Climate change.....how does it affect you.......
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  1. #1
    Member lysanderxiii's Avatar
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    Climate change.....how does it affect you.......

    Well, your watch at any rate.

    Temperature compensating balances, low thermal expansion alloys, the problem of rate change due to temperature has been known for some time, and ways to counter it are actually pretty well understood.

    But, how bad does it get? I mean for the average watch we have today?

    Very few, if anybody, used an active temperature compensation system these days, too expensive and time consuming to adjust. No, the passive low thermal expansion alloy is the system of choice. This actually makes answering the question easier.

    There are about five or six alloys out there used for balance springs, all are some form of cobalt-nickel-chromium alloy. The better known alloys are the proprietary alloys of Nivarox, Anachron (Nivarox, part of SWATCH), Parachrom (Rolex) and SPRON (Seiko). How good are these alloys at compensating for temperature (or, more correctly, not allowing temperature to affect them.)

    We know that the limits for temperature variation set forth by ISO 3159, the specifications for chronometers is +/- 0.6 s/d/degree C for watches over 20 mm in diameter and +/- 0.7 s/d/degree C for watches equal to or under 20 mm. We also know that watches with the above mentioned alloys are capable of meeting these limits without resorting to other, fancier measures. So, we can conclude that the thermal expansion of the various alloys is sufficiently small that it alone can limit rate change due to temperature to 0.6 s/d/C.

    How many seconds per day will that be?

    Let us assume the watch was regulated in a cozy room with the thermostat set at 22 deg C, then worn 1) in the desert at 49 deg C, and 2) in the mountains at -10 deg C.

    1) The temperature change in this case is 27 deg C, for ease of calculation let’s round the rate change to 1/2 s/d/C, so the watch in this case will slow 13.5 s/d from its original regulated rate.

    2) The temperature change in this case is 32 deg C, so the watch will increase its rate by 16 s/d.

    A watch worn on the wrist will eventually reach some temperature that is near skin temperature, maybe 32-33 deg C, so an argument can be made that wearing the watch all the time will aid in the stability of the rate over removing it at night (and allowing it to cool down).

    What about quartz?

    I should just refer you to that 8,000 word novella by Bruce Reding over on the High Accuracy Quartz forum, but I will sum it up for the general, non-compensated quartz.

    First, the quality of the quartz crystal matters, the AT cut (it has to do with the orientation of the cut to the geometry of the crystal structure, see Figure 1) is the most used in watch due to the flat section around 25 deg C, seen in Figure 2.

    In Figure 3, however, you see that cutting errors (expressed in degrees off zero) result in more pronounced “waviness”.

    &

    Fig. 1) Orientation angle of a Z-plate quartz crystal


    Figure 2. Change in Frequency v. Temperature


    Figure 3. Change in Frequency v. Temperature v. Cut Angle

    In the case of a watch quartz operating at 32768 Hz, 50 PPM (parts per million) is about 4.32 sec/day. So a well cut quartz crystal (0 deg) should stay within +/- 1 sec/day in a temperature range from -20 to +80 deg C. A poorly cut one could vary as much as +/- 10 seconds over a similar temperature range.

    All quartz are not equal......
    Last edited by lysanderxiii; December 2nd, 2011 at 23:26.
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  2. #2
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    Re: Climate change.....how does it affect you.......

    LOL - I was just about to post that I change from bracelet to alligator strap...

    SOLID POST!
    Just getting started.

  3. #3
    Member dunl12496j's Avatar
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    I dont believe in climate change. But if it were real the changes would be very small.
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  5. #4
    Vintage & NAWCC Forum moderator Ben_hutcherson's Avatar
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    Re: Climate change.....how does it affect you.......

    If I may comment a little bit on mechanical watch temperature compensation...

    Historically, hairsprings were made of blue steel spring wire. The principle problem with this material in this application is not in its thermal expansion, but rather a variability in the elasticity of a spring made from it.

    Specifically, at lower temperatures, the elasticity increases, and at higher temperatures the elasticity decreases. This causes rate to increase at low temperatures and decrease at higher temperatures. This effect is significantly greater than any variation due to thermal expansion of the balance wheel and spring.

    The most practical solution to this was the cut rim laminated steel/brass balance wheel. Due to the differing coefficients of thermal expansion of the two materials, the arms tend to curl in and reduce the diameter of the balance at higher temperatures, and increase the diameter of the balance at lower temperatures.

    The bimetallic balance is fitted with some form of weight whose position along the balance arms can be adjusted to alter how much effect these changes in temperature have on the moment of inertia of the balance wheel. Originally, these were just simple weights which could be slid along the balance rim-later designs(by far and away the most common design) used brass or gold screws screwed into holes tapped along the rim.

    Typically, a split bimetallic balance was timed and adjusted at two temperatures-a "cold" temperature somewhere around freezing, and a "hot" temperature somewhere around body temperature. There's a problem with this, though, in that, due to the design of the balance, a watch that is timed correctly at the hot and cold temperatures will still be wrong at middle temperatures. George Daniels says that if the two temperatures chosen are 36 celcius and 4 celcius, the middle temperature error will amount to +2s/day.

    The principle strength of modern hairspring alloys lies not so much in their low thermal expansion, but rather in that the elasticity is essentially constant over the normal temperature operating range of a watch. One of the earliest such alloys was called "Elinvar", which is short for "Elastically Invariable." As said, though, these also are less than perfect, and are still sometimes combined with various other temperature compensating systems. In general, as shown above, an Elinvar or similar hairspring combined with an uncut monometallic balance wheel made of a low thermal expansion alloy will work well enough for most purposes. One of my personal best timekeepers is a Hamilton 992B, which has an "Elinvar Extra" hairspring and stainless steel balance.

    Aside from all of that-as alluded to above-there's a big advantage to not using cut bimetallic balances. Specifically, if these are not carefully handled during servicing, they can easily get out of shape, something that ruins the temperature compensation(as well as the positional adjustment).

    As a notable example, Hamilton's WWII era Model 21 marine chronometer(by many accounts one of the most precise mechanical timekeepers ever constructed) had an uncut bimetallic balance wheel that would "ovalize" under the correct temperature range to more fully correct for temperature variation. The Hamilton design used Invar arms combined with a stainless steel rim.

    George Daniels describes his own design of compensating balance which consists of an uncut stainless steel rim and arms. The arms have small bimetallic attachments which will cause slight changes to the moment of inertia.
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