Discussion:
A different timenuts interest
(too old to reply)
Morris Odell
2010-07-22 00:13:24 UTC
Permalink
Hi all,

I have been asked to help with the construction of a Foucault pendulum. This
is a long pendulum which oscillates in a slow stately fashion in a fixed
plane which appears to move as the earth rotates. In reality the surrounding
environment is really moving relative to the plane of oscillation.

The pendulum requires a sustaining system to compensate for the inevitable
energy loss with each swing. The system is located in the building and
therefore rotates relative to the pendulum. It needs to provide an impulse
which does not affect the plane of oscillation of the pendulum. I was
thinking of an electromagnet located below the centre of the swing which
would be pulsed appropriately as the bob passes over it.

Has anyone here had any experience with such a system of have any
suggestions regarding the sustaining system? This is an interesting and
challenging project.

Cheers,

Morris
J. Forster
2010-07-22 00:29:06 UTC
Permalink
The problem is straight forward, except for sensing the position of the
pendulum so the impulse is applied at the correct phase.

There must be a bunch of published designs, but if I were to try it, I'd
use something optical or capacitive.

For optical, I'd put a annular ring of IR LED/Phototransistor assemblies
around the center, wired OR the outputs, and use the signal to trigger the
impulse. The bottom of the pendulum should be polished or mirrored.

For capacitive, I'd copy a "proximity detector" circuit and use that. One
plate would be the pendulum, the other an annular conducting ring just
below it. It might also work with two, concentric rings and an
electrically isolated pendulum.

Best,

-John

===========
Post by Morris Odell
Hi all,
I have been asked to help with the construction of a Foucault pendulum. This
is a long pendulum which oscillates in a slow stately fashion in a fixed
plane which appears to move as the earth rotates. In reality the surrounding
environment is really moving relative to the plane of oscillation.
The pendulum requires a sustaining system to compensate for the inevitable
energy loss with each swing. The system is located in the building and
therefore rotates relative to the pendulum. It needs to provide an impulse
which does not affect the plane of oscillation of the pendulum. I was
thinking of an electromagnet located below the centre of the swing which
would be pulsed appropriately as the bob passes over it.
Has anyone here had any experience with such a system of have any
suggestions regarding the sustaining system? This is an interesting and
challenging project.
Cheers,
Morris
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jimlux
2010-07-22 04:02:39 UTC
Permalink
Post by J. Forster
The problem is straight forward, except for sensing the position of the
pendulum so the impulse is applied at the correct phase.
There must be a bunch of published designs, but if I were to try it, I'd
use something optical or capacitive.
For optical, I'd put a annular ring of IR LED/Phototransistor assemblies
around the center, wired OR the outputs, and use the signal to trigger the
impulse. The bottom of the pendulum should be polished or mirrored.
The usual scheme is a couple of optical paths at the top of the pendulum
with lenses to focus the beam down to a very small diameter (smaller
than the wire diameter). The two optical paths are at 90 degrees to
each other, and are logically anded either by using a pair of
detectors/paths, or by using a mirror to fold the path.

It's aligned with the pendulum perfectly stationary (i.e. it's been
sitting still for a day or two) so the beam trigger occurs precisely at
the center point.
Magnus Danielson
2010-07-22 00:50:03 UTC
Permalink
Post by Morris Odell
Hi all,
I have been asked to help with the construction of a Foucault pendulum. This
is a long pendulum which oscillates in a slow stately fashion in a fixed
plane which appears to move as the earth rotates. In reality the surrounding
environment is really moving relative to the plane of oscillation.
The pendulum requires a sustaining system to compensate for the inevitable
energy loss with each swing. The system is located in the building and
therefore rotates relative to the pendulum. It needs to provide an impulse
which does not affect the plane of oscillation of the pendulum. I was
thinking of an electromagnet located below the centre of the swing which
would be pulsed appropriately as the bob passes over it.
Has anyone here had any experience with such a system of have any
suggestions regarding the sustaining system? This is an interesting and
challenging project.
Just as you slightly "push away" the bob you could also attract it as it
comes back... then you get a push-pull action. A coil in the center
would have a fairly low plane-shifting action.

Cheers,
Magnus
mikes-kj5vH+ (Mike S)
2010-07-22 00:53:18 UTC
Permalink
At 08:13 PM 7/21/2010, Morris Odell wrote...
Post by Morris Odell
Has anyone here had any experience with such a system of have any
suggestions regarding the sustaining system? This is an interesting and
challenging project.
Scientific American, back in June 1958, covered many details of
Foucault pendulums, from Charron pivots to drive systems. The article
was later reprinted in "The Amateur Scientist" book. It describes a
magnetic drive which applies force near the pivot and another which
sits underneath the pendulum.

There's also a mechanical drive, as described near the bottom of this
page:
http://science-design.com/pages/foucault_pendulum_background/
Bob Camp
2010-07-22 01:17:25 UTC
Permalink
Hi

If you use the mechanical system (raise and lower the pivot point): Can you use the strain on the pivot to get the "location" information?

Bob
Post by mikes-kj5vH+ (Mike S)
At 08:13 PM 7/21/2010, Morris Odell wrote...
Post by Morris Odell
Has anyone here had any experience with such a system of have any
suggestions regarding the sustaining system? This is an interesting and
challenging project.
Scientific American, back in June 1958, covered many details of Foucault pendulums, from Charron pivots to drive systems. The article was later reprinted in "The Amateur Scientist" book. It describes a magnetic drive which applies force near the pivot and another which sits underneath the pendulum.
http://science-design.com/pages/foucault_pendulum_background/
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Hal Murray
2010-07-22 01:43:11 UTC
Permalink
... Foucault pendulum ...
Has anyone here had any experience with such a system of have any
suggestions regarding the sustaining system? This is an interesting and
challenging project.
Several years ago, I found a web site for a commercial place that made them
for museums. (I forget why I was looking for that sort of stuff.) You might
find interesting stuff/ideas via google but I didn't find a similar site with
a bit of searching.

----------

Here is what I would try:
Put a magnet on the bottom of the pendulum.
Put a coil below it. (obviously centered)

Use the coil as a sensor to measure the timing.
Use the coil as a motor to pull the pendulum every N-th swing.

The question is how accurately centered do the magnet and coil have to be? I
don't know. It sounds like a fun mixture of theory and engineering.

One of the variables is how far away is the pendulum when you are pulling.
The farther away it is, the smaller angle you have from the ideal. You can
change that by varying the start/stop times on the pull pulse.

I'd probably put the coil on a crude X-Y table, set it up as good as I could,
then see if it worked. Then I would deliberately move it off a bit and see
what happened. Or try to servo it to the best place, probably by manual
changes every day or week or ???

I'm assuming this is for a school or museum. The required positional
accuracy is actually a real science experiment. The idea of "experiment" to
test an idea is more important than the basic Foucault pendulum itself so you
get two exhibits in one.

Of course, another question is how fast does it decay? Or rather, how long
will it run with no energy input?

This says 2 hours:
http://www.cmnh.org/site/AtTheMuseum/OnExhibit/PermanentExhibits/Foucault.as
px
for a 270 lb bob, but I don't know how tall that is. (But it says 6.2
seconds, so I should be able to calculate it.)
--
These are my opinions, not necessarily my employer's. I hate spam.
Don Latham
2010-07-22 02:10:34 UTC
Permalink
Griffith Park in LA operates a Foucault pendulum that's been going for at
least 70 years (don't ask how I know). They might have a writeup
somewhere. I think te pivot was a simple clamp holding the piano wire.
You'd think it would fail from stress, but the pendulum is very long, so
the angle of the swing is very small. I think the drive actually was done
close to the pivot via a magnet on the wire rather than at the bottom. To
start the pendulum off, a string was tied to hold the pendulum "cocked"
and the string simply burned with a match. A perfect no-torque start...
A simple optical interruptor driving something like a basic stamp and a
ring electromagnet with a PM on the support wire will allow proper timing.
You will be surprised at how little energy is required to keep it going;
it can be roughly calculated from the ball diameter. The beauty of this
system is that the exact frequency of the pendulum is not important. First
order temperature correction can be done in the microprocessor.
Send some pix when you get it going...
Don Latham.

Hal Murray
Post by Hal Murray
... Foucault pendulum ...
Has anyone here had any experience with such a system of have any
suggestions regarding the sustaining system? This is an interesting and
challenging project.
Several years ago, I found a web site for a commercial place that made them
for museums. (I forget why I was looking for that sort of stuff.) You might
find interesting stuff/ideas via google but I didn't find a similar site with
a bit of searching.
----------
Put a magnet on the bottom of the pendulum.
Put a coil below it. (obviously centered)
Use the coil as a sensor to measure the timing.
Use the coil as a motor to pull the pendulum every N-th swing.
The question is how accurately centered do the magnet and coil have to be?
I
don't know. It sounds like a fun mixture of theory and engineering.
One of the variables is how far away is the pendulum when you are pulling.
The farther away it is, the smaller angle you have from the ideal. You can
change that by varying the start/stop times on the pull pulse.
I'd probably put the coil on a crude X-Y table, set it up as good as I could,
then see if it worked. Then I would deliberately move it off a bit and see
what happened. Or try to servo it to the best place, probably by manual
changes every day or week or ???
I'm assuming this is for a school or museum. The required positional
accuracy is actually a real science experiment. The idea of "experiment" to
test an idea is more important than the basic Foucault pendulum itself so you
get two exhibits in one.
Of course, another question is how fast does it decay? Or rather, how long
will it run with no energy input?
http://www.cmnh.org/site/AtTheMuseum/OnExhibit/PermanentExhibits/Foucault.as
px
for a 270 lb bob, but I don't know how tall that is. (But it says 6.2
seconds, so I should be able to calculate it.)
--
These are my opinions, not necessarily my employer's. I hate spam.
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"Neither the voice of authority nor the weight of reason and argument are
as significant as experiment, for thence comes quiet to the mind."
R. Bacon


Dr. Don Latham AJ7LL
Six Mile Systems LLP
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VOX 406-626-4304
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www.sixmilesystems.com
Richard (Rick) Karlquist
2010-07-22 02:13:36 UTC
Permalink
Post by Hal Murray
Several years ago, I found a web site for a commercial place that made them
for museums. (I forget why I was looking for that sort of stuff.) You might
find interesting stuff/ideas via google but I didn't find a similar site with
a bit of searching.
The Museum of Science and Industry in Chicago had one when I lived
there in the 1960's.

Rick N6RK
Randy Scott
2010-07-22 02:21:19 UTC
Permalink
Post by Richard (Rick) Karlquist
The Museum of Science and Industry in Chicago had one when
I lived there in the 1960's.
You lived at the Museum of Science and Industry? :)

Sorry, couldn't resist. But, you actually can live there for a month:

http://www.msichicago.org/matm/

Randy.
Bob Bownes
2010-07-22 02:26:44 UTC
Permalink
There is at least one in DC, at the Smithsonian iirc.

RPI, where I went to college, had one in the 3 story stairwell in the
library. Don't know if it is still there.

I remember one someplace in London too.

Someone mentioned temperature compensation. What would you need to
compensate for? Temp change in the wire wouldn't effect the rotation
as far as I can tell. Swing length might be different based on temp of
the wire I guess, but with a long pendulum, I think the magnet is
going to way overcome that issue.

The one @ RPI had issues due to air movement in the shaft, but that's
a different problem.

I suppose the right method is to use a GPS disciplined oscillator and
the appropriate divider to drive the magnet under the floor. :) To cut
down in draft induced drift and jitter, you'd have to put the whole
thing in a vacuum though!



On Wed, Jul 21, 2010 at 10:13 PM, Richard (Rick) Karlquist
Post by Richard (Rick) Karlquist
Post by Hal Murray
Several years ago, I found a web site for a commercial place that made
them for museums.  (I forget why I was looking for that sort of stuff.)  You
might find interesting stuff/ideas via google but I didn't find a similar
site with a bit of searching.
The Museum of Science and Industry in Chicago had one when I lived
there in the 1960's.
Rick N6RK
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Bob Bownes
2010-07-22 02:40:48 UTC
Permalink
Silly me, I just realized you need to compensate for the change in
length with temperature.

