[time-nuts] Shortt Clock Recent Measurements

Don Latham djl at montana.com
Tue Dec 10 20:57:31 EST 2013



> I always thought invar was the magic metal. Quartz rod? You can get
> those
> at some reasonable cost?
12 mm dia fused qtz, about $10 per ft, so under $40 to get going,
assuming 4 or 5 to learn how to do it right. It does break...
12.7 mm dia Invar 1 m long is $530   Amazing, and quartz is better (A
single crystal would cost a pretty penny. I'm not sure a crystal that
long can be drawn using a zone furnace). Pyrex is also available.
These are quick 'net prices.


> What I am curious about is there a wear mechanism on these really good
> clocks.
> Does the pendulum just swing on a bending piece of metal or on a
> bearing?

most on bending metal. The 100 lb weight Foucault pendulum at Griffith
Observatory that I liked as a kid, 65 yr ago, simply had a piano wire
chucked in a pin vise. Lasted until now, AFIK.
Qtz rod would require some kind of epoxied cap etc. There are also knife
edge bearings and the like. The Q of the pendulum depends in part on the
energy lost in the support "hinge". OTH, some energy has to be lost in
order to quell possible chaotic modes (that's my opinion and I'm
stickin' to it)

> To the technical side isn't it sort of cheating the wonder of the clock
> using gps correction.
Yep.

