On 11/29/2022 5:36 PM, Dr. David Kirkby wrote:

Depends on how you scope the problem.  They are essential to everyday
life if you look at the items in the average first world household.

I understood the original question was essentially "why is this
relevant"  not how do I use this directly?

Low power electronics often requires 9 orders of magnitude of current
measurements.  The individuals holding a cellphone may not make those
measurements, but they rely on them every day.

Modern mechanical parts routinely rely on accuracy of a few tens of
microns. Again, not necessarily a measurement that someone is likely to
make, but any modern item relies heavily on that level of accuracy.

Rich

--
mailto:lists@ozindfw.net  http://www.ozindfw.net
Oz;  POB 93167; Southlake, TX 76092 (Near DFW Airport)

If electricity comes from electrons, does morality come from morons?

Hi Dave, All,

On 30/11/2022 04:45, Dr. David Kirkby wrote:

A fair point - I was merely striving for end user friendly examples of
why consistent (if not necessarily sub-second) accurate timekeeping
might matter to them :)

All of the SI units depend on the second, except for the mole, which is
defined by the Avogadro constant.

Cheers
Michael

On Wed, 30 Nov 2022 at 8:59 am, Lux, Jim via time-nuts <
time-nuts@lists.febo.com> wrote:

On Tue, 29 Nov 2022 22:02:19 +0000
Andy Talbot via time-nuts time-nuts@lists.febo.com wrote:

While it is true that the SI unit is Ampère, the mise en pratique
for electrical units is done using a Josephson junction for the Volt
and a fractional Hal effect system for the Ohm. The Ampère is then
realized using a calibrated voltage and resistance. Why? Because
the Volt and Ohm can be accurately realized by quantum mechanical
systems that are impervious to small changes in their environment.
While the old definition of the Ampère was very hard to realize and
thus was never really used that way. This is also reflected in the
redefinition of 2019, which allows Volt and Ohm to be precisely calculated
using quantum mechanical relations and thus allow the for an exact
realization of the Ampère when going backwards.

But this is going into volt-nuts territory. Please ask there if
you want to know more.

		Attila Kinali

--
Science is made up of so many things that appear obvious
after they are explained. -- Pardot Kynes

I think some may be missing one of the main reasons...  GPS was initially
created for one main reason.  To more accurately locate, track, and
potentially eliminate adversaries.  We love all the side benefits but our
system and competing countries, for the most part, have one primary use
case.  Today for us in the US it's M-code and BlockIII satellites to
advance our positioning.  A-PNT aka assured position navigation and timing
are the focus.  How do we defend against jamming, spoofing, or compete
denial of our beloved GPS sat signals and make sure they're distributed in
a denied environment?  🤔

Bill

On Tue, Nov 29, 2022, 2:31 AM Dr. David Kirkby via time-nuts <
time-nuts@lists.febo.com> wrote:

On Wed, 30 Nov 2022 at 02:01, Oz-in-DFW lists@ozindfw.net wrote:

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

Depends on how you scope the problem.  They are essential to everyday life
if you look at the items in the average first world household.

I understood the original question was essentially "why is this relevant"
not how do I use this directly?

Low power electronics often requires 9 orders of magnitude of current
measurements.  The individuals holding a cellphone may not make those
measurements, but they rely on them every day.

Modern mechanical parts routinely rely on accuracy of a few tens of
microns. Again, not necessarily a measurement that someone is likely to
make, but any modern item relies heavily on that level of A
Rich

Thank you. That’s a very good answer. It encapsulates why accurate
measurements are needed for everyday use.

However, the relative uncertainty of time/frequency measurements is orders
of magnitudes lower than those of distance, temperature, current,
luminosity etc. So improvements in frequency standards will not improve our
ability to measure voltage, distance, temperature etc. I checked the NPL
website but could not see a figure for their relative uncertainty on
voltage measurements, but I know it will be orders of magnitude higher than
frequency. Even the best multimeters are “only” 8.5 digits, but frequency
counters have 12 digits.

