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  1. #31

    Default Re: Bob temperature compensation (By: Tinker Dwight)

    Hi Tinker..
    The Pi software was designed for a Synchronome so expects a pulse every 30 secs. I added a /30 in hardware to make it work with mine..Every 30 seconds it records a time-stamp from a NTP time server on the net..
    I tried to word it so it didn't look like you needed to look up how a Hipp Toggle works ! But I don't think I succeeded.
    If you do Google "Hipp Toggle" it will be the first hit..Don't know why Google thinks it's the most relevant source of info out there....
    There is a full description with my simple circuit diagrams...
    Originally I timed it to 30 seconds but recently removed some resistance from in series with the impulse magnet (that was easy to get at without stopping the clock) and it went to 52..Sometime I'll try adjusting it to 60 seconds
    Roger

  2. #32
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    Default Re: Bob temperature compensation (By: rogerj)

    Quote Originally Posted by rogerj View Post
    Hi Tinker..
    The Pi software was designed for a Synchronome so expects a pulse every 30 secs. I added a /30 in hardware to make it work with mine..Every 30 seconds it records a time-stamp from a NTP time server on the net..
    I tried to word it so it didn't look like you needed to look up how a Hipp Toggle works ! But I don't think I succeeded.
    If you do Google "Hipp Toggle" it will be the first hit..Don't know why Google thinks it's the most relevant source of info out there....
    There is a full description with my simple circuit diagrams...
    Originally I timed it to 30 seconds but recently removed some resistance from in series with the impulse magnet (that was easy to get at without stopping the clock) and it went to 52..Sometime I'll try adjusting it to 60 seconds
    Roger
    What clock source are you using as a reference?
    It isn't a problem of software, it is a problem of reference used
    that I'm asking.
    Tinker Dwight

  3. #33

    Default Re: Bob temperature compensation (By: Tinker Dwight)

    Every 30 seconds the software is triggered to see what the offset error is between the pulse and the time off an NTP server. A value in milliseconds is recorded. The average error over every 5 min period goes to the graph..Does that make sense ? Roger

  4. #34
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    Default Re: Bob temperature compensation (By: rogerj)

    Quote Originally Posted by rogerj View Post
    Every 30 seconds the software is triggered to see what the offset error is between the pulse and the time off an NTP server. A value in milliseconds is recorded. The average error over every 5 min period goes to the graph..Does that make sense ? Roger

    I doubt the server is providing an accurate time standard to the level you need.
    The best you can use is either a temperature compensated quartz oscillator
    or a GPS that has a one second time pulse out.
    Your server shouldn't have any long term drift but I wouldn't rely on it for
    sub millisecond timing.
    Unless you want to see some other funny aliasing you might want to set
    the power pulses to an prime number, not near 30 or 60.
    Are you using a true mechanical switch or an optical interrupter
    for the Hipp Toggle?
    Tinker Dwight
    Last edited by Tinker Dwight; 04-19-2017 at 04:40 PM.

  5. #35

    Default Re: Bob temperature compensation

    Hi Tinker.
    In reverse order..yes I am using an optical interrupter as the Hipp detector.
    Next time I alter the impulse period I will try for 59....but I wish I understood the reason !
    On the 17th Mar I asked my friend to send me a graph of the un-averaged raw data over a short period..Here' a short sample of the going showing what we think are the small cyclic circular errors, albeit samples of a 52 sec period wave sampled every 30 secs.


    I'm not knowledgeable enough to debate the accuracy of an NTP server but I have discussed it with my friend who had thought of the possibility of short term jitter from the internet route and the WiFi to the Pi. I believe that's why he had decided on taken a 5 minute average of the previous 30 second samples. As for the long term accuracy we had never doubted it...I'd be interested in knowing why you question it..Certainly his Synchronome or my DIY clock are ever going to break any records..Roger
    Attached Thumbnails Attached Thumbnails aaa raw data.png  

  6. #36
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    Default Re: Bob temperature compensation (By: rogerj)

    Most computers only need to check the time once a minute.
    The build in time reverence is the over driven crystal used for the
    processor speed.
    Then they use an estimated error from a two way path over the
    net.
    They are usually within a second of the correct time but usually
    as much as 5-10 milliseconds fast or slow every minute.
    Some of the variation you see is likely from such differences.
    The daily drift rate is real but some of the ups and downs may just
    be the processor responding to its drift and variability.
    In the graph you're showing the short term are likely your pendulum
    but the general waviness may not be.
    Using an prime number of swings will shorten the time of sampling error
    caused by beating against the reference frequency. It ensures that you
    don't have something like a 1 hour beat in the sampling method and seeing
    it as some error in your pendulum. I might choose something like 53 swings.
    If you used something like 60 and the computer was correcting on 60 seconds
    the beat frequency might be hours that you see as long term drift in your
    pendulum. It might actually just be systematic errors in some part of the
    sampling noise.
    An interesting thing to do is to save all the samples and do an FFT on the data.
    Decimate the data at different amount and again run a FFT. This will allow
    you to see the different types of regular noise. These will usually show up
    as peaks at regular points. Your pulse rate of the pendulum should be clear
    but other errors can be hiding.
    Tinker Dwight

  7. #37

    Default Re: Bob temperature compensation (By: Tinker Dwight)

    Thanks for that insight..I will pass your info to my friend to see what he makes of it..
    As my clock outputs 1 pps and is divided by 30 in an external board, it would be possible to test the sytem by substituting 1 pps from a GPS receiver (which I already have) Roger

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