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LOL - this is why our spouses/significant others/etc. think we're half-crazy a 
lot of the time. Or maybe they're on to something...  ;-)

Thanks for a good read, Gary.  :-)

--
GregR



--- On Wed, 9/16/09, Gary LaPook  wrote:

> From: Gary LaPook 
> Subject: [NavList 9766] Re: How Many Chronometers?
> To: navlist@fer3.com
> Date: Wednesday, September 16, 2009, 10:37 AM
> 
> 
> 
>   
>   
> 
>  
> As usual, George is right again (mostly.)� I will keep
> the watches is
> the freezer for a while longer but even the� short
> time period so far
> has shown a considerable change in the rates of the
> watches. The
> temperature in the freezer has been in the range of 1�
> F to - 10�F, say
> an average of about -5� about 80�F (45� C)
> lower than before. In the
> 10.3 hours that they have been in the freezer so far they
> have lost
> 1.5, 1.5 and 1.0 seconds corresponding to daily rates of
> -3.5, -3.5 and
> -2.3 seconds per day. Based on their performance in the
> past they
> should have each gained some small amount but that is lost
> in the
> imprecision of my reading of the watches compared to the
> WWV time
> signals, about one half second resolution. George predicted
> a change of
> rate of 7 or 8 seconds per day with this change in average
> temperature
> but the observed change in the short period so far is only
> about half
> of that but this might be masked by the imprecision of the
> readings
> also.
> 
> 
> 
> Apache Runner provided a formula for the change in
> frequency of the
> watch crystal as:
> 
> 
> 
> "Quartz crystals have the great advantage that they
> have very little
> temperature dependence.�� Typically, they're
> fabricated to have a
> minimum sensitivity to temperature around 25 degrees C.
> 
> 
> 
> As I
> recall, the dependence is roughly a quadratic, and goes
> like the square
> of the difference in temperatures - departures from 25
> degrees C.�� The
> coefficient is something like 0.04 ppm/(degrees C)**2
> 
> 
> 
> So, at freezing, one might expect 25 ppm shift, which is 2
> seconds
> per day - pretty significant, if I consider that my typical
> systematic
> drift is 0.1 seconds per day at standard temp's."
> 
> 
> 
> Using this formula would also predict a change of rate of 7
> seconds per
> day which hasn't happened so for but we will follow it
> for a while
> longer. Assuming that this formula is approximately
> correct, a change
> of average temperature of 5�C would predict a change
> of rate of .09
> seconds per day and a change of 10�C would cause a
> change of .35
> seconds per day. 
> 
> 
> 
> So I disagree with George to the extent that if the watches
> are kept in
> an insulated box, to limit the effect of diurnal changes in
> cabin
> temperatures, then the change in rate will only happen
> based on long
> term changes in ambient temperature, say on a cruise from
> the Caribbean
> to England. But, if the cabin is kept in a range of
> temperatures which
> are habitable for humans then the change of rates can be
> kept to a
> small number. 
> 
> 
> 
> And my advice for anyone wanting to use these watches for
> celestial
> navigation on an expedition across Antarctica is to duct
> tape them to
> your stomach under all of your clothes which will turn you
> into a
> temperature stabilizing "oven" for the crystals.
> Off course, prior to
> your expedition, you must determine their rates by wearing
> them taped
> to your stomach for some reasonable period of time.
> 
> 
> 
> gl
> 
> 
> 
> George Huxtable wrote:
> 
>   Gary wrote-
> 
> "So I have decided to extend my experiment. I have
> just placed all thee 
> watches in my freezer which is at -7� right now (along
> with the recording 
> thermometer) and will see what the rates are after three
> weeks and I will 
> report back then."
> 
> Let me predict that Gary will then see all three watches
> losing about 7 or 8 
> seconds a day (if he's talking about temperatures
> measured in Fahrenheit 
> degrees).
> 
> Quartz crystal frequencies do change with temperature, but
> not necessarily 