This sounds like a great project!
Post by Bob Bownes
There is at least one in DC, at the Smithsonian iirc.
RPI, where I went to college, had one in the 3 story stairwell in the
library. Don't know if it is still there.
I remember one someplace in London too.
Someone mentioned temperature compensation. What would you need to
compensate for? Temp change in the wire wouldn't effect the rotation
as far as I can tell. Swing length might be different based on temp of
the wire I guess, but with a long pendulum, I think the magnet is
going to way overcome that issue.
a different problem.
I suppose the right method is to use a GPS disciplined oscillator and
the appropriate divider to drive the magnet under the floor. :) To cut
down in draft induced drift and jitter, you'd have to put the whole
thing in a vacuum though!
On Wed, Jul 21, 2010 at 10:13 PM, Richard (Rick) Karlquist
Post by Richard (Rick) Karlquist
Post by Hal Murray
Several years ago, I found a web site for a commercial place that made
them for museums.  (I forget why I was looking for that sort of stuff.)  You
might find interesting stuff/ideas via google but I didn't find a similar
site with a bit of searching.
The Museum of Science and Industry in Chicago had one when I lived
there in the 1960's.
Rick N6RK
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Eugen Leitl
2010-07-22 14:04:36 UTC
Permalink
Post by Bob Bownes
Silly me, I just realized you need to compensate for the change in
length with temperature.
You could use an Invar wire.
Post by Bob Bownes
This sounds like a great project!
Post by Bob Bownes
There is at least one in DC, at the Smithsonian iirc.
RPI, where I went to college, had one in the 3 story stairwell in the
library. Don't know if it is still there.
I remember one someplace in London too.
Someone mentioned temperature compensation. What would you need to
compensate for? Temp change in the wire wouldn't effect the rotation
as far as I can tell. Swing length might be different based on temp of
the wire I guess, but with a long pendulum, I think the magnet is
going to way overcome that issue.
a different problem.
I suppose the right method is to use a GPS disciplined oscillator and
the appropriate divider to drive the magnet under the floor. :) To cut
down in draft induced drift and jitter, you'd have to put the whole
thing in a vacuum though!
On Wed, Jul 21, 2010 at 10:13 PM, Richard (Rick) Karlquist
Post by Richard (Rick) Karlquist
Post by Hal Murray
Several years ago, I found a web site for a commercial place that made
them for museums.  (I forget why I was looking for that sort of stuff.)  You
might find interesting stuff/ideas via google but I didn't find a similar
site with a bit of searching.
The Museum of Science and Industry in Chicago had one when I lived
there in the 1960's.
Rick N6RK
_______________________________________________
To unsubscribe, go to
https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
and follow the instructions there.
_______________________________________________
To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
and follow the instructions there.
--
Eugen* Leitl <a href="http://leitl.org">leitl</a> http://leitl.org
______________________________________________________________
ICBM: 48.07100, 11.36820 http://www.ativel.com http://postbiota.org
8B29F6BE: 099D 78BA 2FD3 B014 B08A 7779 75B0 2443 8B29 F6BE
jimlux
2010-07-22 14:55:38 UTC
Permalink
Post by Eugen Leitl
Post by Bob Bownes
Silly me, I just realized you need to compensate for the change in
length with temperature.
You could use an Invar wire.
Some insight from a friend (a proto-timenut) who was thinking about
building a 1ppm free pendulum in air for a fancy grandfather clock.

Invar (aside from being expensive) isn't appropriate here, depending on
the design. Its low CTE properties depend on not being mechanically
stressed.

A better scheme is the traditional bimetal pendulum compensation
approach of steel rod and brass bob that can slide along the rod. You
pick the dimensions so that as the steel gets longer, the bob expands at
a different rate (pushing the CG back up), so that the net movement in
CG position is zero. You change the relative diameters of the two metal
parts to get the CTEs and movement to balance out.
J. Forster
2010-07-22 02:57:33 UTC
Permalink
Post by Bob Bownes
I remember one someplace in London too.
Science Museum in South Kensington, I'd expect, but I've not been there
20+ years.

-John
Post by Bob Bownes
Someone mentioned temperature compensation. What would you need to
compensate for? Temp change in the wire wouldn't effect the rotation
as far as I can tell. Swing length might be different based on temp of
the wire I guess, but with a long pendulum, I think the magnet is
going to way overcome that issue.
a different problem.
I suppose the right method is to use a GPS disciplined oscillator and
the appropriate divider to drive the magnet under the floor. :) To cut
down in draft induced drift and jitter, you'd have to put the whole
thing in a vacuum though!
You don't want to drive it from a clock, IMO. You want to make it a
free-running oscillator. Period is irrelevant.

-John

==============
David Martindale
2010-07-22 14:06:44 UTC
Permalink
Post by J. Forster
Post by Bob Bownes
I remember one someplace in London too.
Science Museum in South Kensington, I'd expect, but I've not been there
20+ years.
Yes, they have one in one of their open multi-storey stairwells. If I
remember correctly, the energy input is provided by lifting and lowering the
pivot point slightly in sync with the swing, rather than anything done at
the bob end.

Dave
Matthew Kaufman
2010-07-22 14:29:34 UTC
Permalink
http://www.astro.louisville.edu/foucault/pendulum.pdf is one of the best
references I have in my bookmarks.

Matthew Kaufman
Donald Henderickx
2010-07-22 02:02:54 UTC
Permalink
Post by Morris Odell
Hi all,
I have been asked to help with the construction of a Foucault pendulum. This
is a long pendulum which oscillates in a slow stately fashion in a fixed
plane which appears to move as the earth rotates. In reality the surrounding
environment is really moving relative to the plane of oscillation.
The pendulum requires a sustaining system to compensate for the inevitable
energy loss with each swing. The system is located in the building and
therefore rotates relative to the pendulum. It needs to provide an impulse
which does not affect the plane of oscillation of the pendulum. I was
thinking of an electromagnet located below the centre of the swing which
would be pulsed appropriately as the bob passes over it.
Has anyone here had any experience with such a system of have any
suggestions regarding the sustaining system? This is an interesting and
challenging project.
Cheers,
Morris
_______________________________________________
To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
and follow the instructions there.
Hello Morris:
You might contact Fermi National Accelerator Lab in Batavia Illinois at
www.fnal.gov .
There Foucault pendulum is sixteen stories from the suspension point to
the atrium floor,it's impulse device is buried in the sand under the bob.
They may even have a picture of it on there web site.
Try the public information office they should be able to get in contact
with the people that maintain it.
If you are unable to get any help let me know as I might have some
contacts there that would help.
Good Luck
Don Henderickx
mike cook
2010-07-22 19:26:42 UTC
Permalink
As a number of examples have been referenced in the reply to the
original post, I will add a note on one of pendulums that Foucault
himself constructed.
Foucaults original experiments used shortish cables, but Napoleon
wanted a more prestigeous affaire. It was originally installed by
Foucault in the Panthéon in Paris in 1851, but was moved from there in
1855 to the Musée des Arts et Métiers where it has been ever since. In
the doc I found it appears that the original cable has been used since
then.

The sphere :

* steel, brass, lead .
* diameter = 18 cm.
* mass = 28 Kg.

The wire :

* steel.
* lenght = 18 m
* has used since 1855.

The oscillation period of the Foucault's pendulum of the museum is 8,5 s
and is apparent complete rotation occurs in 31,78 h = 31h 47 min at the
latitude 48° 50 '.


Unfortunately the cable reached its sell by date on the 18th May this
year when it broke, dropping the ball on the marble floor , denting it.
Most unfortunate.
Post by Donald Henderickx
Post by Morris Odell
Hi all,
I have been asked to help with the construction of a Foucault
pendulum. This
is a long pendulum which oscillates in a slow stately fashion in a fixed
plane which appears to move as the earth rotates. In reality the surrounding
environment is really moving relative to the plane of oscillation.
The pendulum requires a sustaining system to compensate for the inevitable
energy loss with each swing. The system is located in the building and
therefore rotates relative to the pendulum. It needs to provide an impulse
which does not affect the plane of oscillation of the pendulum. I was
thinking of an electromagnet located below the centre of the swing which
would be pulsed appropriately as the bob passes over it.
Has anyone here had any experience with such a system of have any
suggestions regarding the sustaining system? This is an interesting and
challenging project.
Cheers,
Morris
_______________________________________________
To unsubscribe, go to
https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
and follow the instructions there.
You might contact Fermi National Accelerator Lab in Batavia Illinois
at www.fnal.gov .
There Foucault pendulum is sixteen stories from the suspension point
to the atrium floor,it's impulse device is buried in the sand under
the bob.
They may even have a picture of it on there web site.
Try the public information office they should be able to get in
contact with the people that maintain it.
If you are unable to get any help let me know as I might have some
contacts there that would help.
Good Luck
Don Henderickx
_______________________________________________
To unsubscribe, go to
https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
and follow the instructions there.
Bob Bownes
2010-07-22 19:29:24 UTC
Permalink
 Unfortunately the cable reached its sell by date on the 18th May this year
when it broke, dropping the ball on the marble floor , denting it. Most
unfortunate.
Denting the bob or the marble floor? :)
mike cook
2010-07-22 19:44:11 UTC
Permalink
I thought that might have caused some confusion ;) . The bob, of course.
I guess it can be replaced, but it is a shame that as a historical
instrument, it could not have been better cared for. All is not lost
though, as one of his smaller original pendulums is swinging in the
Panthéon it seems.
Post by Bob Bownes
Unfortunately the cable reached its sell by date on the 18th May this year
when it broke, dropping the ball on the marble floor , denting it. Most
unfortunate.
Denting the bob or the marble floor? :)
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Bob Camp
2010-07-22 20:03:30 UTC
Permalink
Hi

I assume that was Napoleon III rather than the original....

(I'd hate to see the time-nuts list get banned by the French History
Police).

Bob

-----Original Message-----
From: time-nuts-bounces-***@public.gmane.org [mailto:time-nuts-bounces-***@public.gmane.org] On
Behalf Of mike cook
Sent: Thursday, July 22, 2010 3:27 PM
To: time-nuts-***@public.gmane.org
Subject: Re: [time-nuts] A different timenuts interest

As a number of examples have been referenced in the reply to the
original post, I will add a note on one of pendulums that Foucault
himself constructed.
Foucaults original experiments used shortish cables, but Napoleon
wanted a more prestigeous affaire. It was originally installed by
Foucault in the Panthéon in Paris in 1851, but was moved from there in
1855 to the Musée des Arts et Métiers where it has been ever since. In
the doc I found it appears that the original cable has been used since
then.

The sphere :

* steel, brass, lead .
* diameter = 18 cm.
* mass = 28 Kg.

The wire :

* steel.
* lenght = 18 m
* has used since 1855.

The oscillation period of the Foucault's pendulum of the museum is 8,5 s
and is apparent complete rotation occurs in 31,78 h = 31h 47 min at the
latitude 48° 50 '.


