[time-nuts] Rubidium standard

Steve Rooke sar10538 at gmail.com
Wed Nov 18 10:22:04 UTC 2009


Dave,

The point I should have made is that most quoted MTBF figures have a
reasonable bearing on the lifetime of the item, this example was well
off given the inbuilt expiry dates of humans. In addition, a lot of us
are using equipment that is well past it's use by date and it keeps on
going, humans can't (at present) be repaired to last 600 years. I
believe the lifetime of the machine is related to the usability of the
item and you can't just assume that the item will just fail at 1
second past the MTBF. If the item fails early on, it can frequently be
repaired and then continue to perform for the expected lifetime.
Reports from other members of the group who have repaired rb units
seem to support this.

Manufactures can only give us some idea of how long their devices
should be expected to last and the only real tool that gets anywhere
near being practical is the MTBF. This enables us to plan the for the
reasonable expected lifetimes of the systems we build and the
maintenance swapouts/upgrade plans. If any manufacturer starts giving
out very optimistic MTBFs then they will surely get a lot of negative
feedback from their customers and probable loss of business due to
loss of trust.

I felt that an example based on humans was not really applicable to
the real world of electronic items but that is my own opinion and I'm
happy if you disagree with me.

Cheers,
Steve

2009/11/18 David C. Partridge <david.partridge at dsl.pipex.com>:
>>The failure rate of a human is not constant over the lifetime and just
> taking a figure at the age of 25 will get you nowhere.
>
> Steve,  I think you'll find that's a total red herring.
>
> That's because if you measure failure rates of almost anything, you will
> find that the failure rate varies over their life time, increasing as they
> get older, often very dramatically in the final stages ...
>
> Now we can argue about "life-time" and such, but the point that Mike S was
> making that lifetime != inverse MTBF is still very true, and the example
> wasn't all that bad either.  I can't think of many manufactured things that
> don't have a lifetime that is unrelated to MTBF figures early in their life.
>
> Dave
>
>
> _______________________________________________
> time-nuts mailing list -- time-nuts at febo.com
> To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
> and follow the instructions there.
>



-- 
Steve Rooke - ZL3TUV & G8KVD
A man with one clock knows what time it is;
A man with two clocks is never quite sure.



More information about the time-nuts mailing list