> in a linear way. By choosing the way that the crystal is
> cut, it's possible 
> to make its resonant frequency change parabolically with
> temperature, such 
> that it's a maximum at a convenient ambient temperature
> (such as 25� C) and 
> falls away either side, at temperatures that are higher or
> lower. This means 
> that it's most constant over the range of ambient
> temperatures that a watch 
> has to live in. (I understand that in some circumstances
> crystal oscillators 
> can be made to give a point-of-inflection rather that a
> maximum frequency at 
> that temperature, which can extend the useful temperature
> range somewhat 
> further.)
> 
> But, as with any such parabolic variaition, once you get
> away from the 
> optimum temperature, the dependence on temperature becomes
> more severe.
> 
> In the freezer, Gary will be operating his watches at about
> 47�C below their 
> optimum temperature of 25�C. Similarly, I would expect
> that if he operated 
> them at 47�C, above it, at 72�C, if they will
> stand that (he may be 
> understandably reluctant to try), then I would expect them
> to run similarly 
> slow, 7 or 8 seconds a day.
> 
> Wearing a watch on the wrist well help to keep its
> temperature up in the 
> daytime, but won't help much if it's taken off at
> night, in many 
> environments (such as small craft) that don't expect
> central heating. Nor 
> will "wrapping the watch in blankets"; an
> inanimate object will derive 
> little benefit from such attentions, much less than  Gary
> or I would. They 
> will only delay changes in ambient temperature reaching the
> watch; but they 
> will get to it in the end.
> 
> Gary refers to the use of a "crystal oven", to
> compensate for changes in 
> ambient temperature. Indeed, that's a viable
> technology, that I was using 
> for precise time measurement, 40 years ago. The crystal is
> put into a little 
> insulated housing containing a heating element and a
> temperature sensor, 
> with feedback to keep the crystal's temperature
> constant. It's done that 
> way, because it's so much easier to heat things above
> ambient temperature 
> than to cool them below it. An operating  temperature is
> chosen that's 
> higher than the environment is ever expected to reach
> (40�C, say) and a 
> crystal is chosen which has its optimum temperature to
> correspond. Such an 
> oscillator has its own "warm-up" period, after
> switch-on, until the oven 
> stabilises. This technique is seldom used for anything
> portable, unless 
> unavoidable, because of the power consumption by the oven.
> 
> George.
> 
> contact George Huxtable, at  george@hux.me.uk
> or at +44 1865 820222 (from UK, 01865 820222)
> or at 1 Sandy Lane, Southmoor, Abingdon, Oxon OX13 5HX, UK.
> 
> 
> =====================
> 
> ----- Original Message ----- 
> From: "Gary LaPook" 
> To: 
> Sent: Wednesday, September 16, 2009 1:34 AM
> Subject: [NavList 9757] Re: How Many Chronometers?
> 
> 
> I remember when I first got involved with radios back in
> the '60s that I 
> coveted a high end radio that had an "oven" to
> keep the oscillator crystal 
> at a constant temperature to keep the radio frequency from
> drifting as the 
> crystal changed temperature. I now think, however, that
> that was mainly "a 
> self inflicted wound" due to the tubes (valves) in the
> radios having 
> "heaters" to "boil off" electrons from
> the cathodes in order to make the 
> tubes function which caused the radios to change
> temperature a lot and to 
> run quite hot. The young guys won't remember waiting
> for a radio to "warm 
> up" before it would start working but us old timers
> will remember the orange 
> glow coming out of the back of the radio from the glow of
> the "heaters" in 
> each tube. I clearly remember warming my hands on cold
> nights over the hot 
> radio.
> 
> I now wonder if the much less extreme swings of temperature
> that would be 
> expected in a wrist watch, or by a watch kept in an
> insulated box below 
> decks, would make a large change in the watch crystals'
> resonant frequency 