Dave

Dr. David Kirkby,
Kirkby Microwave Ltd,
drkirkby@kirkbymicrowave.co.uk
https://www.kirkbymicrowave.co.uk/
Telephone 01621-680100./ +44 1621 680100

Registered in England & Wales, company number 08914892.
Registered office:
Stokes Hall Lodge, Burnham Rd, Althorne, Chelmsford, Essex, CM3 6DT, United
Kingdom

On Wed, 30 Nov 2022 at 09:21, Attila Kinali via time-nuts <
time-nuts@lists.febo.com> wrote:

The volt is not one of the 7 base SI units, but  it is one of the 22
derived SI units with special names. See section 2.3.4 of

https://www.bipm.org/documents/20126/41483022/SI-Brochure-9-EN.pdf

Dave

Why? Because

--
Dr. David Kirkby,
Kirkby Microwave Ltd,
drkirkby@kirkbymicrowave.co.uk
https://www.kirkbymicrowave.co.uk/
Telephone 01621-680100./ +44 1621 680100

Registered in England & Wales, company number 08914892.
Registered office:
Stokes Hall Lodge, Burnham Rd, Althorne, Chelmsford, Essex, CM3 6DT, United
Kingdom

I used to work in this industry (industrial power electronics) and that was achieved through encoders on the spool shafts and computing the correct turning speed (as paper spooled or unspooled) rather than timing. The speed control of the motors driving those spools was done through VFDs (these were the types of product I designed) and their clock accuracy was no better than whatever off the shelf crystal or oscillator we put in them. We definitely didn’t need TCXO or clock sync between drives, but they were definitely networked and the higher level PLC kept the speeds within spec. There were also mechanical devices (web tensioners) which did the lion’s share of the work in keeping the paper correctly tensioned as it moved through the process.

-A.

They don't use tight time synchronization because they care about event
ordering as presented to the users (and all these social networks have
basically abandoned chronological feeds anyway, for improved addiction
susceptibility of their products). What does matter in this context is that
the massively distributed database cluster agrees on the order of updates
to its data structures, lest different nodes see a different, possibly
invalid, state. Very precise time sync means that instead of using locking
(blocking writes while reads occur) or a time oracle, it's feasible to use
'wall clock commit time' to order updates, which really simplifies and
improves performance and scalability of these systems. Google has more on
this in their TrueTime documentation:
https://cloud.google.com/spanner/docs/true-time-external-consistency

In this context of cloud-scale stuff, justifying PTP for it might be a
stretch, but it is also useful to have enough precision that timestamps can
resolve order of events across the large distributed system for tracing
purposes. Initial packet arrives at router, 100us later the OS receives it
and routes it to the application socket, 5ms later a related call is made
out to a distributed DB, this packet is launched at t+5.1ms and so on.

On Tue, 29 Nov 2022 at 23:01, Dr. David Kirkby via time-nuts <
time-nuts@lists.febo.com> wrote:

I didn't read the whole thread so I may have missed some past answers. However one example I may give for " What everyday uses are there for accurate clocks" is the one about TDD phase/time synchronization for TDD 4G/5G base stations: equipments on the same channel (same operator, or different operators across a border) or on adjacent channels within the same band all need to transmit at the same time and receive at the same time (otherwise the cross-link BS-BS interference vastly outscales what 3GPP RAN4 has specified, and specific measures need to be taken - but 5G base stations no longer enable the possibility to add custom operator-specific cavity filters...). You may have a look at https://docdb.cept.org/download/1160

In order to transmit/receive at the same time, all equipments from all operators must use on a common clock (typically traceable to UTC), with an accuracy of +/-1.5 µs (as specified by 3GPP). This is often done with GPS, but all the standards from ITU-T Q13 (PTP, SyncE...) enable to transfer time across a network which alleviates the need for a GPS receiver at each site (or the need to shutdown the site if its GPS receiver gets jammed. Unfortunately more and more GPS jamming events are observed despite it is highly illegal... :-/ ). Having a high quality local oscillator in base stations enables to keep it in free-run for a longer holdover time in the case of such a GPS jamming event (since it will take longer until the +/-1.5µs budget is exceeded).

--
Adrien

----- Mail original -----

De: "Clint Jay via time-nuts" time-nuts@lists.febo.com
À: "Discussion of precise time and frequency measurement" time-nuts@lists.febo.com
Cc: "Dr. David Kirkby" drkirkby@kirkbymicrowave.co.uk, "Clint Jay" cjaysharp@gmail.com
Envoyé: Mardi 29 Novembre 2022 10:50:28
Objet: [time-nuts] Re: What everyday uses are there for accurate clocks?

I believe radio and television broadcasting makes use of accurate time in
studio and the wider transmission network.

I've worked in quite a few data centres where there's been a local NTP
server that was synced to GPS or, prior to the availability of GPS, the
"local" broadcast time signal.

On Tue, 29 Nov 2022, 09:29 Dr. David Kirkby via time-nuts, <
time-nuts@lists.febo.com> wrote:

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