Unfortunately the cable reached its sell by date on the 18th May this
year when it broke, dropping the ball on the marble floor , denting it.
Most unfortunate.
Post by Donald Henderickx
Post by Morris Odell
Hi all,
I have been asked to help with the construction of a Foucault
pendulum. This
is a long pendulum which oscillates in a slow stately fashion in a fixed
plane which appears to move as the earth rotates. In reality the surrounding
environment is really moving relative to the plane of oscillation.
The pendulum requires a sustaining system to compensate for the inevitable
energy loss with each swing. The system is located in the building and
therefore rotates relative to the pendulum. It needs to provide an impulse
which does not affect the plane of oscillation of the pendulum. I was
thinking of an electromagnet located below the centre of the swing which
would be pulsed appropriately as the bob passes over it.
Has anyone here had any experience with such a system of have any
suggestions regarding the sustaining system? This is an interesting and
challenging project.
Cheers,
Morris
_______________________________________________
To unsubscribe, go to
https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
and follow the instructions there.
You might contact Fermi National Accelerator Lab in Batavia Illinois
at www.fnal.gov .
There Foucault pendulum is sixteen stories from the suspension point
to the atrium floor,it's impulse device is buried in the sand under
the bob.
They may even have a picture of it on there web site.
Try the public information office they should be able to get in
contact with the people that maintain it.
If you are unable to get any help let me know as I might have some
contacts there that would help.
Good Luck
Don Henderickx
_______________________________________________
To unsubscribe, go to
https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
and follow the instructions there.
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Jean-Louis Oneto
2010-07-22 23:11:15 UTC
Permalink
I also think so,
but Time-nuts are nuts about attoseconds, not decades... ;-}
Jean-Louis Oneto

----- Original Message -----
From: "Bob Camp" <lists-***@public.gmane.org>
To: "'Discussion of precise time and frequency measurement'"
<time-nuts-***@public.gmane.org>
Sent: Thursday, July 22, 2010 8:03 PM
Subject: Re: [time-nuts] A different timenuts interest
Post by Bob Camp
Hi
I assume that was Napoleon III rather than the original....
(I'd hate to see the time-nuts list get banned by the French History
Police).
Bob
-----Original Message-----
Behalf Of mike cook
Sent: Thursday, July 22, 2010 3:27 PM
Subject: Re: [time-nuts] A different timenuts interest
As a number of examples have been referenced in the reply to the
original post, I will add a note on one of pendulums that Foucault
himself constructed.
Foucaults original experiments used shortish cables, but Napoleon
wanted a more prestigeous affaire. It was originally installed by
Foucault in the Panthéon in Paris in 1851, but was moved from there in
1855 to the Musée des Arts et Métiers where it has been ever since. In
the doc I found it appears that the original cable has been used since
then.
* steel, brass, lead .
* diameter = 18 cm.
* mass = 28 Kg.
* steel.
* lenght = 18 m
* has used since 1855.
The oscillation period of the Foucault's pendulum of the museum is 8,5 s
and is apparent complete rotation occurs in 31,78 h = 31h 47 min at the
latitude 48° 50 '.
Unfortunately the cable reached its sell by date on the 18th May this
year when it broke, dropping the ball on the marble floor , denting it.
Most unfortunate.
Post by Donald Henderickx
Post by Morris Odell
Hi all,
I have been asked to help with the construction of a Foucault
pendulum. This
is a long pendulum which oscillates in a slow stately fashion in a fixed
plane which appears to move as the earth rotates. In reality the surrounding
environment is really moving relative to the plane of oscillation.
The pendulum requires a sustaining system to compensate for the inevitable
energy loss with each swing. The system is located in the building and
therefore rotates relative to the pendulum. It needs to provide an impulse
which does not affect the plane of oscillation of the pendulum. I was
thinking of an electromagnet located below the centre of the swing which
would be pulsed appropriately as the bob passes over it.
Has anyone here had any experience with such a system of have any
suggestions regarding the sustaining system? This is an interesting and
challenging project.
Cheers,
Morris
_______________________________________________
To unsubscribe, go to
https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
and follow the instructions there.
You might contact Fermi National Accelerator Lab in Batavia Illinois
at www.fnal.gov .
There Foucault pendulum is sixteen stories from the suspension point
to the atrium floor,it's impulse device is buried in the sand under
the bob.
They may even have a picture of it on there web site.
Try the public information office they should be able to get in
contact with the people that maintain it.
If you are unable to get any help let me know as I might have some
contacts there that would help.
Good Luck
Don Henderickx
_______________________________________________
To unsubscribe, go to
https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
and follow the instructions there.
_______________________________________________
To unsubscribe, go to
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and follow the instructions there.
_______________________________________________
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jmfranke
2010-07-22 23:24:28 UTC
Permalink
Actually, I think you can find a time-nut for any span of time,
sub-nanosecond to leap seconds, to leap years, to ...

John WA4WDL

--------------------------------------------------
From: "Jean-Louis Oneto" <Jean-Louis.Oneto-***@public.gmane.org>
Sent: Thursday, July 22, 2010 7:11 PM
To: "Discussion of precise time and frequency measurement"
<time-nuts-***@public.gmane.org>
Subject: Re: [time-nuts] A different timenuts interest
Post by Jean-Louis Oneto
I also think so,
but Time-nuts are nuts about attoseconds, not decades... ;-}
Jean-Louis Oneto
----- Original Message -----
To: "'Discussion of precise time and frequency measurement'"
Sent: Thursday, July 22, 2010 8:03 PM
Subject: Re: [time-nuts] A different timenuts interest
Post by Bob Camp
Hi
I assume that was Napoleon III rather than the original....
(I'd hate to see the time-nuts list get banned by the French History
Police).
Bob
-----Original Message-----
Behalf Of mike cook
Sent: Thursday, July 22, 2010 3:27 PM
Subject: Re: [time-nuts] A different timenuts interest
As a number of examples have been referenced in the reply to the
original post, I will add a note on one of pendulums that Foucault
himself constructed.
Foucaults original experiments used shortish cables, but Napoleon
wanted a more prestigeous affaire. It was originally installed by
Foucault in the Panthéon in Paris in 1851, but was moved from there in
1855 to the Musée des Arts et Métiers where it has been ever since. In
the doc I found it appears that the original cable has been used since
then.
* steel, brass, lead .
* diameter = 18 cm.
* mass = 28 Kg.
* steel.
* lenght = 18 m
* has used since 1855.
The oscillation period of the Foucault's pendulum of the museum is 8,5 s
and is apparent complete rotation occurs in 31,78 h = 31h 47 min at the
latitude 48° 50 '.
Unfortunately the cable reached its sell by date on the 18th May this
year when it broke, dropping the ball on the marble floor , denting it.
Most unfortunate.
Post by Donald Henderickx
Post by Morris Odell
Hi all,
I have been asked to help with the construction of a Foucault
pendulum. This
is a long pendulum which oscillates in a slow stately fashion in a fixed
plane which appears to move as the earth rotates. In reality the surrounding
environment is really moving relative to the plane of oscillation.
The pendulum requires a sustaining system to compensate for the inevitable
energy loss with each swing. The system is located in the building and
therefore rotates relative to the pendulum. It needs to provide an impulse
which does not affect the plane of oscillation of the pendulum. I was
thinking of an electromagnet located below the centre of the swing which
would be pulsed appropriately as the bob passes over it.
Has anyone here had any experience with such a system of have any
suggestions regarding the sustaining system? This is an interesting and
challenging project.
Cheers,
Morris
_______________________________________________
To unsubscribe, go to
https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
and follow the instructions there.
You might contact Fermi National Accelerator Lab in Batavia Illinois
at www.fnal.gov .
There Foucault pendulum is sixteen stories from the suspension point
to the atrium floor,it's impulse device is buried in the sand under
the bob.
They may even have a picture of it on there web site.
Try the public information office they should be able to get in
contact with the people that maintain it.
If you are unable to get any help let me know as I might have some
contacts there that would help.
Good Luck
Don Henderickx
_______________________________________________
To unsubscribe, go to
https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
and follow the instructions there.
_______________________________________________
To unsubscribe, go to
https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
and follow the instructions there.
_______________________________________________
To unsubscribe, go to
https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
and follow the instructions there.
_______________________________________________
To unsubscribe, go to
https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
and follow the instructions there.
Oz-in-DFW
2010-07-22 23:54:29 UTC
Permalink
Hmmm. I thought time-nuts were nuts about time, with branch interests
in accuracy, resolution, history...
Post by jmfranke
Actually, I think you can find a time-nut for any span of time,
sub-nanosecond to leap seconds, to leap years, to ...
John WA4WDL
--------------------------------------------------
Sent: Thursday, July 22, 2010 7:11 PM
To: "Discussion of precise time and frequency measurement"
Subject: Re: [time-nuts] A different timenuts interest
Post by Jean-Louis Oneto
I also think so,
but Time-nuts are nuts about attoseconds, not decades... ;-}
Jean-Louis Oneto
To: "'Discussion of precise time and frequency measurement'"
Sent: Thursday, July 22, 2010 8:03 PM
Subject: Re: [time-nuts] A different timenuts interest
Post by Bob Camp
Hi
I assume that was Napoleon III rather than the original....
(I'd hate to see the time-nuts list get banned by the French History
Police).
Bob
--
mailto:oz-***@public.gmane.org
Oz
POB 93167
Southlake, TX 76092 (Near DFW Airport)
Magnus Danielson
2010-07-23 00:11:04 UTC
Permalink
Post by Oz-in-DFW
Hmmm. I thought time-nuts were nuts about time, with branch interests
in accuracy, resolution, history...
History is nanoseconds ago.
Recent history is picoseconds ago.
Just now is femtoseconds ago.
Fraction of mind ago is attoseconds ago.
Acient history is microseconds ago.
Ages is microseconds ago
Major epochs in time i seconds ago.
Geological short period is minutes ago.
Geological epoch period is hours ago.

No?

Cheers,
Magnus
Post by Oz-in-DFW
Post by jmfranke
Actually, I think you can find a time-nut for any span of time,
sub-nanosecond to leap seconds, to leap years, to ...
John WA4WDL
--------------------------------------------------
Sent: Thursday, July 22, 2010 7:11 PM
To: "Discussion of precise time and frequency measurement"
Subject: Re: [time-nuts] A different timenuts interest
Post by Jean-Louis Oneto
I also think so,
but Time-nuts are nuts about attoseconds, not decades... ;-}
Jean-Louis Oneto
To: "'Discussion of precise time and frequency measurement'"
Sent: Thursday, July 22, 2010 8:03 PM
Subject: Re: [time-nuts] A different timenuts interest
Post by Bob Camp
Hi
I assume that was Napoleon III rather than the original....
(I'd hate to see the time-nuts list get banned by the French History
Police).
Bob
Matthew Kaufman
2010-07-23 00:15:42 UTC
Permalink
Post by Magnus Danielson
Post by Oz-in-DFW
Hmmm. I thought time-nuts were nuts about time, with branch interests
in accuracy, resolution, history...
History is nanoseconds ago.
Recent history is picoseconds ago.
Just now is femtoseconds ago.
Fraction of mind ago is attoseconds ago.
Acient history is microseconds ago.
Ages is microseconds ago
Major epochs in time i seconds ago.
Geological short period is minutes ago.
Geological epoch period is hours ago.
No?
Neurons just don't work that fast. "Just now" is still milliseconds, and
then there's all the time-reordering that happens in your brain to make
the skew make sense...

Matthew Kaufman
Magnus Danielson
2010-07-23 01:06:04 UTC
Permalink
Matthew,
Post by Matthew Kaufman
Post by Magnus Danielson
Hmmm. I thought time-nuts were nuts about time, with branch interests
in accuracy, resolution, history...
History is nanoseconds ago.
Recent history is picoseconds ago.
Just now is femtoseconds ago.
Fraction of mind ago is attoseconds ago.
Acient history is microseconds ago.
Ages is microseconds ago
Major epochs in time i seconds ago.
Geological short period is minutes ago.
Geological epoch period is hours ago.
No?
Neurons just don't work that fast. "Just now" is still milliseconds, and
then there's all the time-reordering that happens in your brain to make
the skew make sense...
It was meant as a joke...

When working on modern digital electronics and multi-gigabit links
time-scales becomes somewhat shifted and 1 ms becomes a minor eternity.

Cheers,
Magnus
J. Forster
2010-07-23 02:05:30 UTC
Permalink
Errrr.... A Foucalt Pendulum is not about time! It's about motion in
inertial space.

-John

===============
Post by Magnus Danielson
Matthew,
Post by Matthew Kaufman
Post by Magnus Danielson
Hmmm. I thought time-nuts were nuts about time, with branch interests
in accuracy, resolution, history...
History is nanoseconds ago.
Recent history is picoseconds ago.
Just now is femtoseconds ago.
Fraction of mind ago is attoseconds ago.
Acient history is microseconds ago.
Ages is microseconds ago
Major epochs in time i seconds ago.
Geological short period is minutes ago.
Geological epoch period is hours ago.
No?
Neurons just don't work that fast. "Just now" is still milliseconds, and
then there's all the time-reordering that happens in your brain to make
the skew make sense...
It was meant as a joke...
When working on modern digital electronics and multi-gigabit links
time-scales becomes somewhat shifted and 1 ms becomes a minor eternity.
Cheers,
Magnus
_______________________________________________
To unsubscribe, go to
https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
and follow the instructions there.
jimlux
2010-07-23 02:30:19 UTC
Permalink
Post by J. Forster
Errrr.... A Foucalt Pendulum is not about time! It's about motion in
inertial space.
are they not the same, underneath it all?
Bill Hawkins
2010-07-22 02:31:33 UTC
Permalink
Well, Morris, this does sound interesting.

You've had some pretty conventional replies, so let's up the ante a bit.

If you need to know where something macroscopic is in space, attach a GPS
receiver to it. Then program some PIC device (lots of advice about that on
this list) to compute optimum impulse points after calculating an error that
can be corrected by the minimum possible impulse.