> affecting their rates in any significant way.
> 
> So I have decided to extend my experiment. I have just
> placed all thee 
> watches in my freezer which is at -7� right now (along
> with the recording 
> thermometer) and will see what the rates are after three
> weeks and I will 
> report back then.
> 
> gl
> 
> --- On Tue, 9/15/09, Werner Luehmann 
> wrote:
> 
> From: Werner Luehmann 
> Subject: [NavList 9737] Re: How Many Chronometers?
> To: navlist@fer3.com
> Date: Tuesday, September 15, 2009, 10:21 AM
> 
> 
> Sorry Gary, wrong conclusion. The problem with quartz
> watches (or any quartz
> driven oscillator) is their temperature dependance. Only
> under a constant
> temperature you would get constant "rates". For
> example, in high class
> radios the quartz is kept at a constant temperature higher
> than the ambient
> temperature in order to ensure frequency stabilty. In wrist
> watches
> compensating electronic devices can be used. But this is
> expensive and not
> found in 17 Dollars pieces, if at all.
> So unfortunately this cheap solution doesn't work for
> us.
> B.T.W.: I have some nice digital (and not too cheap)
> stopwatches (made by 
> the
> German manufacturer "Hanhart") that elected to
> adjust their rates according
> to the year's season ;-)
> 
> Werner
> 
>  Am Dienstag, 15. September 2009 11:22:33 schrieb Gary
> LaPook:
>   
>   
>     Based on our discussion, I became curious about
> the accuracy of digital
> watches and their suitability for use as chronometers so I
> went to my
> local TARGET store and purchased three identical watches
> for $17.00
> each, the cheapest that they had. I set them and let them
> run for a few
> days and, as I expected, they each had different rates.
> Based on this I
> labeled them "A", "B", and
> "C" in the order of their rates starting with
> the slowest. I then reset them to UTC at 0121 Z on May 28,
> 2009. I
> checked them against UTC from WWV eleven days later on June
> 8th and
> found that they were all running fast by 2, 4 and 7 seconds
> respectively
> and I worked out their daily rates as .1818, .3636, and
> .6363 seconds
> per day, respectively.
> 
> On July 11th, 44 days after starting the test, the watches
> were fast by
> 9, 17 and 28 seconds. Using the rates determined in the
> first 11 days
> the predicted errors would have been 8, 16 and 28 amounting
> to errors in
> prediction of 1, 1, and 0 seconds. If using these three
> watches for a
> chronometer we could average the three errors and end up
> with only a .66
> second error in the UTC determined by applying the daily
> rates to the
> three displayed times after 33 days from the last check
> against WWV
> which took place on June 8th.
> 
> I determined new rates now based on the longer 44 day
> period of .2045,
> .3864 and .6363 seconds per day, respectively.
> 
> On September 15th at 0800 Z (per WWV), 110 days after
> starting the
> test, I took a photo of the watches which I have attached.
> The photo
> shows the watches fast by 21, 41 and 69 seconds but by
> carefully
> comparing them individually with the ticks from WWV the
> estimated actual
> errors are 21.5, 41.8 and 69.0 seconds. Using the 44 day
> rates, the
> predicted errors are 22.5, 42.5, and 70 seconds giving the
> errors in the
> predictions of 1.0, 0.7 and 1.0 seconds which, if averaged,
> would have
> caused a 0.9 second error in the computed UTC after 66 days
> from the
> last check against WWV on July 11th.
> 
> If, instead, I used the 11 day rates then the predicted
> errors would
> have been 20.0, 40.0, and 70.0 seconds which would result
> in errors of
> prediction of -1.5, -1.8, and 1.0 which, if averaged, would
> cause and
> error in the computed UTC of -0.6 seconds after 99 days
> from the last
> check against WWV which would have been on June 8th in this
> example.
> 
> From this experiment it appears that fifty one dollars
> worth of cheap
> watches would give you a perfectly adequate chronometer.
> 
> gl
> 
> 
>     
>   
>   
> 
> 
> 
> 
> 
> 
> 
> 
>   
> 
> 
> 
> 
> 
> > 
>  
> 
> 
> 
> 

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