[time-nuts] Fw: Rb Oscillator - rather fundamental question
Lux, Jim (337C)
james.p.lux at jpl.nasa.gov
Tue Feb 23 21:13:17 UTC 2010
> -----Original Message-----
> From: time-nuts-bounces at febo.com [mailto:time-nuts-bounces at febo.com] On Behalf Of WarrenS
> Sent: Tuesday, February 23, 2010 1:04 PM
> To: Discussion of precise time and frequency measurement
> Subject: [time-nuts] Fw: Rb Oscillator - rather fundamental question
> One more try, As often happens when I rant, the rant is discarded in the
> Thanks, Interesting but maybe you have missed my too subtle of a point.
> Lets say the second is redefined in the future to some new super duper thing
> that is good to 1 part in e20
> (Which will happen if (when) the super duper thing becomes more available
> and proven)
> (Maybe based on the time it takes to count all the atoms in the new purposed
> 1 Kg sphere OR something like that.)
> Then the CS Osc would not be the BEST primary standard anymore, at least NOT
> at the new improved spec it could then be given.
> Not because it has changed or is less accurate, but because there is now
> something better.
> If it is not the primary standard, it does not make it worse, but it does
> mean it will now be a second standard at the new higher performance spec, by
> definition and need to be then calibrated and checked against the new
> primary standard IF one wanted to use it to it's maximum capability as a
> cost effective substitute for the supper duper.
I don't think so..
In that event, the unobtainium and Cs sources would both be primary standards (within their random variation).
The Cs+ standard would be less accurate than the Un+ standard, but they're both primary.
The key to a primary standard is that if you build it, it requires no calibration against something else.
It's like the meter, which is defined in terms of the wavelength of a particular spectral line in vacuum. Doesn't matter how you get the spectral line, but count off some number of wavelengths, and that's a meter.
Now, could one argue that a Rb source is also a primary standard, just with low precision?
More information about the time-nuts