NASA could advise you about small impulse rocket systems. They may even have
a few Space Shuttle micro thrusters and fuel systems for sale. You may be
able to drop fuel and oxidizer into the tanks at certain positions of the
bob.

The bob on a Foucault pendulum is usually quite massive, so there's no
reason
why it can't be inexpensive lead-acid batteries that are recharged by solar
cells.

I'm sure you'd save money over mechanisms to move the pivot or huge magnets
buried in the floor.

Given present unemployment levels, you may be able to hire a person to
deliver
impulses to the bob as required. But most of the world has automated such
systems because people are not reliable.

Heck, you could build a pendulum and a metaphor for our times.

Best regards,
Bill Hawkins (also on Jack's BA list)


-----Original Message-----
From: time-nuts-bounces-***@public.gmane.org [mailto:time-nuts-bounces-***@public.gmane.org] On
Behalf Of Morris Odell
Sent: Wednesday, July 21, 2010 7:13 PM
To: time-nuts-***@public.gmane.org
Subject: [time-nuts] A different timenuts interest

Hi all,

I have been asked to help with the construction of a Foucault pendulum. This
is a long pendulum which oscillates in a slow stately fashion in a fixed
plane which appears to move as the earth rotates. In reality the surrounding
environment is really moving relative to the plane of oscillation.

The pendulum requires a sustaining system to compensate for the inevitable
energy loss with each swing. The system is located in the building and
therefore rotates relative to the pendulum. It needs to provide an impulse
which does not affect the plane of oscillation of the pendulum. I was
thinking of an electromagnet located below the centre of the swing which
would be pulsed appropriately as the bob passes over it.

Has anyone here had any experience with such a system of have any
suggestions regarding the sustaining system? This is an interesting and
challenging project.

Cheers,

Morris
J. Forster
2010-07-22 03:05:06 UTC
Permalink
[snip]
Post by Bill Hawkins
The bob on a Foucault pendulum is usually quite massive, so there's no
reason
why it can't be inexpensive lead-acid batteries that are recharged by
solar cells.
IMO, there is no reason to put anything active on the bob.
Post by Bill Hawkins
I'm sure you'd save money over mechanisms to move the pivot or huge
magnets buried in the floor.
The pendulum is very high "Q". You don't want or need a lot of force. I'd
guess a coil smaller than a coffee cup would be more than enough.
Post by Bill Hawkins
Given present unemployment levels, you may be able to hire a person to
deliver
impulses to the bob as required. But most of the world has automated such
systems because people are not reliable.
True. When in China in about 1979, I was astounded they had Elevator
Operators. Many of them, but they had more people than jobs.
Post by Bill Hawkins
Heck, you could build a pendulum and a metaphor for our times.
Best regards,
Bill Hawkins (also on Jack's BA list)
Best,

-John

================
Hal Murray
2010-07-22 02:51:38 UTC
Permalink
Silly me, I just realized you need to compensate for the change in length
with temperature.
It depends...

If your setup to replace the energy is PLLed to the pendulum position it
doesn't need to know the period. (at least not very accurately)
--
These are my opinions, not necessarily my employer's. I hate spam.
jimlux
2010-07-22 03:57:10 UTC
Permalink
Post by Morris Odell
Hi all,
I have been asked to help with the construction of a Foucault pendulum. This
is a long pendulum which oscillates in a slow stately fashion in a fixed
plane which appears to move as the earth rotates. In reality the surrounding
environment is really moving relative to the plane of oscillation.
The pendulum requires a sustaining system to compensate for the inevitable
energy loss with each swing. The system is located in the building and
therefore rotates relative to the pendulum. It needs to provide an impulse
which does not affect the plane of oscillation of the pendulum. I was
thinking of an electromagnet located below the centre of the swing which
would be pulsed appropriately as the bob passes over it.
Has anyone here had any experience with such a system of have any
suggestions regarding the sustaining system? This is an interesting and
challenging project.
Google should be your friend. This is a pretty standard thing, and I
recall seeing drawings of optical schemes with phototubes to detect when
the wire passes through vertical (and triggering the pulse through the
electromagnet below the bob).
Kasper Pedersen
2010-07-22 08:06:23 UTC
Permalink
Post by Morris Odell
The pendulum requires a sustaining system to compensate for the inevitable
energy loss with each swing. The system is located in the building and
therefore rotates relative to the pendulum. It needs to provide an impulse
which does not affect the plane of oscillation of the pendulum. I was
thinking of an electromagnet located below the centre of the swing which
would be pulsed appropriately as the bob passes over it.
As a kid, I did a self sustaining pendulum with no moving parts and no
magnets:

The bob was suspended by two parallel wires, lacquered together, and
shorted at the bob end. As the bob passed over the center, a one-shot
sent a good-sized current pulse through the wire, heating it, making it
slightly longer, and then shrink again as it cooled at the outside of
the swing.

For a heavy pendulum, and thick wire, the time constant in the cooling
phase will likely make this infeasible.

/Kasper Pedersen
Flemming Larsen
2010-07-22 08:47:23 UTC
Permalink
The Exploratorium at The Palace of Fine Arts in San Francisco had one of these, and
may still have it. I haven't been there in a while and don't know the details.
 
Nuts & Volts had a construction project for a continuously swinging pendulum in their
September 2009 issue. It had a magnet at the end of the pendulum which generated
a current in a coil mounted in the center of the base. A simple 2-transistor circuit would
sense the pendulum swing and would generate a pulse in the same coil to accelerate
the pendulum and keep it swinging in infinity, or until the battery died, whichever came
first.
 
Have you looked for ideas on Bryan Mumford's website?
 
-- FL

 

--- Den ons 21/7/10 skrev Morris Odell <vilgotch-bzGI/***@public.gmane.org>:


Fra: Morris Odell <vilgotch-bzGI/***@public.gmane.org>
Emne: [time-nuts] A different timenuts interest
Til: time-nuts-***@public.gmane.org
Dato: onsdag 21. juli 2010 17.13


Hi all,

I have been asked to help with the construction of a Foucault pendulum. This
is a long pendulum which oscillates in a slow stately fashion in a fixed
plane which appears to move as the earth rotates. In reality the surrounding
environment is really moving relative to the plane of oscillation.

The pendulum requires a sustaining system to compensate for the inevitable
energy loss with each swing. The system is located in the building and
therefore rotates relative to the pendulum. It needs to provide an impulse
which does not affect the plane of oscillation of the pendulum. I was
thinking of an electromagnet located below the centre of the swing which
would be pulsed appropriately as the bob passes over it.

Has anyone here had any experience with such a system of have any
suggestions regarding the sustaining system? This is an interesting and
challenging project.

Cheers,

Morris



_______________________________________________
time-nuts mailing list -- time-nuts-***@public.gmane.org
To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
and follow the instructions there.
Brooke Clarke
2010-07-22 14:37:35 UTC
Permalink
Hi Morris:

See:
http://www.calacademy.org/products/pendulum/pendulum_sales.html
http://www.calacademy.org/products/pendulum/pendspec.pdf
they are not cheap, but a proven design and probably lower in cost than
making just one of them.

One of these was working at Foothill College in Los Altos Hills,
California when I was there. It was outside in a combined pit and
tower, but is not longer in use. It needs to be somewhere inside where
vandals can not get to it.

Have Fun,

Brooke Clarke
http://www.PRC68.com
Post by Morris Odell
Hi all,
I have been asked to help with the construction of a Foucault pendulum. This
is a long pendulum which oscillates in a slow stately fashion in a fixed
plane which appears to move as the earth rotates. In reality the surrounding
environment is really moving relative to the plane of oscillation.
The pendulum requires a sustaining system to compensate for the inevitable
energy loss with each swing. The system is located in the building and
therefore rotates relative to the pendulum. It needs to provide an impulse
which does not affect the plane of oscillation of the pendulum. I was
thinking of an electromagnet located below the centre of the swing which
would be pulsed appropriately as the bob passes over it.
Has anyone here had any experience with such a system of have any
suggestions regarding the sustaining system? This is an interesting and
challenging project.
Cheers,
Morris
_______________________________________________
To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
and follow the instructions there.
Bob Camp
2010-07-22 16:52:58 UTC
Permalink
Hi

At > $30K certainly not cheap. My guess is that the building modifications
and permits will set you back a pretty significant chunk of money as well.

The issue of troubleshooting a 6 story high machine in a public space (plus
insurance issues) likely makes the "proven design" a much better decision
than a one off.

Bob

-----Original Message-----
From: time-nuts-bounces-***@public.gmane.org [mailto:time-nuts-bounces-***@public.gmane.org] On
Behalf Of Brooke Clarke
Sent: Thursday, July 22, 2010 10:38 AM
To: Discussion of precise time and frequency measurement
Cc: Morris Odell
Subject: Re: [time-nuts] A different timenuts interest

Hi Morris:

See:
http://www.calacademy.org/products/pendulum/pendulum_sales.html
http://www.calacademy.org/products/pendulum/pendspec.pdf
they are not cheap, but a proven design and probably lower in cost than
making just one of them.

One of these was working at Foothill College in Los Altos Hills,
California when I was there. It was outside in a combined pit and
tower, but is not longer in use. It needs to be somewhere inside where
vandals can not get to it.

Have Fun,

Brooke Clarke
http://www.PRC68.com
Post by Morris Odell
Hi all,
I have been asked to help with the construction of a Foucault pendulum. This
is a long pendulum which oscillates in a slow stately fashion in a fixed
plane which appears to move as the earth rotates. In reality the surrounding
environment is really moving relative to the plane of oscillation.
The pendulum requires a sustaining system to compensate for the inevitable
energy loss with each swing. The system is located in the building and
therefore rotates relative to the pendulum. It needs to provide an impulse
which does not affect the plane of oscillation of the pendulum. I was
thinking of an electromagnet located below the centre of the swing which
would be pulsed appropriately as the bob passes over it.
Has anyone here had any experience with such a system of have any
suggestions regarding the sustaining system? This is an interesting and
challenging project.
Cheers,
Morris
_______________________________________________
To unsubscribe, go to
https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
Post by Morris Odell
and follow the instructions there.
_______________________________________________
time-nuts mailing list -- time-nuts-***@public.gmane.org
To unsubscribe, go to
https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
and follow the instructions there.
Bill Hawkins
2010-07-22 17:26:44 UTC
Permalink
Well, I thought it was interesting that a barrier was needed at least
3 feet away from the swing so that people would not grab the cable.

Can you imagine the effect of grabbing the cable with a 250 pound bob
attached?

I'd build one called "Evolution in Action." Put a Poe-like blade on
the bottom of the ball and omit the railing. That is, if I had the
money, ah, and the building. And my own country, where allowing idiots
to breed was illegal.

Bill Hawkins

-----Original Message-----
From: time-nuts-bounces-***@public.gmane.org [mailto:time-nuts-bounces-***@public.gmane.org] On
Behalf Of Bob Camp
Sent: Thursday, July 22, 2010 11:53 AM
To: 'Discussion of precise time and frequency measurement'
Subject: Re: [time-nuts] A different timenuts interest

Hi

At > $30K certainly not cheap. My guess is that the building modifications
and permits will set you back a pretty significant chunk of money as well.

The issue of troubleshooting a 6 story high machine in a public space (plus
insurance issues) likely makes the "proven design" a much better decision
than a one off.

Bob

-----Original Message-----
From: time-nuts-bounces-***@public.gmane.org [mailto:time-nuts-bounces-***@public.gmane.org] On
Behalf Of Brooke Clarke
Sent: Thursday, July 22, 2010 10:38 AM
To: Discussion of precise time and frequency measurement
Cc: Morris Odell
Subject: Re: [time-nuts] A different timenuts interest

Hi Morris:

See:
http://www.calacademy.org/products/pendulum/pendulum_sales.html
http://www.calacademy.org/products/pendulum/pendspec.pdf
they are not cheap, but a proven design and probably lower in cost than
making just one of them.

One of these was working at Foothill College in Los Altos Hills,
California when I was there. It was outside in a combined pit and
tower, but is not longer in use. It needs to be somewhere inside where
vandals can not get to it.

