[time-nuts] Re: What everyday uses are there for accurate clocks?

[Dr. David Kirkby]

On Tue, 29 Nov 2022 at 19:34, Oz-in-DFW via time-nuts <
time-nuts at lists.febo.com> wrote:

> On 11/28/2022 8:45 PM, Dr. David Kirkby via time-nuts wrote:
>
> Aside from Communication and astronomy, accurate time is a fundamental
> measure used in the establishment of many other dimensions. Current and
> Length are both defined with time as component.  Improved accuracy of
> time improves the accuracy of those other measures.


Yes, but for the vast majority of the population, highly accurate current
measurements or length measurements are not important.

I believe the only  measure that uses a physical item as it's reference is
> mass in the form of /*the */kilogram, and there is a lot of work going into
> eliminating
> that need.


That nut was cracked three years ago. No longer is the kilogram defined by
a bit of metal in a vault in Paris. Here’s a cut and paste of the
definition from a booklet on the topic by NPL.

The kilogram is defined by taking the fixed numerical value of the Planck
constant, ℎ, to be 6.626 070 15 × 10-34 when expressed in the unit J s,
which is equal to kg m2 s−1, where the metre and the second are defined in
terms of the speed of light, 𝒸, and the hyperfine transition frequency of
the caesium-133 atom, ∆ν, respectively.

This was a new definition in May 2019.

https://www.npl.co.uk/si-units/kilogram



> As for things that need accurate clock, the question becomes how accurate?
>
> If we use "better than NTP" as a reference there are a host of
> industrial applications that synchronize machinery.  High speed roll
> fed multistage printing presses need to have the stages synchronized to
> prevent from piling paper up, or shredding it.  Any similar process flow
> of continuous material needs PTP level synch - so wire drawing, metal
> sheet mills, paper mills, and so on.  Older versions of these used
> timing shafts which limited ramp rates and had propagation problems
> related to shaft flexure that limited the size of systems. Application
> of mechanical buffers was used to some degree, but they have their own
> problems.


None of them seem to be pushing the boundaries of what could be achieved
with a decent undisciplined crystal oscillator.

>
>
> Traffic flow management like trains and highways require far higher
> accuracy than I expected. It's required to maintain safety at high flow
> rates and optimize capacity. The incremental cost of rail capacity is
> not small. I expected the need to be ~10 sec accuracy and its often more
> like 10 milliseconds for high volume passenger rail and highways.


I am surprised by 10 ms, but that’s many orders of magnitude larger than
state of the art


Dave.
-- 
Dr. David Kirkby,
Kirkby Microwave Ltd,
drkirkby at kirkbymicrowave.co.uk
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