Gents impulse clock

[Michael GilliganParticipant @michaelgilligan61133]

Posted by Bazyle on 16/06/2019 18:46:27:

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.

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But … the 'actual time' from GPS is not being used. The principle is to make use of the timebase [thoughtfully provided to make GPS function] to fine-tune the local oscillator.

As with metrology … The more accurate and stable the reference, the easier it is to obtain precise measurements.

MichaelG.

[Robert Atkinson 2Participant @robertatkinson2]

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

The PICTIC I linked to (corrupted by smiley) "http://www.ko4bb.com/doku2015/doku.php?id=precision_timingictic" Google KO4BB (O not zero) pictic to find it

is ideal for what you want. run it from a 10MHz OCXO and a optocoupler obscured every pendulum swing and it will send the time of every swing to a PC via the serial port.

Robert G8RPI.

[Robert Atkinson 2Participant @robertatkinson2]

Deleted

 

 

Edited By Robert Atkinson 2 on 16/06/2019 21:50:34

[Michael GilliganParticipant @michaelgilligan61133]

< I will try that again >

Edited By Michael Gilligan on 16/06/2019 21:59:01

[Michael GilliganParticipant @michaelgilligan61133]

< sorry, don't know what this forum is playing at >

Edited By Michael Gilligan on 16/06/2019 22:01:46

[Michael GilliganParticipant @michaelgilligan61133]

Thanks, Robert

Irritating little blighters, those smiley things !!

The link to PICTIC is on this page: **LINK**

http://www.ko4bb.com/doku2015/doku.php

… under 'Precision Timing'

MichaelG.

[Michael GilliganParticipant @michaelgilligan61133]

Posted by Robert Atkinson 2 on 16/06/2019 21:47:44:

… run it from a 10MHz OCXO and a optocoupler obscured every pendulum swing and it will send the time of every swing to a PC via the serial port.

Robert G8RPI.

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I think that's where we are probably on different interpretations, Robert

… I anticipate needing to use several measuring points; being more interested in the perturbations within a swing than in its overall duration

MichaelG.

[Robert Atkinson 2Participant @robertatkinson2]

Posted by Michael Gilligan on 16/06/2019 22:30:02:

Posted by Robert Atkinson 2 on 16/06/2019 21:47:44:

… run it from a 10MHz OCXO and a optocoupler obscured every pendulum swing and it will send the time of every swing to a PC via the serial port.

Robert G8RPI.

.

I think that's where we are probably on different interpretations, Robert

… I anticipate needing to use several measuring points; being more interested in the perturbations within a swing than in its overall duration

MichaelG.

that's more of a challenge as to how you capture the data without affecting the pendulum. A high frame rate camera and software would be one option. A more interesting one would be line CCD or diode array sensor like those used in document scanners sensing the shadow of the pendulum rod. This would give better resolution, easily 1024 positions, and require less processing. The sensor and lens from a flat bed scanner would probably work as is. Disconnect the sensor from the mechanical drive (initially leave that is as is for home and end sensors) and just try the scanning software. The image should be a sine wave.

I just realised I made a mistake on the OCXO accuracy. 31.5 seconds per year is 1×10^-6 if it all went out in the same direction at the beginning of the year. A more typical 1×10^-9 average is 0.03 seconds in a year.

Robert G8RPI.

[Michael GilliganParticipant @michaelgilligan61133]

Thanks, Robert …. I think we're on the same page now.

Probably best to pause for thought and let 'Plasma' have his thread back.

MichaelG.

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