checking precision of a clock

Discussion in 'Clock Construction' started by dandydude, Sep 21, 2018.

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  1. dandydude

    dandydude Registered User

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    How did watchmakers test precision of a clock a few hundred years back? What did they check it against? How could they tell if a clock gained or lost a few seconds in a month/year? Not much of literature available covers this topic.

    Thanks
    Dandy
     
  2. John MacArthur

    John MacArthur Registered User
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    Harrison claimed that he'd sight across a particular mullion in a window and watch as a star passed behind his chimney. That way he thought he could tell the exact time within a second. This has been disputed by more recent astronomers as not quite that accurate. However, Harrison pulled off many seeming miracles, and it seems like that system would have been his most reliable until he moved to London. Most clockshops had a "regulator", presumably the owner's masterpiece, as the shop standard. The community could walk by, or ride up on their horses, and check the time on their watches by this. In London, the Greenwich observatory watched the stars with a large transit telescope, and could calculate the time easily within a second, and had a large ball on a mast that they would drop at noon every day, so that all the ships in harbor, as well as clockshops in the vicinity could check their regulators. I imagine there were observatories with their noon ball-drop associated with most major seaports, as timekeeping was so critical for the shipping industry. It's interesting to consider how clockmakers did stuff before technology that we take for granted came along.
    Johnny
     
  3. John MacArthur

    John MacArthur Registered User
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    Just read a note in Betts's wonderful chronometer book that the London clock and watchmaking district was far enough from Greenwich that periodically someone had to ride to Greenwich, set a good watch to exact time, and then ride back and set the shop regulator. We have a hard time even imagining this kind of thing.
    Johnny
     
  4. dandydude

    dandydude Registered User

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    Hello John,
    Thanks a lot for that piece of information. Wouldn't you have to sit in the exact same place, angle your head and eyes in the exact same way each time to watch the star passing the chimney? I mean if you needed to be precise.

    Thanks
    Dandy
     
  5. John MacArthur

    John MacArthur Registered User
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    Yes Dandy -- That's why a lot of people consider the story apocryphal. I should have said "fraction of a second", which is what he actually claimed, making it even less likely. His son inherited a star transit from him when he died, which says something.
    Johnny
     
  6. dandydude

    dandydude Registered User

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    Hi John,
    Thanks for your message. I don't know much about astronomy. I will have to study more.
    How doe we check precision of a clock today? With a microset, you can probably predict the error/accuracy. How do you check accuracy in terms of temperature or barometric compensation?

    Thanks
    Dandy
     
  7. Allan Wolff

    Allan Wolff Moderator
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  8. Phil Burman

    Phil Burman Registered User

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    Microset doesn't predict error/accuracy. What it does is compare the beat of you clock with a time standard, either an internal quartz clock of an optional external GPS signal. Microset also has an option for a atmospheric module together with optional software which provides for recording of temperature, pressure and humidity. This then allows you to compare the clock rate with the environmental changes.

    Phil
     
  9. Phil Burman

    Phil Burman Registered User

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    #9 Phil Burman, Sep 23, 2018
    Last edited: Sep 23, 2018
    Philip Woodwards' book "Woodward on Time" page 139 gives a description of a process called Least Squares Analysis which provides a means of comparing changes in rate with changes in temperature, pressure and arc, to give a correction coefficient for each.

    Phil
     
  10. John MacArthur

    John MacArthur Registered User
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    I have an analog clock app on my phone, and the second hand moves right with wwv. I'm not usually concerned with a minute fraction of a second any given day, I only worry if I've gained or lost several seconds over a week. I add or remove bb's from a thimble on top of the bob to bring it back to a rate.
    Johnny
     
  11. dandydude

    dandydude Registered User

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    Hi John,

    I am trying to target some serious accuracy. I may land flat on my face... but i just thought i will try. I currently only have temperature compensation built in. what did you mean by ' moves right with wwv'? Whats wwv?

