Le 19/12/2011 06:47, Perry Sandeen a écrit :

Dunno, but  some  10-50MHz TCXO/VCTCXO are now available in 2mm
packages, so why not.  There might  be battery longevity issues with
driving the higher frequency.  I guess it comes down to whether the
maker can sell enough to make a profit.
FWIW, My Citizen Chronomaster is has gained just 1,8 seconds in the last
12 months , well within the spec. of +/-5s.

I think the Grand Seikos are specified at the same +/- 10 seconds a
year accuracy as that Bulova. They use a slightly different approach
though - it's a standard 32768 Hz xtal, but its thermally compensated.
I don't know of any other watches that use a 262144 Hz xtal on its
own, but there were some designs that used both a 32768 and 262244 Hz
xtals and used the tracking between them for temperature compensation
(I think this was used in some Seiko and ETA watches).  The Bulova
certainly has a great price for a watch of that spec.

I don't know of any watches that used an oscillator as high as 10 MHz

• the highest clock I ever heard of in a watch was in a very limited
  edition Citizen that ran at 4 MHz, and which was specced at +/- 3
  seconds a year without thermal compensation. Omega also made a
  high-frequency watch that I think ran at 2.4 MHz and had a +/- 5
  seconds / year accuracy spec. Both of these used AT-cut xtals and
  suffered from rather poor battery life (about 1 year).

Regards,

Pete

On Mon, Dec 19, 2011 at 1:47 PM, Perry Sandeen sandeenpa@yahoo.com wrote:

With the CMOS logic used in watches, the big power hog
is due to charging and discharging the gate capacitance
of the various logic gates.  The faster you charge and
discharge the gate's, the more power you loose due to
I2R losses, and E-M radiation.

Thankfully, the high capacity lithium cells available today
provide lots more uA-hours than the older silver-oxide cells
of yor, so it is possible for the energy budget on a
premium electronic watch to be higher than was previously
acceptable.  I would think that most watch manufacturers would
take that extra power budget, and use it to extend the time
between cell changes, and to spin more fancy dial motors.

It is not clear to me that a 32KHz xtal is any less stable
than a 262KHz xtal, though.  I would think there would be a lot
more to be gained by using a microprocessor/thermistor to
measure the temperature within the watch, and provide an
adjustment to compensate for the xtal's natural temperature
sensitivity.

-Chuck Harris

Perry Sandeen wrote:

On 12/19/2011 5:34 AM, Chuck Harris wrote:

Chuck, I have recently made a couple of Real Time Clocks for my homebrew
radios using the Maxim DS3232 IC which has a built in TCXO at 32+ kHz
doing what you describe, the temperature is checked at intervals and the
corrections applied.  The performance is excellent, once set, getting to
what I term "Harrison Level", i.e. less than a second a week error.
The downside is that the standby battery demand is pretty high and my
first builds using a Lithium button cell ran for only around a month
max, so I had to go over to NiMH rechargeables.  I suspect using this
technology in a watch one would have the same problem.

The best crystals for room temperature use are around 4 MHz with
temperature inflections around 20C, and this is what was used in an
early Braun alarm clock I had which also had this kind of performance.
Long gone, alas.

Dan

How about a turnip pocket watch with one of the new Cesium standards in it?
Harrison would approve...
Don

mike cook

--
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are as significant as experiment, for thence comes quiet to the mind."
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Dr. Don Latham AJ7LL
Six Mile Systems LLP
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Looking at the datasheet for the DS3232, it doesn't appear
that they mean for it to run off of a small coin cell in a
watch.  Its battery operating capability is purely to keep
it running when the main power is turned off.

I would suspect that the DS3232's power consumption is due
to its being able to drive sizable loads on its various pins.

There is nothing inherent in temperature correcting a clock
that should take significantly more power than would be used
in a normal watch chip.  Measuring the temperature would be
the most power hungry operation, I would suspect... but
fortunately that doesn't have to be done all that often,
perhaps once per minute.

After the temperature is measured, a lookup table can be used
to find a second by second correction value to be added to
the seconds counter.

-Chuck Harris

Dan Rae wrote:

Why don't they build a watch that measures the temperature and every time
you accurately set it, it adds to a small database of time change v
temperature and then adjusts itself internally.

Over time it would become quite accurate I would think.

Jim

On 20 December 2011 11:12, Chuck Harris cfharris@erols.com wrote:

On Mon, 19 Dec 2011 19:12:43 -0500
Chuck Harris cfharris@erols.com wrote:

Juup, it definitly should not draw much power.
I own a Tissot T-Touch (first gen) that goes wrong
less than 5s/y, ie it's definitly temperature compensated.
Battery lifetime is several years (i actually dont know
because i had to bring it back for repairs in shorter intervals
than the battery holds)

		Attila Kinali

--
Why does it take years to find the answers to
the questions one should have asked long ago?