pendulum swing amplitude question

rogerj

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Dec 21, 2014
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I've built (another) electrically impulsed clock with a 1 sec pendulum. Originally it was a British Post Office clock type 36 and now makes use of the case, the chassis board and drive coil and the Invar pendulum road. The bob ihowever is bigger and heavier - like a Synchronome bob.
The pendulum amplitude is 0.5 inches (1 inch side to side). It is sensed optically so is very close to being "free" and is impulsed by electro-magnet once per minute.
Only the suspension spring offers mechanical interference, so air drag, air viscosity and barometric pressure variations seem to be the main sources of error.

The construction method would easily allow the amplitude to be halved or perhaps made even less - perhaps even down to 1/4" total. So, the question Is, is there any likelihood of improved rate stability with VERY small arcs ?
 

rogerj

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So nobody has any theories on small or large arcs.. Either you've decided I'm crazy or everyone is a John Harrison devotee :) In filming this short video I've noticed the arc has crept up a little to just over 1" but it shows the sensor and the "count wheel"
 

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Tim Orr

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Good evening, Roger!

Perhaps you've already tried them, but there is, in my view, an incredibly knowledgeable group of British electric clock enthusiasts at another message board. You could post your question, I believe, at electric-clocks@groups.io

You can contact the list owner at: electric-clocks+owner@groups.io

Based on what I have seen, you should be able to find someone who can help answer your question. I suspect the lack of response you've experienced here has more to do with limited knowledge than limited interest.

Received wisdom, of course, is that the smaller the arc the better – by minimizing circular error – but it does not come without a cost in other areas.

Best regards!

Tim Orr
 

bruce linde

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tinker dwight would have had an answer from the math side of the equation, but hasn't been around in a while..... let us know what you find out.
 

rogerj

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Good evening, Roger!

"peceived wisdom, of course, is that the smaller the arc the better – by minimizing circular error – but it does not come without a cost in other areas.

Best regards!

Tim Orr
Thanks Tim and Bruce. It's been a while since I posted here and do remember that TD would have probably been quick to respond on something like this I. hope he is OK.
It's the " but it does not come without a cost in other areas" part that I'm keen to hear about.. I do know about the other forums and may consider asking there.. I have only just finished regulating the clock and have been lucky to have just had 48 hrs of steady barometric pressure. But my friend Mike (to whom I am indebted to for the Raspberry Pi monitoring software ) suspects other factors - like humidty, and thinner air with rising temp - all affect the rate, but so far we have not tied it down. The attached graph for the last 48 hours shows the rate achieved right now. Centre line is GMT, scale is +/- 1 sec.. the last recorded offset was 38 millisecs.. Not bad for a very simple Pendulum clock ? 1.07.21.png
Regards.. Roger
 

praezis

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Hi,
lower amplitude has the advantage that a certain amplitude variation will have less impact on the rate (limited by the point where movement can be detected at all and its accuracy).
And - the lower the amplitude, the shorter the portion of free swing of the pendulum, unaffected by the driving pulse that cannot be infinite short.
I don't know your setup. If you control and stabilize the amplitude, all the better.

Very important is a driving pulse symmetrical to the rest position of the pendulum.

Frank
 
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rogerj

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Hi,
lower amplitude has the advantage that a certain amplitude variation will have less impact on the rate (limited by the point where movement can be detected at all and its accuracy).
And - the lower the amplitude, the shorter the portion of free swing of the pendulum, unaffected by the driving pulse that cannot be infinite short.
I don't know your setup. If you control and stabilize the amplitude, all the better.

Very important is a driving pulse symmetrical to the rest position of the pendulum.

Frank
The setup is described fully here: A DIY, NON Hipp Toggle master clock. With offset sensor I haven't been able to get it to run reliably below 1" swing. But I've an idea involving placing the sensor centrally which does mean making more electronics to get the drive impulse central. After monitoring it, as is for a little longer, I will try it anyway..
 

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