Have Fun,

Brooke Clarke
http://www.PRC68.com
Post by Morris Odell
Hi all,
I have been asked to help with the construction of a Foucault pendulum. This
is a long pendulum which oscillates in a slow stately fashion in a fixed
plane which appears to move as the earth rotates. In reality the surrounding
environment is really moving relative to the plane of oscillation.
The pendulum requires a sustaining system to compensate for the inevitable
energy loss with each swing. The system is located in the building and
therefore rotates relative to the pendulum. It needs to provide an impulse
which does not affect the plane of oscillation of the pendulum. I was
thinking of an electromagnet located below the centre of the swing which
would be pulsed appropriately as the bob passes over it.
Has anyone here had any experience with such a system of have any
suggestions regarding the sustaining system? This is an interesting and
challenging project.
Cheers,
Morris
_______________________________________________
To unsubscribe, go to
https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
Post by Morris Odell
and follow the instructions there.
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J. Forster
2010-07-22 17:34:22 UTC
Permalink
How about putting a high voltage, high frequency on the bob and wire, so
any body part that gets within say 2 feet draws giant arcs? :<))

-John

===============
Post by Bill Hawkins
Well, I thought it was interesting that a barrier was needed at least
3 feet away from the swing so that people would not grab the cable.
Can you imagine the effect of grabbing the cable with a 250 pound bob
attached?
I'd build one called "Evolution in Action." Put a Poe-like blade on
the bottom of the ball and omit the railing. That is, if I had the
money, ah, and the building. And my own country, where allowing idiots
to breed was illegal.
Bill Hawkins
-----Original Message-----
Behalf Of Bob Camp
Sent: Thursday, July 22, 2010 11:53 AM
To: 'Discussion of precise time and frequency measurement'
Subject: Re: [time-nuts] A different timenuts interest
Hi
At > $30K certainly not cheap. My guess is that the building modifications
and permits will set you back a pretty significant chunk of money as well.
The issue of troubleshooting a 6 story high machine in a public space (plus
insurance issues) likely makes the "proven design" a much better decision
than a one off.
Bob
-----Original Message-----
Behalf Of Brooke Clarke
Sent: Thursday, July 22, 2010 10:38 AM
To: Discussion of precise time and frequency measurement
Cc: Morris Odell
Subject: Re: [time-nuts] A different timenuts interest
http://www.calacademy.org/products/pendulum/pendulum_sales.html
http://www.calacademy.org/products/pendulum/pendspec.pdf
they are not cheap, but a proven design and probably lower in cost than
making just one of them.
One of these was working at Foothill College in Los Altos Hills,
California when I was there. It was outside in a combined pit and
tower, but is not longer in use. It needs to be somewhere inside where
vandals can not get to it.
Have Fun,
Brooke Clarke
http://www.PRC68.com
Post by Morris Odell
Hi all,
I have been asked to help with the construction of a Foucault pendulum.
This
Post by Morris Odell
is a long pendulum which oscillates in a slow stately fashion in a fixed
plane which appears to move as the earth rotates. In reality the
surrounding
Post by Morris Odell
environment is really moving relative to the plane of oscillation.
The pendulum requires a sustaining system to compensate for the inevitable
energy loss with each swing. The system is located in the building and
therefore rotates relative to the pendulum. It needs to provide an impulse
which does not affect the plane of oscillation of the pendulum. I was
thinking of an electromagnet located below the centre of the swing which
would be pulsed appropriately as the bob passes over it.
Has anyone here had any experience with such a system of have any
suggestions regarding the sustaining system? This is an interesting and
challenging project.
Cheers,
Morris
_______________________________________________
To unsubscribe, go to
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Post by Morris Odell
and follow the instructions there.
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Mike Naruta AA8K
2010-07-22 17:44:35 UTC
Permalink
Wouldn't that affect the path of the pendulum
by interacting with the Earth's magnetic field?

:)
Post by J. Forster
How about putting a high voltage, high frequency on the bob and wire, so
any body part that gets within say 2 feet draws giant arcs? :<))
-John
Don Latham
2010-07-22 18:12:49 UTC
Permalink
The Griffith Park exhibit did include a Tesla Coil. Hmmmmm...
Don

J. Forster
Post by J. Forster
How about putting a high voltage, high frequency on the bob and wire, so
any body part that gets within say 2 feet draws giant arcs? :<))
-John
===============
Post by Bill Hawkins
Well, I thought it was interesting that a barrier was needed at least
3 feet away from the swing so that people would not grab the cable.
Can you imagine the effect of grabbing the cable with a 250 pound bob
attached?
I'd build one called "Evolution in Action." Put a Poe-like blade on
the bottom of the ball and omit the railing. That is, if I had the
money, ah, and the building. And my own country, where allowing idiots
to breed was illegal.
Bill Hawkins
-----Original Message-----
Behalf Of Bob Camp
Sent: Thursday, July 22, 2010 11:53 AM
To: 'Discussion of precise time and frequency measurement'
Subject: Re: [time-nuts] A different timenuts interest
Hi
At > $30K certainly not cheap. My guess is that the building
modifications
and permits will set you back a pretty significant chunk of money as well.
The issue of troubleshooting a 6 story high machine in a public space (plus
insurance issues) likely makes the "proven design" a much better decision
than a one off.
Bob
-----Original Message-----
Behalf Of Brooke Clarke
Sent: Thursday, July 22, 2010 10:38 AM
To: Discussion of precise time and frequency measurement
Cc: Morris Odell
Subject: Re: [time-nuts] A different timenuts interest
http://www.calacademy.org/products/pendulum/pendulum_sales.html
http://www.calacademy.org/products/pendulum/pendspec.pdf
they are not cheap, but a proven design and probably lower in cost than
making just one of them.
One of these was working at Foothill College in Los Altos Hills,
California when I was there. It was outside in a combined pit and
tower, but is not longer in use. It needs to be somewhere inside where
vandals can not get to it.
Have Fun,
Brooke Clarke
http://www.PRC68.com
Post by Morris Odell
Hi all,
I have been asked to help with the construction of a Foucault pendulum.
This
Post by Morris Odell
is a long pendulum which oscillates in a slow stately fashion in a fixed
plane which appears to move as the earth rotates. In reality the
surrounding
Post by Morris Odell
environment is really moving relative to the plane of oscillation.
The pendulum requires a sustaining system to compensate for the inevitable
energy loss with each swing. The system is located in the building and
therefore rotates relative to the pendulum. It needs to provide an impulse
which does not affect the plane of oscillation of the pendulum. I was
thinking of an electromagnet located below the centre of the swing which
would be pulsed appropriately as the bob passes over it.
Has anyone here had any experience with such a system of have any
suggestions regarding the sustaining system? This is an interesting and
challenging project.
Cheers,
Morris
_______________________________________________
To unsubscribe, go to
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Post by Morris Odell
and follow the instructions there.
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--
"Neither the voice of authority nor the weight of reason and argument are
as significant as experiment, for thence comes quiet to the mind."
R. Bacon


Dr. Don Latham AJ7LL
Six Mile Systems LLP
17850 Six Mile Road
POB 134
Huson, MT, 59846
VOX 406-626-4304
www.lightningforensics.com
www.sixmilesystems.com
Richard W. Solomon
1970-01-01 00:00:00 UTC
Permalink
IIRC, there was a large one at Weston Observatory (Boston
College). But, it has been 40+ years since I was last there.

73, Dick, W1KSZ


-----Original Message-----
Sent: Jul 22, 2010 1:47 AM
Subject: Re: [time-nuts] A different timenuts interest
The Exploratorium at The Palace of Fine Arts in San Francisco had one of these, and
may still have it. I haven't been there in a while and don't know the details.
 
Nuts & Volts had a construction project for a continuously swinging pendulum in their
September 2009 issue. It had a magnet at the end of the pendulum which generated
a current in a coil mounted in the center of the base. A simple 2-transistor circuit would
sense the pendulum swing and would generate a pulse in the same coil to accelerate
the pendulum and keep it swinging in infinity, or until the battery died, whichever came
first.
 
Have you looked for ideas on Bryan Mumford's website?
 
-- FL
 
Emne: [time-nuts] A different timenuts interest
Dato: onsdag 21. juli 2010 17.13
Hi all,
I have been asked to help with the construction of a Foucault pendulum. This
is a long pendulum which oscillates in a slow stately fashion in a fixed
plane which appears to move as the earth rotates. In reality the surrounding
environment is really moving relative to the plane of oscillation.
The pendulum requires a sustaining system to compensate for the inevitable
energy loss with each swing. The system is located in the building and
therefore rotates relative to the pendulum. It needs to provide an impulse
which does not affect the plane of oscillation of the pendulum. I was
thinking of an electromagnet located below the centre of the swing which
would be pulsed appropriately as the bob passes over it.
Has anyone here had any experience with such a system of have any
suggestions regarding the sustaining system? This is an interesting and
challenging project.
Cheers,
Morris
_______________________________________________
To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
and follow the instructions there.
_______________________________________________
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Hal Murray
2010-07-22 20:18:56 UTC
Permalink
Post by Kasper Pedersen
As a kid, I did a self sustaining pendulum with no moving parts and no
The bob was suspended by two parallel wires, lacquered together, and
shorted at the bob end. As the bob passed over the center, a one-shot sent
a good-sized current pulse through the wire, heating it, making it slightly
longer, and then shrink again as it cooled at the outside of the swing.
Neat. Thanks.
Post by Kasper Pedersen
For a heavy pendulum, and thick wire, the time constant in the cooling
phase will likely make this infeasible.
That sounds like a good excuse to build a bigger and more impressive
pendulum. You need a longer wire so it has a longer period and enough time
to cool off.



Does anybody know how much piezo positioners cost, or where to get them
cheap? I'm not looking for a fancy gizmo that takes many tiny steps, just a
something simple that will vary the height slightly.

Maybe build one from several piezo noisemakers.

Here is the fun part. You can also use it as a sensor to measure the
position.
--
These are my opinions, not necessarily my employer's. I hate spam.
Demian Martin
2010-07-23 02:20:31 UTC
Permalink
Another perspective on time: http://www.longnow.org/clock/

And some fascinating mechanical stuff.

-Demian





Message: 4

Date: Fri, 23 Jul 2010 02:11:04 +0200

From: Magnus Danielson <magnus-0aYeopylZ8Qi5CQI31g/s0B+***@public.gmane.org>

Subject: Re: [time-nuts] A different timenuts interest

To: Discussion of precise time and frequency measurement

<time-nuts-***@public.gmane.org>

Message-ID: <4C48DE18.7040806-0aYeopylZ8Qi5CQI31g/s0B+***@public.gmane.org>

Content-Type: text/plain; charset=ISO-8859-1; format=flowed
Post by Oz-in-DFW
Hmmm. I thought time-nuts were nuts about time, with branch interests
in accuracy, resolution, history...
History is nanoseconds ago.

Recent history is picoseconds ago.

Just now is femtoseconds ago.

Fraction of mind ago is attoseconds ago.

Acient history is microseconds ago.

Ages is microseconds ago

Major epochs in time i seconds ago.

Geological short period is minutes ago.

Geological epoch period is hours ago.



No?



Cheers,

Magnus
Morris Odell
2010-07-23 03:20:37 UTC
Permalink
Hi all,

I would like to thank everyone who responded to my post. This is a wonderful
group of talented and erudite people and it was a pleasure to read the posts
(and private emails) on the subject of the Foucault pendulum. Where else
could the discussion range over timekeeping, mechanical suspension
arrangements, Tesla coils, Napoleon, sustaining systems, blades on the
pendulum bob, a host of references and all the other great stuff that turned
up.

This project is for a FP that will be part of an art installation. It's
unlikely to be permanent though unless a major gallery or collector likes
the work enough to buy it. Unfortunately this rules out commercial systems
costing tens of thousands of dollars.
From my readings and suggestions from members of this group I have come to
understand the following:

The main issues in designing a FP are the sustaining system, avoidance or
damping of elliptical motion and safety considerations in case the wire
breaks. Of course keeping fingers and draughts away is also a consideration.


Sustaining systems are mostly electromagnetic, either with a ring shaped
electromagnet at the top near the suspension point controlled by optical
sensors, or one or more coils below the centre point with a magnet on the
bob. This acts as both a sensor and "motor". There is also a reluctance type
driver described using mains frequency solenoids. The most elegant system is
the parametric one where the suspension point is oscillated up and down
sinusoidally at twice the pendulum frequency and there are no horizontal
forces acting on the bob at all. I found a very complex mathematical
analysis if that. It would be an interesting challenge using optical sensors
and a stepper perhaps to move a cam or crank to realise that.

