reasonably large population of devices to maintain, the
number of spare devices needed to stay operational is a function of the
MTBF.
If you've got 10,000 cell sites, each with an Rb timebase, MTBF figures
can provide a pretty accurate estimate of how often one will fail and
need to be replaced, at least during the normal lifetime (between the
infant mortality and wearout stages). Coupled with MTTR statistics, one
can figure out how many spares should be stocked.
Manufacturers invest a lot of effort into using such statistical
measures to determine how many spare parts should be kept at various
points in the supply chain. Unnecessary parts on shelves = wasted
capital. Manufacturers also use MTBF statistics to price service
contracts on equipment.
This only works when one is dealing with a large population of devices,
so MTBF is meaningless at the individual unit level.
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