Connect with us

How does this work?

Discussion in 'Electronic Design' started by Anthony Fremont, Jun 30, 2006.

Scroll to continue with content
  1. Being an amateur horologist/PIC-hacker that lives on a tight budget,
    I've glommed together my own version of the professional clock/watch
    timing equipment. I have optical, acoustical and inductive sensor
    inputs. Using a PC and some Visual Basic coding, I can duplicate
    virtually all the functionality of these highly expensive machines.
    Everything is fine except for one minor issue. The professional watch
    timing machines purport being able to determine the amplitude of a
    balance wheel's swing. They manage to do this by purely acoustical
    sensing methods. :-? :-? :-? :-?

    For the life of me, I can't figure a way to listen to watch ticking
    sounds and determine the arc of the balance wheel. These watch timing
    machines have been doing this for decades, how? The interval between
    the roller jewel smacking the lever aint it, that just determines the
    rate (beats per hour) and the amount of beat error. When the balance
    wheel stops and reverses, there is no sound created by that event. Any
    ideas?
     
  2. How about this (random thought). Try to think about it in exaggerated
    terms. Suppose that the swing is very heavy. Make watch float in
    liquid (say on a little piece of styrofoam).

    Then rotations of the swing would cause watch to "recoil" in the
    opposite direction. Since you know the weight and momentum of inertia
    of the watch, you could figure out a lot about the swing if you can
    measure the watch's recoil.

    i
     
  3. Luhan

    Luhan Guest


    Could you post a link to the company making these claims?

    Luhan
     
  4. Might acoustical sensing include doppler sensing of the maximum
    velocity of the wheel? If it's simple harmonic motion, you would have
    amplitude = vmax / angular frequency.
     
  5. It's done entirely acoustically, but the calculation involves the
    "lift angle", which must be entered manually for a given movement.


    Best regards,
    Spehro Pefhany
     
  6. Nonnymus

    Nonnymus Guest

    X-No-archive: yes

    Elegant and practical way to do it. Actually, there would
    be no need for calculations; all you would have to do would
    be to watch and make adjustments until no rotation was
    noted, I suspect.


    Nonnymus
    Name and email address faked
    to reduce spamming and kooks
     
  7. dAz

    dAz Guest

    done by calculating the time difference between the drop and unlocking
    of the escapement, so its the sound of the roller hitting the pallet
    fork and unlocking the escapement, the impulse as the escape wheel
    slides across the pallet and the drop as the now freed escape wheel
    tooth hits the locking face of the other pallet, those are the two
    loudest sounds the unlocking and the drop.

    have a look here for ideas
    http://www.bmumford.com/microset.html
    http://www.bmumford.com/mset/tech/watches/tickdsp.html

    I do use this machine and find very good for clock work, I have yet to
    buy the software but will do so soon, I have never bothered with a
    amplitude meter for watches because I can tell just by looking at the
    balance to whether it has good or bad amplitude, it would be nice to
    have one but could not justify the cost of a gradoscope to go with the
    vibrograph b200, the only real advantage I could see it could measure
    the amplitude while the watch is still closed up.
     
  8. "Spehro Pefhany"
    Ok thank you. :) I found some info mentioning what you just said, but
    no specific equation. I must admit that my math skills aren't up to
    figuring it out myself, so my quest continues to find the secret
    formula.

    So far I have only been experimenting with clocks and quartz watches.
    Clocks tend to be much louder therefore they are easier to "hear" than
    watches. I'm trying to come up with a good technique for hearing the
    watch, but as little ambient noise as possible. Any ideas on a good way
    to attach a microphone so as to hear thru mechanical conduction of the
    sound and not the sounds traveling thru the air.
     
  9. "dAz"
    Thanks for the reply dAz as always. After reading that, I'm thoroughly
    confused as to how the drop factors in. It seems that mainspring
    tension, train friction and other factors would determine the amount of
    time that it takes for the escape wheel to advance. I don't see how
    that would relate to balance wheel swing at all.

    I could see how the duration of the impulse sound could give a clue to
    the speed (and consequently the swing angle) of the balance wheel.
    That is my intent exactly. Now for a really stupid question. Given a
    300 degree swing, does that mean the balance swings 150 degrees each way
    using the stopped/neutral position as the center reference? IOW, would
    the maximum amount of swing (where the jewel continues around full
    circle after flipping the pallet and then hits the outside of the fork)
    be considered as ~720 degrees of swing or ~360 degrees?
     
  10. Jon Elson

    Jon Elson Guest

    Get a crystal phono pickup, and attach the needle mount to the watch.
    This is the "poor man's" vibration mike, known in the trade as a
    vibration accelerometer. You might have more luck buying a complete
    cheap phonograph at a flea market than just buying the pickup.
    You can also try to get an Endevco accelerometer on eBay, but these
    will be expensive unless you get lucky.

    Quartz watches? With mechanical movements, or all electronic? It
    may be possible to pick up the vibration of the crystal in a quartz
    watch, but that sounds extremely difficult.

    Jon
     
  11. Ok, thanks for the tip. I'll look into that.
    I'm primarily interested in mechanical watches for this particular
    puzzle.

    Some quartz watch analyzers seem to be listening to the 32kHz
    oscillator. The inductive pickup that I made from a Ford starter
    solenoid coil doesn't really hear that frequency, but it's real good at
    picking up the stepper impulses every second, you don't even have to
    remove the watch. Just bring it within a couple of inches of the coil
    and you're in business:) A PIC chip takes 24 bit readings (1uS
    precision) of the intervals and feeds them serially to a PC. Perfect
    precision for timing quartz watches, but kinda absurd (by several orders
    of magnitude) for 100 year old spring driven clocks.
     