Avoidance of elliptical motion and increasing the Q of the oscillator is one
of the reasons why most FPs are so long with heavy bobs. Despite this I
found some articles on short FPs, including one hanging from the wall and
used as a clock with a pendulum less than a metre long. Elliptical movement
is often controlled by a "Charron ring" which interacts with the wire to
limit ellipsoidal movement. There are also magnetic eddy current damping
systems described and one elegant method which uses a precisely timed pulsed
sustaining system to cancel elliptical motion.

As was pointed out, FPs are not primarily time keeping devices but there is
a relationship between the period of their precession and the rotation of
the planet, which is also dependent on Latitude. Perhaps unsurprisingly,
someone has described a FP clock which required an electronic system to stop
it for a few hours in the middle of the night to sync its movement to the 24
hour cycle. One can easily see GPS control creeping in there :-)

I hope the discussion continues, It's been great so far. I'll keep the group
posted on progress.

Cheers,

Morris
Bob Camp
2010-07-23 16:57:52 UTC
Permalink
Hi

How much room do you have for the pendulum? Size is going to impact the
choice of designs quite a bit.

Bob

-----Original Message-----
From: time-nuts-bounces-***@public.gmane.org [mailto:time-nuts-bounces-***@public.gmane.org] On
Behalf Of Morris Odell
Sent: Thursday, July 22, 2010 11:21 PM
To: time-nuts-***@public.gmane.org
Subject: Re: [time-nuts] A different timenuts interest

Hi all,

I would like to thank everyone who responded to my post. This is a wonderful
group of talented and erudite people and it was a pleasure to read the posts
(and private emails) on the subject of the Foucault pendulum. Where else
could the discussion range over timekeeping, mechanical suspension
arrangements, Tesla coils, Napoleon, sustaining systems, blades on the
pendulum bob, a host of references and all the other great stuff that turned
up.

This project is for a FP that will be part of an art installation. It's
unlikely to be permanent though unless a major gallery or collector likes
the work enough to buy it. Unfortunately this rules out commercial systems
costing tens of thousands of dollars.
From my readings and suggestions from members of this group I have come to
understand the following:

The main issues in designing a FP are the sustaining system, avoidance or
damping of elliptical motion and safety considerations in case the wire
breaks. Of course keeping fingers and draughts away is also a consideration.


Sustaining systems are mostly electromagnetic, either with a ring shaped
electromagnet at the top near the suspension point controlled by optical
sensors, or one or more coils below the centre point with a magnet on the
bob. This acts as both a sensor and "motor". There is also a reluctance type
driver described using mains frequency solenoids. The most elegant system is
the parametric one where the suspension point is oscillated up and down
sinusoidally at twice the pendulum frequency and there are no horizontal
forces acting on the bob at all. I found a very complex mathematical
analysis if that. It would be an interesting challenge using optical sensors
and a stepper perhaps to move a cam or crank to realise that.

Avoidance of elliptical motion and increasing the Q of the oscillator is one
of the reasons why most FPs are so long with heavy bobs. Despite this I
found some articles on short FPs, including one hanging from the wall and
used as a clock with a pendulum less than a metre long. Elliptical movement
is often controlled by a "Charron ring" which interacts with the wire to
limit ellipsoidal movement. There are also magnetic eddy current damping
systems described and one elegant method which uses a precisely timed pulsed
sustaining system to cancel elliptical motion.

As was pointed out, FPs are not primarily time keeping devices but there is
a relationship between the period of their precession and the rotation of
the planet, which is also dependent on Latitude. Perhaps unsurprisingly,
someone has described a FP clock which required an electronic system to stop
it for a few hours in the middle of the night to sync its movement to the 24
hour cycle. One can easily see GPS control creeping in there :-)

I hope the discussion continues, It's been great so far. I'll keep the group
posted on progress.

Cheers,

Morris




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Hal Murray
2010-07-23 06:20:53 UTC
Permalink
Post by Demian Martin
Another perspective on time: http://www.longnow.org/clock/
And some fascinating mechanical stuff.
The mechanical branch of time-nuts.

They have an office, show-room, museum, store, whatever in Fort Mason in San
Francisco. If you like neat mechanical stuff, it's well worth a trip. It's
art as well as a clock.

http://www.longnow.org/contact/
(The map/picture is looking southeast from over the Golden Gate Bridge.)
--
These are my opinions, not necessarily my employer's. I hate spam.
Bob Bownes
2012-10-04 17:56:44 UTC
Permalink
On Thu, 4 Oct 2012 13:04:27 -0400
The problem stems from one of the two (identical) machines drifting off
by
60-70 seconds per day. So a few ms here and there are ok.
Is it drifting without ntp or with ntp?
1minute drift per day is not unheard of for standard PC RTCs.. i've seen
even worse..
With. Hence the issue.

<redacted>
So, if you have any significant time difference (>1ms) between two systems
that synchronize to the same NTP server in the same LAN, then the
problem lies somewhere else than the network.
Exactly where I am at this point. Dozen of other systems in the same
facility don't seem to have this issue.
Bob Bownes
2012-10-04 17:04:27 UTC
Permalink
Post by Bob Bownes
Due to reasons I really can't go into, a systems user is concerned with
the
displacement of two servers from the same pair of stratum 2 NTP servers.
<redacted>
Assuming you are running the standard ntpd... It includes all sorts of
logging.
Set up the two systems so they use each other as servers. Turn on
rawstats.
ntpd will add a line each time it exchanges a pair of packets with a
server.
That line will have the IP Address and 4 time stamps. See the
time the request left the local system
time the request arrived at the remote system
time the response left the remote system
time the response arrived at the local system
That looks like a bit of overkill. :)
If you subtract the first two, you get the network transit time for the
request packet as skewed by the clock offset. Subtracting the last two
gives
you the transit time for the response packet.
If you assume the network transit times are equal, you can compute the
clock
offset. If you are on a LAN, the transit times will probably be tiny on
the
scale of 10s of ms.
In this case, the transit times should average out be very very close. The
two machines in question are plugged into adjacent network ports with the
same length of cable and the NTP server is on the same (lightly loaded) sub
net.

The problem stems from one of the two (identical) machines drifting off by
60-70 seconds per day. So a few ms here and there are ok.


How good is your connection to the big bad internet? If you run a big
Post by Bob Bownes
download over a slow link, the queuing delays can confuse ntp. You might
want to look at the timings from your systems to the stratum-2 servers
and/or
from the stratum-2 servers to the outside world.
This is all relative to two internal stratum 2 servers on the same command
and control network. No large xfers allowed over it. There are physically
separate data, backup, and application networks for that.

Thanks for the suggestions folks. I'm going to look into some of the
standard ntp logging stuff as well as the scripts that John offered up. And
now, I'm probably going to have set something up to start comparing my 3
GPSDO's and their associated machines! :)

As an aside, I have seen that someone on the Raspberry Pi list has NTP
running with 1pps into the GPIO ports. I've got a stack of GPS modules in
stock with 1pps that are just itching to be tied to one of those, also in
stock. Maybe this weekend.

Bob
Attila Kinali
2012-10-04 17:31:39 UTC
Permalink
On Thu, 4 Oct 2012 13:04:27 -0400
Post by Bob Bownes
The problem stems from one of the two (identical) machines drifting off by
60-70 seconds per day. So a few ms here and there are ok.
Is it drifting without ntp or with ntp?
1minute drift per day is not unheard of for standard PC RTCs.. i've seen
even worse..
Post by Bob Bownes
This is all relative to two internal stratum 2 servers on the same command
and control network. No large xfers allowed over it. There are physically
separate data, backup, and application networks for that.
On the average LAN (ie one that is connected by a couple of switches.
No routers inbetween), the RTT will be dominated by the minimum packet
times of ethernet. That's where the 200us delay comes from (actually
it's below 1us for Gbit, but for some reason i've never seen it go under
100us). With modern switches that do worm-hole routing (ie just use the
destination address in the first few bytes and then pass the packet on
without further delay, while the "end" of the packet is still on the wire
and not yet received by the switch) you dont even get much added delay
from using multiple switches in line. With such large delays you can ignore
any wire delay completely (which is in the range of 1us for maximum length
cable).

With routers it looks a bit different, there the whole packet is first
stored in memory before being processed (due to more complicated routing
decision). Due to this, RTT is still dominated by delay of the network
hardware and not speed of light. Actually speed of light related delays
will be buried deep in the noise unless you go trans-continental.
And even then, router delay will still dominate. (eg RTT Europe-Japan
is around 500ms, by which time a packet would be half way to the moon)

So, if you have any significant time difference (>1ms) between two systems
that synchronize to the same NTP server in the same LAN, then the
problem lies somewhere else than the network.


Attila Kinali
--
There is no secret ingredient
-- Po, Kung Fu Panda
David J Taylor
2012-10-05 04:30:54 UTC
Permalink
The problem stems from one of the two (identical) machines drifting off by
60-70 seconds per day. So a few ms here and there are ok.
[]
Bob
==================================

Bob,

NTP is normally limited to a +/- 500 parts per million correction - 43
seconds per day. You may be operating outside the range NTP is expecting to
handle. If the clock offset is a stable value of 60-70 seconds per day you
can bias NTP to correct within +/- 500 ppm of that drift.

Cheers,
David
--
SatSignal Software - Quality software written to your requirements
Web: http://www.satsignal.eu
Email: david-taylor-***@public.gmane.org
Bob Bownes
2012-10-05 04:42:42 UTC
Permalink
David,

The problem is that they start in sync and over the course of a day drift that far apart despite having NTP running. We're not sure why NTP isn't correcting it along the way. Though at this point, we are looking at a firmware bug.

Thanks!
Bob
Post by Bob Bownes
The problem stems from one of the two (identical) machines drifting off by
60-70 seconds per day. So a few ms here and there are ok.
[]
Bob
==================================
Bob,
NTP is normally limited to a +/- 500 parts per million correction - 43 seconds per day. You may be operating outside the range NTP is expecting to handle. If the clock offset is a stable value of 60-70 seconds per day you can bias NTP to correct within +/- 500 ppm of that drift.
Cheers,
David
--
SatSignal Software - Quality software written to your requirements
Web: http://www.satsignal.eu
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and follow the instructions there.
David
2012-10-05 05:34:20 UTC
Permalink
I had an early Phenom II that lost time while turned on but the
internal CMOS clock did not so rebooting or reading the CMOS clock
restored the correct time. There was a problem with the System
Management Mode code and The C1E CPU state which was new at that time
where an interrupt was being lost. Disabling the low power CPU state
fixed it until a BIOS update was released.

It has been a while but as I recall, the NTP client kept the OS from
drifting further behind but the time was still noticeably off.
Post by Bob Bownes
David,
The problem is that they start in sync and over the course of a day drift that far apart despite having NTP running. We're not sure why NTP isn't correcting it along the way. Though at this point, we are looking at a firmware bug.
Thanks!
Bob
Post by Bob Bownes
The problem stems from one of the two (identical) machines drifting off by
60-70 seconds per day. So a few ms here and there are ok.
[]
Bob
==================================
Bob,
NTP is normally limited to a +/- 500 parts per million correction - 43 seconds per day. You may be operating outside the range NTP is expecting to handle. If the clock offset is a stable value of 60-70 seconds per day you can bias NTP to correct within +/- 500 ppm of that drift.
Cheers,
David
--
SatSignal Software - Quality software written to your requirements
Web: http://www.satsignal.eu
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David J Taylor
2012-10-05 08:46:37 UTC
Permalink
David,

The problem is that they start in sync and over the course of a day drift
that far apart despite having NTP running. We're not sure why NTP isn't
correcting it along the way. Though at this point, we are looking at a
firmware bug.

Thanks!
Bob
===================================

Bob,

I take it that you are booting the PC at the start of the day, and it syncs
to NTP servers at that time? If the internal clock is off (when
undisciplined) by more than 500 ppm (43 seconds/day) NTP will not control
it. I suggest measuring the clock error when it is not being controlled by
NTP, and then we can progress. (Or you find the firmware problem).

Cheers,
David
--
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Christopher Brown
2012-10-05 18:23:56 UTC
Permalink
That is his point.

Initial time comes from MB clock.

System (OS) time is set from that at boot.

During NTP startup for a client it is normal to do a "ntpdate" to hard
set the OS clock (direct one time set).
From there ntpd would track and adjust.
HOWEVER, there are limits to how much ntpd will skew the clock to keep
it in sync. If the OS clock is drifting faster than this amount ntpd
will not be able to adjust it fast enough.