    Thanks
    Dandy
     
  12. dandydude

    dandydude Registered User

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    Hi Phil,

    Thanks for your reply. I didn't know microset took atmospheric changes into consideration... Is it a separate piece of hardware that you need to be able to use the software?

    Thanks
    Dandy
     
  13. Phil Burman

    Phil Burman Registered User

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    Microset doesn't take atmospheric changes into consideration. Microset is a measuring device it doesn't perform any kind of analysis, The additional optional equipment provides measurement of other important parameters and the software allows the user to record and perform some manipulate of the measurements. Analysis it is up to the user according to his/her needs, hence my post #9.

    If you are serious about precision measurement then you need the following as a minimum:

    - MicroSet 3 Clock & Watch Timer
    - Atmospheric sensor (temperature, pressure, humidity)
    - Premium optical sensor
    - GPS Reference Receiver
    - Computer Interface (Windows based)
    - Universal AC adapter

    Phil
     
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  14. John MacArthur

    John MacArthur Registered User
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    It's what I think is called, in the British world, "time tick". In other words, the second hand on my app clock is within a small percentage of a second the exact time . Closer than that, I'm not worried about. I've enough on my plate trying to replicate the fine craft of the nineteenth century.
    Johnny
     
  15. Tim Orr

    Tim Orr National Membership Chair
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    Good afternoon, Dandy!

    WWV is one of the radio stations run by the National Institute of Standards and Technology (NIST) here in the USA. There are actually three radio stations, WWV, located near Ft. Collins, Colorado, on 2.5, 5, 10, 15, and 20 MHz, WWVH located in Hawaii, on similar frequencies, and WWVB, a low frequency (60 khz) station operating out of Ft. Collins. WWV and WWVH broadcast time and frequency signals, along with radio propagation reports and other information. WWVB broadcasts a time signal that is picked up and used by many of the so-called "atomic" or "radio-controlled" clocks that you can buy in the USA.

    These radio-synchronized clocks provide very high accuracy time for lots of people (according to NIST's own data, as of about 11 years ago, there were more than 50 million such clocks – and watches – and several million new ones were being added each year in the USA). Many collectors use these inexpensive time standards around the house to check the accuracy of the clocks and watches in our collections.

    There are both analog and digital versions of these clocks. For mechanical simplicity, some of the analog clocks are actually designed to run slightly fast. That way, when the time signal is received from WWVB, all the clock mechanism has to do is put the "brakes" on the clock slightly, to bring it back to sync. It would be far more mechanically complex to have to boost the speed momentarily to bring the clock into sync.

    Most of these clocks access the WWVB signal just once a day, often in the middle of the night. I am not knowledgeable about the Junghans "Mega" clock, but I believe I've been told that it uses the signal continuously. If the signal is not received, most of these clocks revert to being "free-running" quartz timepieces until such time as they can be synchronized, so they might drift a bit until that time. The Junghans clock, I am told, becomes useless without the WWVB signal.

    Besides these clocks, I understand that many other industrial uses of the WWVB signal control things like farm irrigation systems, etc.

    Unfortunately, there is a budget-cutting threat to NIST and these WWV, WWVH and WWVB services. See this thread: WWV Losing funding? What about our 'radio controlled watches and clocks?

    These little clocks are a tremendous convenience, and more important than we often think. There are (or were) similar systems in Britain, Germany and Japan. Not sure about India, or whether the Japanese signals reach all the way there.

    Best regards!

    Tim Orr
     
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  16. dandydude

    dandydude Registered User

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    Dear Tim,

    Thanks a ton for your elaborate reply. I will certainly look up if we get japanese wwv signals here.

    Thanks and regards
    Dandy
     
  17. dandydude

    dandydude Registered User

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    Hi Phil,

    Thanks for your reply. Are you aware of any online literature that talks about how to use these devices to achieve precision? I wish there were youtube videos explaining how to use all the precision testing gear.

    regards
    Dandy
     

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