  12. The Baron

    The Baron Guest

    What machines claim to do this?
     
  13. I don't think it's very challenging. You know from calculus & Hooke's
    law that the balance wheel angle follows a sinusoid wrt time, right?
    Do horologists refer to the peak angle or the peak-to-peak angle?
    Sprung lever? Enclosure with foam rubber lining?


    Best regards,
    Spehro Pefhany
     
  14. dAz

    dAz Guest

    well its worked on sound and duration I suppose, the unlock and drop are
    the two loudest sounds the escapement makes, but to human ears we only
    hear one sound as a tick

    you could work out the amplitude by the time taken for the balance to
    swing from the drop to the unlock, or the speed it takes from unlock to
    drop which probably why the beat count and lift angles are needed for
    that calculation.

    well Ideally a watch balance swings at around 270degs, that is from the
    neutral or centre point with the roller pin stopped dead in line with
    the pallet fork to swing around 3/4 either way or 270degs, thats one beat.

    again ideally this is with a movement in top condition, the mainspring
    is delivering smooth even power for most of the running of the watch,
    the hairspring is correctly formed to preserve the isochronism to
    compensate for variations in amplitude.

    under 270degs you start having problems with timekeeping, any shocks the
    watch recieves it takes longer for it to recover the swing,

    over 270degs you run into the danger of overbanking where the roller pin
    hits the outside of the pallet fork and gets an acceleration to the
    swing which again affects timekeeping.
     
  15. dAz

    dAz Guest

    yeah I wouldn't worry about reading the quartz frequency, on older
    first generation quartz with trim caps you could have adjusted rate via
    the frequency.

    modern movements with a couple of exceptions don't adjust the quartz to
    affect the rate, its done by the integrated circuit controlling the
    motor steps, in the cheap movements there is a pad of tracks where one
    or more are cut to set the rate, others use a once only programable chip
    or the better ones use an eeprom that can be reset by the use of the
    witschi timer.

    commercial watch timers either go by the magnetic pulse from the
    stepping motor or for LCD the pulse from the display.

    with the eeprom fitted movements you cannot really rely on just the
    motor pulses either, because the circuit constantly corrects the output
    from minute to minute, you would need to take a reading for several
    minutes then do an average in seconds per day to get the correct rate
    before clearing and rewriting the eeprom, this is what the $3000 witschi
    machine does, it also measures coil resistance, power consumption etc.

    a quartz timer is a waste of space, most quartz you cannot adjust
    because they are fixed, if a quartz watch doesn't keep time you either
    service the movement or fit a new one.
     
  16. That last page makes it pretty clear what is going on.

    A watch escapement passes through an angle equal to the lift angle
    between the time from the unlock sound to the drop sound (Td). Since the
    escapement is moving at the beat frequency (Fb), it is easy to calculate
    the total amplitude of the escapement given these figures.

    Amplitude = 2 * Lift Angle / sin( 360 * Fb * Td )

    Someone else suggested using a phonograph pickup to aquire the
    escapement sound. From the description of the commercial device, you
    might be able to use the sound card in a PC plus some cheap PC scope
    software to sample the waveform. By making a time measurement, you
    should be able to perform the same calculation that the commercial unit
    does.
     
  17. Thanks Paul! That indeed seems to give me numbers very close to his
    example. Not exactly the same for some odd reason, but within a few
    degrees.

    Perhaps I'm too dense to understand this, but I still don't see how the
    amount of time it takes the escape wheel to advance directly relates to
    balance amplitude. Once the pallet unlocks the escape wheel tooth from
    the entrance pallet jewel, the escape wheel will advance freely and with
    no influence from the balance wheel until it slams into the exit pallet
    jewel. AFAICT, it advances purely based upon train friction, the mass
    of the escape wheel and the amount of mainspring force trying to push it
    forward.
    I already have the interval measuring equipment (PIC based), I just need
    to be able to amplify and distinguish these tiny sounds. The
    calculations will be easy.
     
  18. Er umm no actually. I haven't much of a clue about calculus. :-( I
    know what it can do, just not how to use it to get the job done. One of
    the perils of not going to college I suppose. After a couple of decades
    of relative non use, even my trig capabilities have suffered. Paul's
    formula seems to be correct and certainly should be easy enough to
    implement even inside of a PIC. I'll be the envy of all at the trade
    shows with my $20 pocket beat analyzer. ;-)
    As you've probably already seen, dAz gave a nice description. Seems to
    be peak angle. I've been messing with clocks for years, but watches are
    a new hobby. Funny how similar and yet different they are.
    By "sprung lever" do you mean something like an alligator clip glued to
    the microphone?
     
  19. Agree wtih Jon re. the crystal pickup. AFAIK, there was no "magic" in the
    old chrono-analyzers. It seems to me they had to be only very sensitive
    audio devices. Could they have used elaborate audio filtering to emphasize
    certain elements of the sound? Possible, I suppose, but highly doubtful.
    Perhaps the audio waveform could be viewed on an o'scope in such a way to
    discern specific parts of the sound waveform. I haven't tried this. I do
    know you can't read the 32 kHz signal on an ordinary service monitor.

    Bob Swinney
     
Ask a Question
Want to reply to this thread or ask your own question?
You'll need to choose a username for the site, which only take a couple of moments (here). After that, you can post your question and our members will help you out.
Electronics Point Logo
Continue to site
Quote of the day

-