https://ohwr.org/project/white-rabbit/wikis/Oct2022Meeting
"Precision Time Sync in Datacenters and potential applications for WR and Time Appliances Project"
by Ahmad Byagowi explains why NTP is not sufficient and the benefits of
PTP (White Rabbit) for synchronizing distributed data storage in their
data centers.

Best, JM

I used IEEE1588 (PTP) to achieve tight time sync between devices on the same network for the Perceptron AccuGauge ACF system: https://www.youtube.com/watch?v=JkaWx_w0-M8

In a nutshell, the “cage" on the robot arm has LEDs at each vertex, and the bar has three linear cameras watching the scene. The LEDs are flashed sequentially and image captures are taken at the same time, and then after an enormous amount of math and other secret sauce I don’t pretend to understand, you get 9DOF measurements out the other side. Tight (I was aiming for 60ns, I think it was relaxed to 1 or 2us before the product was released) timing was needed to make sure the cameras were “looking” when the light was on, and when you’re trying to hit 5000 measurements/sec it’s important that you don’t spend too much time on any single LED.

In fact this project was why I joined time-nuts.

-A.

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.  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.

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.

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.

--
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?

Hello,

Sync-Ethernet and PTP is used in 5G and other networks, such as stock exchanges (High frequency trading, where computers automatically make decisions regarding trades). G.8275.1 seems to be choice now.
I hope no one minds but the book is very good and covers these topics very well..

https://www.ciscopress.com/store/synchronizing-5g-mobile-networks-9780136836254

regards,

Peter

On 29/11/2022, 15:28, "Eric Scace via time-nuts" time-nuts@lists.febo.com wrote:

PTP is used in digital radio and TV studios and in the distribution of studio programming to transmitter sites. 

Sent from my iPhone

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The kilogram was sorted a couple of years ago.
It is now defined in terms of teh Planc constant which has been declared as
a fixed value
All the other SI units are defined the same way now - by fixing the
physical constants  = and all referring back to the second.

https://physicsworld.com/a/new-definition-of-the-kilogram-comes-into-force/#:~:text=The%20kilogram%20is%20now%20defined,such%20as%20the%20Kibble%20balance
.

Andy
www.g4jnt.com

On Tue, 29 Nov 2022 at 19:33, Oz-in-DFW via time-nuts <
time-nuts@lists.febo.com> wrote:

On 11/29/22 11:36 AM, Andy Talbot via time-nuts wrote:

Isn't the volt defined in terms of a Josephson junction, and frequency,
which is in terms of time, again.

The volt isn’t an SI unit. The amp is, and volts will be derived from amps
via power which itself comes from mass, length and time.

On Tue, 29 Nov 2022 at 21:59, Lux, Jim via time-nuts <
time-nuts@lists.febo.com> wrote:

--
Andy (out keeping fit)

On 11/29/22 2:02 PM, Andy Talbot wrote:

The volt is not a base SI unit, true, but the SI definition depends on
the Josephson constant.

The amp is defined in terms of charge on an electron 9defined as
1.602... E-19 coulombs) and electrons per second (which is back to
accurate time message).

On Tue, 29 Nov 2022 at 13:15, Hugh Blemings hugh@blemings.org wrote:

I can’t see how knowing who posted what first on Facebook, Instagram etc
affects the user experience, when differences in time are any less than a
second. So I am not convinced that timenut-grade oscillators are needed for
that purpose!  I don’t know if accurate timing is important for network
security.

As far as I am aware, of the 7 base SI units (metre, second, kelvin,
candela, ampere, kilogram and mole), the second is the only SI base unit
where low uncertainty is important to a large number of people. The
instances where it is important seem to be limited to

• Navigation systems (eg GPS)
• Telecommunications
• Financial transactions.

Sure, timing is important for radio astronomy as someone mentioned, but
that doesn’t have any practical impact to many people.

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

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

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

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

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@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