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Gents impulse clock

How does it work

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Swarf, Mostly!14/06/2019 17:01:49
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Slightly off-topic because this thread is principally about Gents rather than Synchronome.

I was told by Barry (he of Barry's Virtual Clock Museum ) that the Kerplllunk emitted every 30 seconds by a Synchronome master clock installed in domestic premises has been known to sunder marriages!!!!!

Best regards,

Swarf, Mostly!

Plasma14/06/2019 20:57:18
337 forum posts
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Oh my word! What a wealth of information completely over my head lol.

You are one seriously clever guy SOD. I take my hat off to you.

Apologies for the photo orientation but this is the clock I wondered if was a master for the gents skace clock?

Staff though it was some kind of time recording clock or clocking in machine but I'm not sure.

20190614_173837.jpg

Plasma14/06/2019 20:58:03
337 forum posts
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Or am I looking for something different? This was thrown in one of the cellars!

Michael Gilligan14/06/2019 21:13:17
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Posted by Plasma on 14/06/2019 20:57:18:

Apologies for the photo orientation but this is the clock I wondered if was a master for the gents skace clock?

Staff though it was some kind of time recording clock or clocking in machine but I'm not sure.

.

That looks very much like one that I have

... easy to confirm if you can post a picture of the innards

MichaelG.

Plasma14/06/2019 21:28:46
337 forum posts
41 photos

Door was locked but took an up skirt of the mechanism....20190614_173918.jpg

Robert Atkinson 214/06/2019 21:54:40
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Yes, that is a master clock. Nice find.

Robert G8RPI.

Michael Gilligan14/06/2019 21:54:50
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surprise

blush

Yes that looks right ...

Text at the bottom of the casting should read PUL-SYN-ETIC

MichaelG.

.

Here 'tis ...

img_3062.jpg

Edited By Michael Gilligan on 14/06/2019 22:02:09

Robert Atkinson 214/06/2019 22:02:39
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Posted by Michael Gilligan on 13/06/2019 16:51:09:
Posted by Frances IoM on 13/06/2019 16:24:11:
why not just extract the mechanism from a radio controlled clock or even the many GPS rcvrs that push out the time accurate to microseconds!

.

Which reminds me of a round tuit ... I have most of the parts to build something like this:

**LINK**

http://www.jrmiller.demon.co.uk/projects/freqstd/frqstd.htm

MichaelG.

You don't need the extra oscillator and phase locking for a master clock, just a divide by 30 on the 1pps output (an a flipflop to reverse the polarity every other pulse for a Gents. If you want to build a Miller style GPSDO you need one of the Jupiter receivers with a 10kHz output. I've got a couple if you are stuck. Andy G4JNT has some good info too.

Robert G8RPI.

Michael Gilligan14/06/2019 22:36:22
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Posted by Robert Atkinson 2 on 14/06/2019 22:02:39:
... If you want to build a Miller style GPSDO you need one of the Jupiter receivers with a 10kHz output. I've got a couple if you are stuck.

.

Thanks, Robert ... but yes, I have a Jupiter receiver.

The GPSDO will [hopefully, one day] be for checking the performance of pendulums rather than for driving anything.

MichaelG.

SillyOldDuffer15/06/2019 09:57:56
4713 forum posts
1010 photos
Posted by Michael Gilligan on 14/06/2019 22:36:22:
Posted by Robert Atkinson 2 on 14/06/2019 22:02:39:
 
... If you want to build a Miller style GPSDO you need one of the Jupiter receivers with a 10kHz output. I've got a couple if you are stuck.

.

Thanks, Robert ... but yes, I have a Jupiter receiver.

The GPSDO will [hopefully, one day] be for checking the performance of pendulums rather than for driving anything.

MichaelG.

I've got a stalled Arduino 'Clock Analyser' project due to not solving the accurate clock problem!

My clock analyser compares pendulum swing times to a high accuracy clock at microsecond levels, which reveals all sorts of interesting effects, like vibration due to people walking nearby. It also logs performance data over long periods with temperature, humidity and air pressure in hope of linking misbehaviour to environmental changes. It's intended to be portable, so that pendulum clocks can be tested without moving them.

GPS is an excellent time source with the better modules accurate to within a few nanoseconds of International Atomic Time. All GPS modules output printable date-time strings but these will be several milliseconds wrong due to the time it takes to process and display them. Fortunately, some GPS module also produce accurate seconds pulses, making it possible to closely synchronise display time to atomic time.

On my dining table everything works a treat. Downfall! The GPS unit only works properly when its antenna has clear view of the sky. Likely this isn't possible when the test clock is inside a house. Same objection to the time standards broadcast by long-wave radio, with the additional problem that receivers are hard to buy without paying for a whole clock.  Broken into, the receiver may be an electronic mystery.

Using the analyser on a real test pendulum was 'Quite Interesting'. It seems that the precise timing of individual pendulum swings vary slightly but the errors mostly cancel out. Provided the errors cancel, an imperfect pendulum can still keep good time. For that reason, perhaps an ultra-accurate pendulum analyser isn't as useful as I imagined. Oh dear...

Dave

 

Edited By SillyOldDuffer on 15/06/2019 10:00:49

John Haine15/06/2019 10:46:20
2608 forum posts
133 photos

Dave, the errors don't cancel, quite. They add up as a sort of "drunkard's walk" depending on the type of disturbance and the Q of the pendulum.

John Haine15/06/2019 10:49:51
2608 forum posts
133 photos
Posted by Swarf, Mostly! on 14/06/2019 17:01:49:

Slightly off-topic because this thread is principally about Gents rather than Synchronome.