Think bad hardware or buggy BIOS, OS clock ends up running too fast or
too slow for ntpd to compensate for.
David,
The problem is that they start in sync and over the course of a day drift
that far apart despite having NTP running. We're not sure why NTP isn't
correcting it along the way. Though at this point, we are looking at a
firmware bug.
Thanks!
Bob
===================================
Bob,
I take it that you are booting the PC at the start of the day, and it syncs
to NTP servers at that time? If the internal clock is off (when
undisciplined) by more than 500 ppm (43 seconds/day) NTP will not control
it. I suggest measuring the clock error when it is not being controlled by
NTP, and then we can progress. (Or you find the firmware problem).
Cheers,
David
Magnus Danielson
2012-10-05 22:38:48 UTC
Permalink
Post by Christopher Brown
That is his point.
Initial time comes from MB clock.
System (OS) time is set from that at boot.
During NTP startup for a client it is normal to do a "ntpdate" to hard
set the OS clock (direct one time set).
From there ntpd would track and adjust.
HOWEVER, there are limits to how much ntpd will skew the clock to keep
it in sync. If the OS clock is drifting faster than this amount ntpd
will not be able to adjust it fast enough.
Think bad hardware or buggy BIOS, OS clock ends up running too fast or
too slow for ntpd to compensate for.
Buggy OS has been known to do this before. Lack of kernel support is a
real killer. What are you running?

There is another point to make for servers. Since NTP will not trust
clocks being more than +/- 15 min away from the system time, if the HW
clock drifted to far away over the months and maybe years since boot,
then when it initiate the system time on next boot it may lock the NTP
training out. A good way to mitigate this is to have a cron job to
transfer system time over to HW clock time regularly, maybe once a week
or once a month. That way, if the server goes down uncontrolled (at
which time it is expected to do this, if you are lucky) the HW clock
won't be too far off anyway for things to resolve itself by automagic.

Oh, I learned this the hard way when we had a power failure in the
computer hall.

Cheers,
Magnus
Hal Murray
2012-10-04 16:46:38 UTC
Permalink
Due to reasons I really can't go into, a systems user is concerned with the
displacement of two servers from the same pair of stratum 2 NTP servers.
I'm convinced that it really isn an issue as long as the two systems in
question remain within a few 10's of ms. However, I have no off the shelf
method of collecting and correlating the data. Before I go out and invent
the wheel, I thought I would check and see if anyone has done such a thing
and saved the scripts and whatnot.
Assuming you are running the standard ntpd... It includes all sorts of
logging.

Set up the two systems so they use each other as servers. Turn on rawstats.
ntpd will add a line each time it exchanges a pair of packets with a server.
That line will have the IP Address and 4 time stamps. See the
documentation. Details are in monopt.html The 4 time stamps are:
time the request left the local system
time the request arrived at the remote system
time the response left the remote system
time the response arrived at the local system

If you subtract the first two, you get the network transit time for the
request packet as skewed by the clock offset. Subtracting the last two gives
you the transit time for the response packet.

If you assume the network transit times are equal, you can compute the clock
offset. If you are on a LAN, the transit times will probably be tiny on the
scale of 10s of ms.

(If you assume the clocks are both accurate, you can compute the network
transit time in each direction.)

If you want to graph the results, you have to split out the lines for the
server you are interested in. Then you can feed it to gnuplot/whatever.


You can also do the monitoring from another system, but then you have to sort
out what happens when the clock on that system is off.


How good is your connection to the big bad internet? If you run a big
download over a slow link, the queuing delays can confuse ntp. You might
want to look at the timings from your systems to the stratum-2 servers and/or
from the stratum-2 servers to the outside world.
--
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Hal Murray
2012-10-05 22:26:14 UTC
Permalink
Post by Bob Bownes
The problem is that they start in sync and over the course of a day drift
that far apart despite having NTP running. We're not sure why NTP isn't
correcting it along the way. Though at this point, we are looking at a
firmware bug.
I wouldn't think of it as two systems drifting apart, but rather at least one
system with a broken clock.

Is it only one system that is broken?

How many systems do you have running the same firmware? OS? Hardware?
Are the two systems that drift apart running on the same hardware and OS?
Do any other similar systems have troubles?

I wouldn't rule out an OS or ntpd bug.

It's fairly easy to set up a system to monitor the time on several/many other
systems. For each system you want to monitor, add a line like this to your
ntp.conf:
server xxxx noselect minpoll x maxpoll y
ntpq -p will quickly show you any boxes that are way out of tune. Anything
off by a second will stand out. Or scan rawstats or peerstats.

noselect goes through all the work of polling the target site, including
logging, but then discards the data rather than using it to control the local
clock. It's great for monitoring other systems.


Normally, if ntpd is off by more than 128 ms, it will step the clock. That
puts a line in the log file. So it's more than a bit strange that the clocks
get off by many seconds.

I'd double check that ntpd really is still running.

Are your drift-apart systems using only your 2 local stratum-2 servers? If
so, that may be the problem. If those servers don't agree, which one do you
believe? (There is endless discussion in the NTP community about how many
servers you need. 3 lets you out-vote 1 bad guy. 4 lets you out-vote a bad
guy if one of them is down. ...)
--
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bownes
2012-10-05 22:57:03 UTC
Permalink
Comments inline.
Post by Hal Murray
Post by Bob Bownes
The problem is that they start in sync and over the course of a day drift
that far apart despite having NTP running. We're not sure why NTP isn't
correcting it along the way. Though at this point, we are looking at a
firmware bug.
I wouldn't think of it as two systems drifting apart, but rather at least one
system with a broken clock.
Correct.
Post by Hal Murray
Is it only one system that is broken?
Sort of. There are several systems consisting of a matched pair of nodes. In each case, one of the two wanders out into the weeds. But not every pair has one that goes south.

In this case, four systems, 8 nodes, all identical hw (sequential sn's even), identical iLOM/DRAC, same software the entire length of the stack.

Installing the latest firmware patch appears to have solved the problem. I'll know next week.
Post by Hal Murray
How many systems do you have running the same firmware?
<redacted>
Post by Hal Murray
Normally, if ntpd is off by more than 128 ms, it will step the clock. That
puts a line in the log file. So it's more than a bit strange that the clocks
get off by many seconds.
My thinking exactly. But it wasn't. I was hoping to use some tools to watch it drift off.
Post by Hal Murray
I'd double check that ntpd really is still running.
It is.
Post by Hal Murray
Are your drift-apart systems using only your 2 local stratum-2 servers? If
so, that may be the problem. If those servers don't agree, which one do you
believe? (There is endless discussion in the NTP community about how many
servers you need. 3 lets you out-vote 1 bad guy. 4 lets you out-vote a bad
guy if one of them is down. ...)
Two NTP servers agree. They even agree with my S1 at home. :)

Thanks for all the help folks. It looks like it was a firmware bug, even if I can't explain how the firmware was causing the NTP clock to be off.
Hal Murray
2013-05-27 00:17:46 UTC
Permalink
For making a blinking LEDs, it is hard to beat a 74LS74. However, a PIC, is
probably less expensive! :)
Thanks. :)

I was going to send a wise-ass comment, but then I checked some numbers.

Digikey, one-off DIP pricing:
$0.62 SN74LS74
$0.55 PIC10F200
$0.33 SN74HC74

So technically you are correct, but only because you are picked an ancient
technology.

Besides, the '74 needs a clock while the PIC has an internal clock calibrated
to 1%.

I suspect what's going on is that the '74 is pad limited(*) so you are paying
per-pad rather than per gate. The PIC only has 8 pins, so if it's close to
pad limited it will be cheaper.

The PIC10F200 has 3 output pins so it can blink 3 LEDs independently while
the '74 only has 2 FFs.

High volume (whole tape, 2-3K) prices are $0.34, 0.22, and 0.10

------

*) If you aren't familiar with pad-limited, it's a cool idea. Consider a
chip that has N pins. Each pin needs a pad for the bond wire. Arrange those
in a rectangle around the perimeter of your chip. That leaves a hole in the
middle. Put your logic in there. If it doesn't fit, push the pads out until
there is room. That makes your chip bigger and more expensive. If it fits
with room leftover, you can add more logic for free. That's why low cost
watches have so many features.
--
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Bob Camp
2013-05-27 01:07:27 UTC
Permalink
Hi

Ok, *but*

Power?
Mounting / circuit board?
LED's?
Resistors?
Bypass caps?
Control inputs?

I believe I first learned how fast wire turns into "something else" when there's a short while JFK was president. That lesson in doing things quick and dirty has stuck with me. If a gizmo is going to keep running for quite a while you need to make it right. The original start to this thread was something that should work for years. The cost of wiring it up (PCB etc) will dwarf the cost of the CPU.

Even with something simple (actually especially with something simple) all that stuff is going to add up. Even more so if you want the result to be reasonably rugged. Can you scramble wire it to a set of D cells and steal the LED's from a kid's toy? - sure. Does that make the rest of it free? - not so much. Doubly so when the kid comes looking for the toy :).

Free parts can be a slippery thing. First simple test - can a total stranger (who keeps a neat house) get one for free as well? I can probably get all sorts of things "for free" if I use the work phone to make the call. That does not pass the test….. Second simple test - can I make 100 of them for a lower cost? Cost should go down as volume goes up….

If the objective is a time related gizmo (this being TimeNuts) simply making the LED blink can't be the the end of it. It's *got* to display the ADEV of the lunar orbit in morse code or some other highly useful thing. If it doesn't do something like that it's (possibly) off topic for the list. Turning this from a simple $ XX LED blinker to something much more complex probably adds less than 10% to the total cost.

Optimizing one aspect of a design without considering the rest of it is rarely a good idea. Assuming your time is worthless generally leads to projects that don't complete. For that matter McDonalds will happily pay you minimum wage for your time. My apologies to those who enjoy hours of soldering mag wire in 3D constructs, most of us don't look at that as a learning experience the 100th time around. Most of the really fun stuff is done quickly, the rest of it - McDonalds is "fun" as well….Your time *always* has a cash value.

That said - the 74LS74 isn't all that good at driving LED's - not a lot of current drive on those outputs. Same is true of the 74HC74. The 74AC74 is the one you want, 52 cents one up DIP at Digikey.

Bob
Post by Hal Murray
For making a blinking LEDs, it is hard to beat a 74LS74. However, a PIC, is
probably less expensive! :)
Thanks. :)
I was going to send a wise-ass comment, but then I checked some numbers.
$0.62 SN74LS74
$0.55 PIC10F200
$0.33 SN74HC74
So technically you are correct, but only because you are picked an ancient
technology.
Besides, the '74 needs a clock while the PIC has an internal clock calibrated
to 1%.
I suspect what's going on is that the '74 is pad limited(*) so you are paying
per-pad rather than per gate. The PIC only has 8 pins, so if it's close to
pad limited it will be cheaper.
The PIC10F200 has 3 output pins so it can blink 3 LEDs independently while
the '74 only has 2 FFs.
High volume (whole tape, 2-3K) prices are $0.34, 0.22, and 0.10
------
*) If you aren't familiar with pad-limited, it's a cool idea. Consider a
chip that has N pins. Each pin needs a pad for the bond wire. Arrange those
in a rectangle around the perimeter of your chip. That leaves a hole in the
middle. Put your logic in there. If it doesn't fit, push the pads out until
there is room. That makes your chip bigger and more expensive. If it fits
with room leftover, you can add more logic for free. That's why low cost
watches have so many features.
--
These are my opinions. I hate spam.
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Charles P. Steinmetz
2013-05-28 19:25:13 UTC
Permalink
I wanted to take this opportunity to thank everyone who has
contributed so much wisdom on this and the other two microcontroller
threads. The last time I personally designed with uCs was 25+ years
ago. Much has changed, and you have given me lots to think about!

Of course, there was no unanimity in the suggestions, but everyone
did a very nice job of telling it as they see it, without any
religious fervor. I also appreciate the in-depth discussion of
development environments and operating systems, as well as hardware
capabilities.

Ultimately, it seems likely that I will end up choosing two or three
uCs to learn, maybe from the same family, maybe not. It probably
makes the most sense to start at the bottom, with an anticipatory eye
toward which midrange uC I will take up next. I expect it will be
quite some time before I need a third part ("very fancy" uC). At
this point, I seem to be favoring parts with flash that support an
RTOS, can be removed from the development board and installed into
the system board, and have a good, low-cost development platform (so,
I appear to have narrowed it down to only several thousand different parts...).

