[time-nuts] nubie querie

[paul swed]

OK then if you ground up cesium azide and put it in the hour glass wouldn't
you have a cesium clock at much lower cost (And accuracy) then an HP??
Might last quite a while also.

On Fri, Mar 5, 2010 at 1:53 PM, Tom Van Baak <tvb at leapsecond.com> wrote:

> Even defining when the sand timer is "done" is not a real
>> simple thing. Waiting for that very last particle to drop may
>> not be the best approach.
>> Bob
>>
>
> Correct. Marking time with an hour glass is not that different
> from marking time with a 1PPS. Each signal has a rise time;
> one picks the appropriate live trigger level or sampled slope
> waveform model to minimize jitter.
>
> Waiting for the last grain is like waiting for the last millivolt of
> a TTL 1PPS pulse; no one does that.
>
> Note that [this] hourglass interval has a standard deviation on
> the order of 10 seconds. So my initial goal is 1 second timing
> resolution, which turns out to be pretty easy to do optically.
>
> Whether sand or cesium, phase comparators have a minimum
> resolution. While lower resolution is better, if the ADEV of the
> DUT is too far above the ADEV of the comparator then that
> resolution is wasted. So detection to a granularity of 1 second
> is sufficient for this application.
>
>
> /tvb
>
>
>
>
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