[time-nuts] Primary Standards...

Bob Camp lists at rtty.us
Wed Feb 24 17:33:27 UTC 2010


Hi

One significant point there about BIPM - "earth rotation measurements". UTC
is not a straight count of "standard" seconds. Somebody has to decide when
to slip it to match our wobbly planet. Not because of an error in the
second, it's the planet that's not stable enough...

------

Stuff that's more exotic than a Cesium tube does exist. The problem - you
can't afford to run one for very long. Even with a government paying the
bills that's true of a lot of this stuff. A clock that you can't run
continuously is not a real good thing to depend on. 

I'd bet at least a dollar that we'll be using Cesium for quite a while.

Bob




-----Original Message-----
From: time-nuts-bounces at febo.com [mailto:time-nuts-bounces at febo.com] On
Behalf Of Rob Kimberley
Sent: Wednesday, February 24, 2010 7:38 AM
To: 'Discussion of precise time and frequency measurement'
Subject: Re: [time-nuts] Primary Standards...

Yes, and no..

Time as we know it (UTC) is coordinated at the BIPM in Paris between
observations from primary standards at contributing laboratories and also
earth rotation measurements. Each lab contributing will at any time (excuse
the pun) have a small time offset with regard to UTC. E.g. time from NPL in
UK would say be offset from UTC at any time by a few microseconds, and would
be designated UTC-NPL. Worth reading
http://www.npl.co.uk/science-technology/time-frequency/time/

Interestingly there is a lot of research into more stable clocks using
Mercury and Ytterbium. This then leads to discussion about a future possible
re-definition of the second (which IMHO will happen).

Rob Kimberley

-----Original Message-----
From: time-nuts-bounces at febo.com [mailto:time-nuts-bounces at febo.com] On
Behalf Of Mike S
Sent: 24 February 2010 12:14 PM
To: Discussion of precise time and frequency measurement
Subject: Re: [time-nuts] Primary Standards...

At 07:46 PM 2/23/2010, Rick Karlquist wrote...

>The TAI is a weighted average to improve short term stability and
>to average out random frequency errors.

IOW, there is a variance from clock to clock. So, if there are 80 
different clocks, are there 80 different seconds, or 80 imperfect 
clocks? Is this a problem with the definition (i.e. Cs resonance is 
unstable), or with the clocks?


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