Again, thank you all for your comments. I am still at the foothills
of the learning curve, but I know much, much more than I did a week ago.

Finally, please do not take this message as a sign to abandon these
threads, if there is more worthwhile to say.

Thanks again to all,

Charles
Hal Murray
2015-10-14 22:23:35 UTC
Permalink
I never figured out if it was using line frequency zero crossings for
seconds or if it was leaking as DEC fixed it not long after it was
installed. (And it was moved to a different phase of the power system than
the clocks...)
I remember a story from ages ago... A machine was keeping crappy time. It
was a 60 Hz box running in a 50 Hz country. Things got a lot better after
the frequency converter box was adjusted.
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Hal Murray
2018-06-15 04:20:01 UTC
Permalink
I’m still hunting for something that will take NTP in and put IRIG out. There
is probably someone doing it with a Pi or an Arduino.
There is a module in the ntp package/collection that puts out IRIG from the
system clock. You can use NTP if you want to keep your clock sane. I forget
the name. I'll fish it out if you can't find it.
--
These are my opinions. I hate spam.
Bob Bownes
2018-06-15 15:04:05 UTC
Permalink
Hal,

I remember there being such a thing, but a search of the ntp site turns up
nothing. Anything you can provide would be most welcome.

Thanks!
Bob
Post by Hal Murray
I’m still hunting for something that will take NTP in and put IRIG out.
There
is probably someone doing it with a Pi or an Arduino.
There is a module in the ntp package/collection that puts out IRIG from the
system clock. You can use NTP if you want to keep your clock sane. I forget
the name. I'll fish it out if you can't find it.
--
These are my opinions. I hate spam.
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Jerry Hancock
2018-06-15 15:19:33 UTC
Permalink
One of the cheapest NTP servers that can be built would be an arduino Uno, CE version for around $10, an LCD display shield with buttons for $15 and an Ethernet shield for $8.95. But getting all that to stack didn’t work, so I had to use jumpers to the LCD part shield.

Then add one of the 6 or more 1PPS signals you have strung all over and off you go.

I only played around with the ethernet shield, did some TCP pipes, never finished the server but it wouldn’t be hard.

Regards,

Jerry
Post by Bob Bownes
Hal,
I remember there being such a thing, but a search of the ntp site turns up
nothing. Anything you can provide would be most welcome.
Thanks!
Bob
Post by Hal Murray
I’m still hunting for something that will take NTP in and put IRIG out.
There
is probably someone doing it with a Pi or an Arduino.
There is a module in the ntp package/collection that puts out IRIG from the
system clock. You can use NTP if you want to keep your clock sane. I forget
the name. I'll fish it out if you can't find it.
--
These are my opinions. I hate spam.
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paul swed
2018-06-15 15:31:05 UTC
Permalink
By the way I have hacked IRIG B using a proc called SXB and basic language.
The specs are out there and its not all that hard.
Two tricks that really simplify it. (Everything could be done in software)
Use a stable external sine wave 1 KHz oscillator. I used a epson dip
oscillator pretty stable. (Not in a time-nuts sense)
Use an external amplitude modulator (Big words a switch) CD 4066 as an
example.
Thats what I did. By doing that the software is just changing the GPS code
to the serial irig code.
Regards
Paul
Post by Jerry Hancock
One of the cheapest NTP servers that can be built would be an arduino Uno,
CE version for around $10, an LCD display shield with buttons for $15 and
an Ethernet shield for $8.95. But getting all that to stack didn’t work,
so I had to use jumpers to the LCD part shield.
Then add one of the 6 or more 1PPS signals you have strung all over and off you go.
I only played around with the ethernet shield, did some TCP pipes, never
finished the server but it wouldn’t be hard.
Regards,
Jerry
Post by Bob Bownes
Hal,
I remember there being such a thing, but a search of the ntp site turns
up
Post by Bob Bownes
nothing. Anything you can provide would be most welcome.
Thanks!
Bob
Post by Hal Murray
I’m still hunting for something that will take NTP in and put IRIG out.
There
is probably someone doing it with a Pi or an Arduino.
There is a module in the ntp package/collection that puts out IRIG from the
system clock. You can use NTP if you want to keep your clock sane. I forget
the name. I'll fish it out if you can't find it.
--
These are my opinions. I hate spam.
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Post by Bob Bownes
and follow the instructions there.
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Martin VE3OAT
2018-06-15 16:10:13 UTC
Permalink
What about the clock part of the old AN/GSQ-53A frequency/time rack?

It wasn't NTP of course, but ran off of 1 MHz (as I recall) and
generated IRIG-B for remote displays. The rack included a nice Sulzer
crystal oscillator (plus a spare), later upgraded to HP rubidium RVFS
(5061A?).

There must have been thousands of them made for US DoD and NASA. We
had at least a dozen in Canada that I know of (5 field sites, plus
spares).

Where did they all go?

... Martin VE3OAT


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Bob kb8tq
2018-06-15 16:52:11 UTC
Permalink
Hi

I suspect part of the answer is “they are cool looking stuff, grab it when it’s swapped out” ….
They are out there, but not on the surplus market.

Bob
Post by Martin VE3OAT
What about the clock part of the old AN/GSQ-53A frequency/time rack?
It wasn't NTP of course, but ran off of 1 MHz (as I recall) and generated IRIG-B for remote displays. The rack included a nice Sulzer crystal oscillator (plus a spare), later upgraded to HP rubidium RVFS (5061A?).
There must have been thousands of them made for US DoD and NASA. We had at least a dozen in Canada that I know of (5 field sites, plus spares).
Where did they all go?
... Martin VE3OAT
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David Andersen
2018-06-15 17:17:10 UTC
Permalink
Thanks, all - sounds like either finding a cheap IRIG display or hacking up
a pi/arduino/etc. version will be the path forward. The IRIG displays I
can find quickly on ebay are still priced for people building music
studios, so...

RPi 3 B+ supports PoE with an extra hat, and you can get pi-powered 3.5"
TFTs cheaply. This may work best.

A friend also pointed me to some networked dot-matrix displays that will do
NTP from timemachinescorp, which might be a fun diversion. :); -Dave


-Dave
Post by Bob kb8tq
Hi
I suspect part of the answer is “they are cool looking stuff, grab it when
it’s swapped out” ….
They are out there, but not on the surplus market.
Bob
Post by Martin VE3OAT
What about the clock part of the old AN/GSQ-53A frequency/time rack?
It wasn't NTP of course, but ran off of 1 MHz (as I recall) and
generated IRIG-B for remote displays. The rack included a nice Sulzer
crystal oscillator (plus a spare), later upgraded to HP rubidium RVFS
(5061A?).
Post by Martin VE3OAT
There must have been thousands of them made for US DoD and NASA. We had
at least a dozen in Canada that I know of (5 field sites, plus spares).
Post by Martin VE3OAT
Where did they all go?
... Martin VE3OAT
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paul swed
2018-06-15 18:21:49 UTC
Permalink
My reason to hack up a nice clock display is because no matter what I can't
make my home brew stuff look as nice.
So to me its a pile of displays in a nice rack box that I hook a processor
to and do what ever I like.
Reversing out the display methods pretty easy as they are typically
multiplexed.
I use Truetime DC 468 7 segment panelplex displays this way. Just like the
looks.
Regards
Post by David Andersen
Thanks, all - sounds like either finding a cheap IRIG display or hacking up
a pi/arduino/etc. version will be the path forward. The IRIG displays I
can find quickly on ebay are still priced for people building music
studios, so...
RPi 3 B+ supports PoE with an extra hat, and you can get pi-powered 3.5"
TFTs cheaply. This may work best.
A friend also pointed me to some networked dot-matrix displays that will do
NTP from timemachinescorp, which might be a fun diversion. :); -Dave
-Dave
Post by Bob kb8tq
Hi
I suspect part of the answer is “they are cool looking stuff, grab it
when
Post by Bob kb8tq
it’s swapped out” ….
They are out there, but not on the surplus market.
Bob
Post by Martin VE3OAT
What about the clock part of the old AN/GSQ-53A frequency/time rack?
It wasn't NTP of course, but ran off of 1 MHz (as I recall) and
generated IRIG-B for remote displays. The rack included a nice Sulzer
crystal oscillator (plus a spare), later upgraded to HP rubidium RVFS
(5061A?).
Post by Martin VE3OAT
There must have been thousands of them made for US DoD and NASA. We
had
Post by Bob kb8tq
at least a dozen in Canada that I know of (5 field sites, plus spares).
Post by Martin VE3OAT
Where did they all go?
... Martin VE3OAT
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Bob kb8tq
2018-06-15 18:29:37 UTC
Permalink
Hi

There are an enormous number of displays out there that will interface with the little boards. You can spend a little or you
can spend a *lot*. At least in terms of size, it is a bit of a “you get what you pay for” sort of thing. Some of the larger LED
arrays look pretty impressive. Cost wise … yikes …..

You also get off into a whole variety of rabbit holes to wander down. Do you want to be able to use voice commands to change
what the clock shows? ….. lots of ways to soak up a lot of time ….

Bob
Thanks, all - sounds like either finding a cheap IRIG display or hacking up a pi/arduino/etc. version will be the path forward. The IRIG displays I can find quickly on ebay are still priced for people building music studios, so...
RPi 3 B+ supports PoE with an extra hat, and you can get pi-powered 3.5" TFTs cheaply. This may work best.
A friend also pointed me to some networked dot-matrix displays that will do NTP from timemachinescorp, which might be a fun diversion. :); -Dave
-Dave
Hi
I suspect part of the answer is “they are cool looking stuff, grab it when it’s swapped out” ….
They are out there, but not on the surplus market.
Bob
Post by Martin VE3OAT
What about the clock part of the old AN/GSQ-53A frequency/time rack?
It wasn't NTP of course, but ran off of 1 MHz (as I recall) and generated IRIG-B for remote displays. The rack included a nice Sulzer crystal oscillator (plus a spare), later upgraded to HP rubidium RVFS (5061A?).
There must have been thousands of them made for US DoD and NASA. We had at least a dozen in Canada that I know of (5 field sites, plus spares).
Where did they all go?
... Martin VE3OAT
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Hal Murray
2018-06-15 20:52:14 UTC
Permalink
I’m still hunting for something that will take NTP in and put IRIG out.
There is probably someone doing it with a Pi or an Arduino.
I remember there being such a thing, but a search of the ntp site turns up
nothing. Anything you can provide would be most welcome.
Try util/tg2.c

It hasn't changed since 2011, so any ntp source tar file since then should
have it.
--
These are my opinions. I hate spam.
Dave B via time-nuts
2018-06-16 12:47:15 UTC
Permalink
Hi.

Others have done similar with a Raspberry Pi and display for very much
less cost.  There are several examples described on personal pages if
you search.  Re-purposed Android tablet's could also be used too, as I
have used in the past.

There are PoE conversions for the Pi's as well, if needed.

Regards.

Dave B.

------------------------------------------------------------------------
Subject: [time-nuts] Affordable PoE 6-digit time displays?
Content-Type: text/plain; charset="UTF-8"
I'd hoped that ebay or aliexpress would yield a bounty given how seemingly
simple these are, but I'm drawing a blank (and finding a lot of $300+ new
options). Anyone have a favorite source for either flat wall-mount or
rackmount displays that will pull from an NTP/SNTP/whatever server?
(if wall-mount, PoE is optimal). Used good. Cheap good. Looks good next
to my random collection of antiquated time measurement gear provides
amusement value but isn't really critical. :-)
Thanks!
-Dave
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Jeff Woolsey
2018-06-19 03:57:48 UTC
Permalink
Post by Dave B via time-nuts
Others have done similar with a Raspberry Pi and display for very much
less cost.  There are several examples described on personal pages if
you search. 
Indeed.  I did that with a 240-volt German-labelled ELV DCF7000 I found
at weirdstuff.  The Pi generates baseband DCF77 timecode for it.  It's
also an NTP server, so the display is acccurate.
--
Jeff Woolsey {{woolsey,jlw}@jlw,first.last@{gmail,jlw}}.com
Nature abhors straight antennas, clean lenses, and empty storage.
"Delete! Delete! OK!" -Dr. Bronner on disk space management
Card-sorting, Joel. -Crow on solitaire

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