Hi,
On 05/07/2015 11:48 PM, Bob Camp wrote:
Hi
On May 7, 2015, at 8:02 AM, Pete Stephenson <[email protected]> wrote:
On 5/7/2015 1:22 PM, Bob Camp wrote:
Hi
I guess on a general level:
1) How do they generate the Swiss version of UTC (fleet of hydrogen masers run
into to a .. :)
According to their website they use an ensemble of commercial cesium
clocks (they show some photos of HP 5071As) and a hydrogen maser. I'll
be sure to ask them for details.
2) How do they link that version of UTC with the rest of the world? (BIH etc)
BIH = Bureau International de l’Heure
They are the people who (by treaty) decide what time it *really* is. In order
to do this they need to
be able to evaluate the various time scales around the world. That evaluation
process requires some
method of direct inter comparison of time scales over very long distances.
Typical approaches range
from “clock trips” to TWSTT ( or TWSTFT) to GPS based techniques.
As I recall it, they do no longer check the time-scales alone, but
report the time difference of all their clocks in relation to their
time-scales, such that TAI gets calculated out of all available clocks.
Actually, they first produce another time-scale from all clocks for
optimum stability and then frequency correct it into TAI and from that
uses the leap-second to produce UTC. Typically each lab run their own
ensemble algorithm and then use one of their clocks to feed a
microstepper that then produces the UTC(lab) of that lab. Some also
produces a TAI equivalent in the form of TA(lab). The algorithm steering
the microstepper also get's fed corrections from the UTC calculations in
order to steer the labs UTC to be inline. This is also used to steer
slave-clocks such as the GPS clock to be inline with USNO (if they
haven't changed anything in the details).
Knowing this overall process helps in understanding what you see and ask
the questions.
In addition to the comparison process it’s self, there is also a lot of
internal cross checking and analysis
that goes into a typical time scale. Often the associated equipment base is
pretty substantial. It’s also a
good thing to look at to pick up ideas for (lower cost) implementation in a
basement lab.
Indeed.
Cheers,
Magnus
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