[time-nuts] Primary Time Standards

[Bob Camp]

Hi

If you are running a Cs at high altitude, or worse yet in space -
relativistic effects are pretty significant. 

Bob

-----Original Message-----
From: time-nuts-bounces at febo.com [mailto:time-nuts-bounces at febo.com] On
Behalf Of Poul-Henning Kamp
Sent: Thursday, July 14, 2011 10:04 AM
To: Discussion of precise time and frequency measurement
Subject: Re: [time-nuts] Primary Time Standards

In message
<CALH-g5YuKCDiyGxDf4s-MhHtK=dS7Qr8z2st17jrqiLwVR0XoA at mail.gmail.com>
, Jim Palfreyman writes:

>Primary Standards are ones which don't have to be calibrated against
others.
>My understanding is that Caesium and Hydrogen masers are Primary Standards
>(in our field).
>
>Secondary Standards are calibrated against the Primary Standards. My
>understanding is that Rubidium is an example of a Secondary Standard.

Almost, but not quite.

Primary standards run at an intrinsic freqyency which is determined
by the atomic/physical principle used.

Secondary standards run at a frequency which is different from unit
to unit due to side-effects from the physical principle used.

Rule of thumb:

If the timekeeping atoms are not in vaccuum, it's not a primary std.

>But why is it that Caesium Clocks and Hydrogen Masers have an adjustment
>facility?

Because there are external effects that need to be cancelled out,
mainly the magnetic field from the earth.

-- 
Poul-Henning Kamp       | UNIX since Zilog Zeus 3.20
phk at FreeBSD.ORG         | TCP/IP since RFC 956
FreeBSD committer       | BSD since 4.3-tahoe    
Never attribute to malice what can adequately be explained by incompetence.

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