I was told by Barry (he of Barry's Virtual Clock Museum ) that the Kerplllunk emitted every 30 seconds by a Synchronome master clock installed in domestic premises has been known to sunder marriages!!!!!

Best regards,

Swarf, Mostly!

Indeed, one of the reasons why my re-build of a Synchronome resets the gravity arm with a little stepper motor and uses another stepper to drive the hands, replacing the electromagnet in the slave clock. An Arduino controls the steppers sensing the pendulum with an opto coupler. Some teething problems, but nearly going.

Michael Gilligan15/06/2019 13:42:10
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14014 forum posts
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Posted by SillyOldDuffer on 15/06/2019 09:57:56:
.
I've got a stalled Arduino 'Clock Analyser' project due to not solving the accurate clock problem! [ ... ]
 

 

.

Dave

I think you have just made an excellent 'business case' justification for the GPSDO

Using GPS to 'discipline' an [already good] oven-stabiised Crystal Oscillator, is probably the most cost-effective way you will ever find of obtaining a reliable reference signal.

MichaelG.

Edited By Michael Gilligan on 15/06/2019 13:45:15

Robert Atkinson 215/06/2019 19:24:05
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367 forum posts
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For clock setting you don't need a full GPSDO. Just get a Oven Controlled Crystal Oscillator (OCXO) or Temperature Compensated Crystal Oscillator (TCXO) with adjust ment and set it occasionally aginst a GPS. This is easy if you have an oscilloscope. Trigger the 'scope from the GPS 1PPS output (e.g.) put it on channel one) and monitor the output of the oscillator on one channel. The trace of the oscillator will drift across the screen. adjust it for minimum drift and it will be accurate to fractions of parts per million. you can then put the GPS away for 6 months. or more. This assumes it was already within 1Hz of nominal frequency.

Lots of OCXOs and TCXOs on ebay.

Robert G8RPI. (time nut, 5 GPSDO's, 4 Rubidium atomic frequency standards, HP 5370B etc).

Neil Wyatt15/06/2019 19:46:55
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Posted by SillyOldDuffer on 15/06/2019 09:57:56:

GPS is an excellent time source with the better modules accurate to within a few nanoseconds of International Atomic Time. All GPS modules output printable date-time strings but these will be several milliseconds wrong due to the time it takes to process and display them. Fortunately, some GPS module also produce accurate seconds pulses, making it possible to closely synchronise display time to atomic time.

A good excuse to use a basic microcontroller, you can disable interrupts and write deterministic code to read the gps data and output it with a constant and calculable lag.

Neil

SillyOldDuffer15/06/2019 21:32:18
4713 forum posts
1010 photos
Posted by Neil Wyatt on 15/06/2019 19:46:55:
Posted by SillyOldDuffer on 15/06/2019 09:57:56:

GPS is an excellent time source with the better modules accurate to within a few nanoseconds of International Atomic Time. All GPS modules output printable date-time strings but these will be several milliseconds wrong due to the time it takes to process and display them. Fortunately, some GPS module also produce accurate seconds pulses, making it possible to closely synchronise display time to atomic time.

A good excuse to use a basic microcontroller, you can disable interrupts and write deterministic code to read the gps data and output it with a constant and calculable lag.

Neil

Or the other way round.

After the GPS has got a satellite lock, wait for it to send a timestamped navigational fix over the slow serial link. Use the timestamp set a 'clock' in the microcontroller. This time is correct to the last second but offset by a small processing delay, several tens of milliseconds.

However, although GPS timestamps aren't spot on, the GPS emits hardware second pulses that are. By connecting them to an interrupt pin, the micro-controller's 'clock' can be ticked once per second by the GPS, keeping the microcontroller very close to GPS time. It's wrong by however long it takes to process the interrupt, perhaps a few microseconds.

Not sure this is the best strategy but it seems to work.

Dave

Michael Gilligan15/06/2019 22:25:54
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Posted by Robert Atkinson 2 on 15/06/2019 19:24:05:

For clock setting you don't need a full GPSDO. Just get ... etc.

.

With the greatest respect, Robert

[and a man with 5 GPSDO's, 4 Rubidium atomic frequency standards, HP 5370B etc. surely deserves that]

My interest is more to do with studying the stability of a pendulum than setting its rate

and I would have more confidence in my results if the crystal oscillator was 'disciplined'

Please feel free to put me right [publicly or privately] if I have this wrong ... I am a mere dabbler.

MichaelG.

duncan webster16/06/2019 12:10:26
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Posted by John Haine on 15/06/2019 10:49:51:
Posted by Swarf, Mostly! on 14/06/2019 17:01:49:

Indeed, one of the reasons why my re-build of a Synchronome resets the gravity arm with a little stepper motor and uses another stepper to drive the hands, replacing the electromagnet in the slave clock. An Arduino controls the steppers sensing the pendulum with an opto coupler. Some teething problems, but nearly going.

I trust you are going to write this up for ME, avoiding the 30 second 'earthquake' on resetting the gravity arm was one factor in deciding on electro-magnet drive for the pendulum on my clock.

Michael Gilligan16/06/2019 13:24:54
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Posted by duncan webster on 16/06/2019 12:10:26:

I trust you are going to write this up for ME.

.

Just wondering, Duncan

Is that because you subscribe to ME, or do you see a precedent ?

... Horological Journal seems a reasonable contender.

MichaelG.

.

P.S. I acknowledge that FHJ was very supportive of amateur constructors.

Edited By Michael Gilligan on 16/06/2019 13:29:10

John Haine16/06/2019 13:58:01
2608 forum posts
133 photos

As the clock is a bit of a "Topsy", there aren't really nice drawings for a constructor to follow I'm afraid. I have wondered about a more "this is what I did" type article for HJ.

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