[time-nuts] Sneaky Errors

[Chris Albertson]

On Wed, Oct 19, 2011 at 12:46 PM, David VanHorn <
D.VanHorn at elec-solutions.com> wrote:

>
> I have two thunderbolts, set up so that I can switch over to the backup
> unit if the primary fails.
> All is well with that, but what could I do to detect a less obvious
> failure, like 9.999999 MHz output?
>
> If they disagree, I don't know how to resolve which is correct.
>

The only way is to have third or fourth 10Mhz oscillator.  If you are very
conservative or if this is for some critical requirement then I'd get
something other than another TB.  It is always remotely possable that the
reason for out of spec performance is a design flaw. Having three identical
units would never catch this kind of problem as it would hit all three at
the same time.    Using that same line of logic.  Maybe your
third redundant standard should not depend on GPS.   I'd say you might want
a Rubidium.   Then you compare all three periodically check that the two TB
track each other and that the Rb drifts slowly away.   Later if ever the two
TBs fail to track each other you will need all that drift data you collected
to figure out which TB is "correct" because it's only 50/50 that the correct
TB would be the one closest to the Rb.

>
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-- 

Chris Albertson
Redondo Beach, California