[time-nuts] Updating the unit of,time: the second.

[Attila Kinali]

On Tue, 28 May 2019 03:06:12 +0100
"Dr. David Kirkby" <drkirkby at kirkbymicrowave.co.uk> wrote:

> I notice a lot of 1 kg weights on eBay, so perhaps the same will happen
> with Cs clocks!

This is rather unlikely. For one, Cs beam standards have a very limited
life span. For an other I am pretty sure that the surge of kg weight
standards on ebay is due to their manufacturing becoming cheap rather
than the kg definition changing. Most of these standards are M1 or M2
anyways (or in other words, they are accurate to 50ppm or 160ppm
respectively [1]), which is way more than the slight change in the 
definition of the kg. 

Another way to look at it is, before you reach the point where the
redefinition of the kg change becomes visible, other errors like
buoyancy of air will introduce errors that are orders of magnitude
largers (uncorrected the buoyancy induced uncertainty is IIRC in the
a few ppm range, corrected its induced uncertainty goes to 1e-8).
So, unless you are doing your weight measurements in vacuum, there is
no need to care about the change of definition of kg.

If we look at frequency standards, then using a simple L1-only GPSDO
brings us to better than 1e-10 for τ > 1s. If you do PPP frequency
transfer as Ole did, you get to 1e-11 for τ > 1s and down to 1e-14
for τ > 1000s. And all that with a very moderate budget. Why spend
thousands of € for a surplus Cs beam that will be out of Cs fumes in 
5-10 years, when I can build a similar quality standard for a fraction
of the cost that is probably going to work for decades to come?

			Attila Kinali

[1] OIML R111-1
https://www.oiml.org/en/files/pdf_r/r111-1-e04.pdf
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