Measuring the effect of unbalanced hands on a self winding clock.

Discussion in 'Electric Horology' started by lmester, Nov 15, 2014.

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  1. lmester

    lmester Registered User
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    Dec 30, 2009
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    I manage HVAC systems for a school district.
    West Virginia
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    I've noticed that the clock rate changes regularly on an hourly cycle. It appeared to be synchronized to the minute hand. I've noticed this on 400 day clocks. The rate varies significantly depending on whether the hand is going up or down. The self winding clock has much more power available but also has a large steel minute hand. I decided to verify that the unbalanced hand was the cause.

    I logged the clock rate and then attached a temporary counterweight to balance the hand.

    With the unbalanced hand the rate varies by about 40 microseconds.

    With the hand balanced the change was about 20 microseconds. The 20 microsecond change is synched to the clock winding. The clock speeds up when the spring is wound and gradually slows until the next winding.

    I actually found two things that affect the rate. The unbalanced hand and the amount of power available.

    First is a plot of the clock with the unbalanced hand.

    SWCCUb60f.png

    Next is the same data without any filter applied. The large spikes are caused by the clock winding.

    SWCCUbUf.png







    Here is with the balanced hand. The software that I'm using auto-scales the plot to fit the data. Notice that the scale has changed on these plots.

    SWCCBh60F.png

    And finally the same data without noise filtering. This allows you to see when the clock winds. You can see that the abrupt change in rate occurs when the clock winds.

    SWCCBhUf.png
     
  2. Tinker Dwight

    Tinker Dwight Registered User

    Oct 11, 2010
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    Most interesting Luke.
    First questions:
    Are you using an audio or optical pickup?
    How many uSec are in a day?
    Makes one what to go with a free pendulum.
    I'm assuming it has a typical deadbeat escapement.
    Tinker Dwight
     
  3. glenhead

    glenhead Registered User
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    Nov 15, 2009
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    86,400,000,000
     
  4. flynwill

    flynwill Registered User
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    Good answer, but probably not the answer Tinker was really seeking.....

    In this case Luke is measuring the period of the clock -- nominally 0.5 second if I read his graph correctly. So the 20 uSec change is 0.00002/0.5 = 0.004% change in rate which corresponds to an error of about 3.5 sec/day.
     
  5. lmester

    lmester Registered User
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    Dec 30, 2009
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    I manage HVAC systems for a school district.
    West Virginia
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    It's a Graham 1/2 second deadbeat.

    I'm using an infrared optical pickup.

    The x axis on the plot is in pendulum cycles. two beats per count.

    The rate changes due to hand position and spring winding are periodic. Probably not causing a large long term change.

    I'm still monitoring this clock. I've switched to a long period filter so that I can watch the rate change with temperature changes. The data is on my web page. You can check it online here. The plot will auto update every 30 seconds. This page probably won't win any awards for the most exciting web site :)
     
  6. praezis

    praezis Registered User

    Feb 11, 2008
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    By chance I dicovered the same effect just recently.
    Working on a project to synchronize a pendulum with DCF77 radio time, this 1-h-period wave appeared on my test diagrams:

    1411f1.gif

    To prove that it was the suspected minute hand, I just removed (fully balanced :D) it.
    This is what I got then:

    1411f2.gif

    The clock under test:

    IMG_0074bj.jpg

    Frank
     

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