I mean at that point there is no point.
> I am asking these questions because its sort of the thing I would not
> mind
> crafting.
> Regards
> Paul.
> WB8TSL
>
>
> On Tue, Dec 10, 2013 at 7:15 PM, Don Latham <djl at montana.com> wrote:
>
>> Brian and Tom: I second as well. It's important to be aware of the
>> past.
>> Somewhere around here is a 4 ft length of Invar, 1/2 in. diameter. It
>> was supposed to be a pendulum rod. However, I did read that Invar
>> displays rearrangement noise of some kind. Kinda like the jumps in a
>> quartz element?
>> I think if I were to start designing, I'd use a quartz rod instead,
>> coefficient of thermal expansion is smaller. I'll bet that a large
>> majority of time-nuts have at least read about pendulum timekeepers...
>> The Smithsonian has a Schortt clock, as well as a couple of others. I
>> am
>> sad that they aren't running.
>> Don
>>
>> Brian, WA1ZMS
>> > FWIW....
>> >
>> > Let me just second Tom's last comment:
>> > "Some of you readers might wonder why in this GPS age, two time
>> nuts,
>> > each
>> > with plenty of atomic clocks at home, would be talking about vintage
>> > pendulum clocks. It turns out that pendulum clocks are still
>> extremely
>> > interesting timekeepers, from an experimental, scientific, and
>> > historical
>> > perspective."
>> >
>> > About 2 years ago the Time Nut in me became very interested in
>> pendulum
>> > clocks that were made in my home town in Vermont going back as far
>> as
>> > 1797.
>> > I now own several and a project is to take one of them that has a
>> > dead-beat
>> > escapement (often noted for its better "accuracy" display of seconds
>> > with an
>> > 10 inch sweep hand in its day) into the 21st century with frequency
>> > locking
>> > of the pendulum to the 1PPS from one of my GPS receivers.
>> >
>> > Also....An antique clock dealer who is friend of mine was well
>> pleased
>> > with
>> > TVB's talk at a recent time conference on the West Coast.  So it is
>> a
>> > mix of
>> > old and new for me at this point.   Apologies if this goes OT.
>> >
>> > Regards,
>> > -Brian, WA1ZMS/4
>> >
>> >
>> > -----Original Message-----
>> > From: time-nuts-bounces at febo.com [mailto:time-nuts-bounces at febo.com]
>> On
>> > Behalf Of Tom Van Baak
>> > Sent: Tuesday, December 10, 2013 5:48 PM
>> > To: Discussion of precise time and frequency measurement
>> > Subject: Re: [time-nuts] Shortt Clock Recent Measurements
>> >
>> >> The Wiki page for the Shortt pendulum clock has a "Recent
>> >> Measurements"
>> > (1984)  paragraph that's in error.
>> >> http://en.wikipedia.org/wiki/Shortt-Synchronome_clock#Recent_accuracy_
>> >> measurement
>> >>
>> >> While it's probably true that the clock is stable to 200 uS per day
>> >> (i.e. 2E-9) I believe Alfred Loomis discovered the effect of the
>> moon
>> >> on
>> > this clock a long time ago.
>> >
>> > Hi Brooke,
>> >
>> > The wiki page is correct. The heading is "Recent Measurements" and
>> > Pierre
>> > Boucheron's 1984 effort certainly qualifies. Note the wiki doesn't
>> claim
>> > Boucheron was the first. In fact, even 30 years old, it is still the
>> > most
>> > recent, and the only Shortt experiment for which we have raw data.
>> See
>> > http://leapsecond.com/pend/shortt/ for details.
>> >
>> > One could try claiming that Loomis was the first to make detailed
>> > measurements of a Shortt, but it would take some digging to prove he
>> was
>> > "first" and not just "one of the first". I mean, if you look at the
>> list
>> > of
>> > who received the one hundred Shortt's that were manufactured, many
>> > laboratories had more than one, not to mention the ones that William
>> > Shortt
>> > himself owned at the factory. Certainly there was a lot of time
>> > measurement
>> > going on in the 20's and 30's. It would take a lot of work to
>> uncover
>> > what
>> > was known by whom and when. Or who published first or not.
>> >
>> > I think Loomis took it a wonderful extreme with his spark
>> chronograph
>> > and
>> > quartz oscillator via telephone time transfer setup. And that be
>> bought
>> > three clocks at once is classic and inspiring to any time nut! So I
>> > agree,
>> > Loomis deserves mention on the Shortt wiki page.
>> >
>> > Unrelated to gravity and tides, is the role that vacuum pendulum and
>> > ovenized quartz clocks had in confirming that earth rotation was
>> itself
>> > irregular at the millisecond level. Credit for that usually goes to
>> > Scheibe
>> > and Adelsberger in the late 30's, not Shortt or Loomis. And that of
>> > course
>> > blends into the story of the leap second...
>> >
>> > See my scan/OCR historical pendulum collection:
>> > http://leapsecond.com/pend/pdf/ And my own precision pendulum-nut
>> > articles:
>> > http://leapsecond.com/hsn2006/
>> >
>> > Some of you readers might wonder why in this GPS age, two time nuts,
>> > each
>> > with plenty of atomic clocks at home, would be talking about vintage
>> > pendulum clocks. It turns out that pendulum clocks are still
>> extremely
>> > interesting timekeepers, from an experimental, scientific, and
>> > historical
>> > perspective.
>> >
>> > /tvb
>> >
>> >
>> > _______________________________________________
>> > time-nuts mailing list -- time-nuts at febo.com To unsubscribe, go to
>> > https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
>> > and follow the instructions there.
>> >
>> > _______________________________________________
>> > time-nuts mailing list -- time-nuts at febo.com
>> > To unsubscribe, go to
>> > https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
>> > and follow the instructions there.
>> >
>> >
>>
>>
>> --
>> "The power of accurate observation is commonly called cynicism by
>> those
>> who have not got it."
>>  -George Bernard Shaw
>>
>>
>> Dr. Don Latham AJ7LL
>> Six Mile Systems LLC
>> 17850 Six Mile Road
>> POB 134
>> Huson, MT, 59846
>> VOX 406-626-4304
>> Skype: buffler2
>> www.lightningforensics.com
>> www.sixmilesystems.com
>>
>>
>> _______________________________________________
>> time-nuts mailing list -- time-nuts at febo.com
>> To unsubscribe, go to
>> https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
>> and follow the instructions there.
>>
> _______________________________________________
> time-nuts mailing list -- time-nuts at febo.com
> To unsubscribe, go to
> https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
> and follow the instructions there.
>
>


-- 
"The power of accurate observation is commonly called cynicism by those
who have not got it."
 -George Bernard Shaw


Dr. Don Latham AJ7LL
Six Mile Systems LLC
17850 Six Mile Road
POB 134
Huson, MT, 59846
VOX 406-626-4304
Skype: buffler2
www.lightningforensics.com
www.sixmilesystems.com




More information about the time-nuts mailing list