Gents impulse clock

[PlasmaParticipant @plasma]

Door was locked but took an up skirt of the mechanism….

[Robert Atkinson 2Participant @robertatkinson2]

Yes, that is a master clock. Nice find.

Robert G8RPI.

[Michael GilliganParticipant @michaelgilligan61133]

Yes that looks right …

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

MichaelG.

.

Here 'tis …

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

[Robert Atkinson 2Participant @robertatkinson2]

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 GilliganParticipant @michaelgilligan61133]

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.

[SillyOldDufferModerator @sillyoldduffer]

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 HaineParticipant @johnhaine32865]

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 HaineParticipant @johnhaine32865]

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 GilliganParticipant @michaelgilligan61133]

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 2Participant @robertatkinson2]

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 WyattModerator @neilwyatt]

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

[SillyOldDufferModerator @sillyoldduffer]

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 GilliganParticipant @michaelgilligan61133]

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 webster 1Participant @duncanwebster1]

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 GilliganParticipant @michaelgilligan61133]

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 HaineParticipant @johnhaine32865]

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.

[SillyOldDufferModerator @sillyoldduffer]

Posted by Michael Gilligan on 15/06/2019 13:42:10:

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.

Alas, Business Case fails on cost. I found a few GPSDO modules for sale at about £100 each. Would be possible to make one cheaper except a design goal was a high-end Clock Analyser that anyone could replicate with cheap readily available modules. Plug and play rather than grown-up electronics.

Wondering now about using a Wireless technology such as Bluetooth to link a GPS unit in the clear to the analyser-part indoors next to the pendulum. Unfortunately, although the radio link is quick ( say 0.1µS delay over 30 metres), encoding and decoding Bluetooth messages isn't. And a wireless link is more cost and complexity.

Very tempted to steal Robert's collection of Rubidium Oscillators, drool…

John's drunkards walk comment has me thinking too. It reinforces my original notion that a pendulum analyser needs to be able to see both micro-variations in time keeping and subtle long term effects.

My test pendulum may be misleadingly good in the sense it's not a realistic mechanical clock, hence me not seeing a drunkards walk during testing. It's a steel bob on a carbon-fibre thread energised by an optically triggered weak electromagnet. I suppose because the mechanical and temperature effects on the pendulum are low, it keeps remarkably good time. Better than 20ppm when running well and I got one run of 8ppm. This with the bob dangling from a wobbly Meccano gantry.

So good was the test pendulums performance, I've toyed with the idea of a properly engineered rigid frame mounted inside a length of 4" plastic drainpipe from which most of the air has been removed. I think a simple arrangement like that would outperform all but the best mechanical clocks, essentially by dodging the friction and impulse problems that make building accurate mechanical clocks seriously challenging.

Not quite as attractive as a well-made brass clock. I doubt anyone would admire 18" of old sewage pipe perched on my mantelpiece…

Dave

[Michael GilliganParticipant @michaelgilligan61133]

Posted by SillyOldDuffer on 16/06/2019 14:26:54:

Posted by Michael Gilligan on 15/06/2019 13:42:10:

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.

Alas, Business Case fails on cost. I found a few GPSDO modules for sale at about £100 each.

.

Point taken … although I'm pretty sure that my [incomplete] collection of components includes all the clever bits, and has cost me much less than £100 so far.

… It might, however, be embarrassing to check how much, and how long it has taken to accumulate them

If it's any help; I have just rediscovered James Miller's simplified design: **LINK**

http://www.jrmiller.demon.co.uk/projects/ministd/frqstd0.htm

MichaelG.

[Robert Atkinson 2Participant @robertatkinson2]

Posted by Michael Gilligan on 15/06/2019 22:25:54:

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.

Any decent OCXO will be accurate to 1 part per million in a year (<1×10^6, HP's 10811A is more than 10 times better than that) so that's 31 seconds in a year worst case. Over shorter time scales eg days it's typically a thousand times better so 0.001 seconds per day. How good do you need?

Robert G8RPI.

[Robert Atkinson 2Participant @robertatkinson2]

For a lowcost time interval counter with logging on a pc for checking clocks etc see

http://www.ko4bb.com/doku2015/doku.php?id=precision_timingictic

Robert G8RPI

[John HaineParticipant @johnhaine32865]

Hmmm…that link doesn't work very well with an emoji in it Robert! Please could you try again?

[Michael GilliganParticipant @michaelgilligan61133]

Posted by Robert Atkinson 2 on 16/06/2019 15:27:06:

… How good do you need?

Robert G8RPI.

.

I honestly don't know, Robert … that's the problem

Not that I aspire to replicating one : The Shortt observatory clocks were thought to be accurate to about one second per year, but recent tests suggested that one second in twelve years might be nearer the truth !!

What I'm really interested in though is the shorter-term stability, and response to external stimuli, of a somewhat more practical pendulum than that.

MichaelG.

[SillyOldDufferModerator @sillyoldduffer]

Posted by Michael Gilligan on 16/06/2019 16:03:41:

Posted by Robert Atkinson 2 on 16/06/2019 15:27:06:

… How good do you need?

Robert G8RPI.

.

I honestly don't know, Robert … that's the problem

…

What I'm really interested in though is the shorter-term stability, and response to external stimuli, of a somewhat more practical pendulum than that.

MichaelG.

Michael and I are interested in the behaviour of individual pendulum swings where averaging hides useful detail. The easiest way (I think) is to compare the test pendulum with a much more accurate clock, and the more accurate the better.

With a pendulum clock, tens of microseconds are interesting, and picosecond resolution would be even more revealing. It's a bit like measuring length: to measure a thou accurately, you need an instrument that can get close to tenths.

Looking closely at the timing of a pendulum shows clock faults, for example I think I can detect the difference between a pendulum swinging true and one following an ellipse. On my test rig an elliptical swing has more jitter, I'm not sure why. I suspect it's due to a combination of the impulse being misplaced relative to the bob, torsion in the rod, and maybe bending at the pivot.

Dave

[Michael GilliganParticipant @michaelgilligan61133]

Thanks, Dave … We're definitely on the same wavelength

Incidentally, my Jupiter GPS module was a few more £s than I remembered

The OCXO though was £16 from ebay [new old stock in 2007]

… probably totally obsolete by now !!

MichaelG.

[BazyleParticipant @bazyle]

As mentioned by Robert I can't see how the actual time, from GPS, matters when you can get a local clock that has high stability in the time period you are measuring, and if it is drifting you can measure over an extended period and compensate.

I think you would find it more instructive to be able to measure the actual physical position of the pendulum hundreds of times per swing to compare swings to see the difference made by the application of the impulse, especially when mechanically impulsed.

[Author]

Posts