[time-nuts] Need a Watch Recommendation

Thu Mar 15 15:24:53 EDT 2018

Hi

The most common way to pull the 32KHz signal off of a watch is via a tuned 
microphone. At least that’s the way we did it in production. A watch crystal 
*can* (but usually doesn’t) move > 100 PPM with temperature. When things 
are set up, assumptions are made about “your” temperature environment. If
the watch is off temperature vs the assumptions, it will not keep good time. 

Some numbers:

10 seconds a month is 3.8 ppm
120 seconds a month is 46 ppm 

The temperature curve is parabolic so *usually* temperature will result in a
slow watch. If the “target” set point is 10 seconds fast, you would need to 
be right at 50 ppm off to loose two minutes a month. 

If you take a look a the previous numbers on trim range on the trimmer. A 
trimmer that will do +/- 25 ppm is “adequate” for setting the watch in production.
It’s not good enough (by a factor of 2) to take care of a 2 minute / month timing 
error. 

Just for the record, I don’t think I have *ever* owned a quartz watch that was 
off by more than a 15 seconds per month. I’ve owned cheap ones and expensive
ones. They all have done pretty well. The fancy ones *have* done better ….

Bob

> On Mar 15, 2018, at 11:51 AM, Dana Whitlow <k8yumdoober at gmail.com> wrote:
> 
> Most of the quartz watches I've owned were off by about 1-2 minutes per
> month,
> which I consider inexcusable.
> 
> Agreed, the mechanical trimmer is rather problematical, but I'd sure like
> to see
> *something *that the sophisticated user can tweak at home. Measurement of
> the
> current rate error is probably not much of a problem; I once tried seeing
> the
> 32kHz signal in the watch by capacitive coupling to the face, and could
> detect
> the signal.  I just tried a token attempt on my current watch and failed,
> but it
> was a crude, unshielded attempt by merely laying a 'scope probe against the
> watch face.  I was being severely jammed by the local 1230 kHz AM station.
> Anyway, the idea is to observe the signal's phase drift while triggering
> the 'scope
> from a trusted 1PPS source.
> 
> So now all that's needed is an alternate way for trimming the watch's
> frequency
> without opening the case.  There must be a way...
> 
> Dana
> 
> 
> On Thu, Mar 15, 2018 at 8:13 AM, Bob kb8tq <kb8tq at n1k.org> wrote:
> 
>> Hi
>> 
>> 
>>> On Mar 15, 2018, at 1:33 AM, Dana Whitlow <k8yumdoober at gmail.com> wrote:
>>> 
>>> I concur with Bill.  And even if one keeps tabs on the current watch
>> error,
>>> as is the usual practice by celestial navigators, once that error reaches
>>> or exceeds more than a minute the process frankly gets more clumsy and
>>> error prone.  And if a watch drifts in time very rapidly, one loses faith
>>> in its
>>> ability to coast at a known rate between checks against WWV, which
>>> opportunities are not always available when one wants, due to
>>> propagation issues.
>>> 
>>> Whatever happened to the quartz watches with trimmer capacitors
>>> for setting the rate?
>> 
>> Trimmer caps to set watch crystals are problematic. They are a source of
>> error
>> as well as a set mechanism. You bump this or that and the trimmer moves.
>> They
>> also cost money to buy and install properly (no flux in-between the plates
>> …).
>> Once that is all done you need a way to set them in the factory. Back in
>> the day,
>> yes, we hat line workers who did that sort of thing. We also sold the
>> crystal in the
>> watch module (not the whole module) for $2 once upon a time.
>> 
>> How close do you want to set it? In our case, the set was supposed to be <
>> 0.5
>> ppm of the target. Ideally you needed a design that would do a small
>> fraction
>> of a ppm in a typical situation.
>> 
>> If the trimmer is a normal device, you get about 120 degrees of travel for
>> the
>> useful part of the tuning curve. A tune range of 30 ppm for the crystal
>> and another
>> 20 ppm for the other parts would not be unusual. Even taking the 0.5 ppm
>> number,
>> you are into 120 / 100 = 1.2 degrees sort of set on that little trimmer.
>> 
>> Bottom line: They went away because they weren’t good enough and they were
>> to expensive …. Setting a modern “shoot the chip” register based module is
>> way
>> more accurate and reliable. It’s silicon so the cost is whatever sand is
>> selling
>> for ….
>> 
>> Bob
>> 
>>> 
>>> And radio controlled?  No way!
>>> The process is to delicate and marginal to rely upon.  Give me a
>>> good stable free-running watch any day.
>>> 
>>> I don't like the solar watch concept mainly because one sometimes
>>> has to go for weeks without an opportunity to expose his watch to
>>> direct sunlight (or some indoor equivalent) for the requisite period
>>> of several hours.
>>> 
>>> Yesterday I was reading the manual for the Citizen ECO series,
>>> and that thing requires far too much effort and complication to keep
>>> it working and on time.  A good watch must simply work, with no
>>> maintenance beyond occasional battery replacements (and possible
>>> gland replacement at battery-change time), and accurately enough
>>> that the time need never be reset between battery replacements.
>>> 
>>> I use an old quartz diving watch I bought just under 10 years ago,
>>> (brand no longer distinguishable), which has never drifted more than
>>> about 30 sec (usually less) between battery replacements, and I never
>>> take it off between batteries except when compelled to do so at TSA
>>> checkpoints.  Aside from its LCD's failing I'd be happy to use if
>> forever,
>>> but it's getting awfully hard to read these days.
>>> 
>>> Dana
>>> 
>>> 
>>> 
>>> On Wed, Mar 14, 2018 at 10:54 PM, Bill Byrom <time at radio.sent.com>
>> wrote:
>>> 
>>>> On Wed, Mar 14, 2018, at 6:53 PM, Dr. David Kirkby wrote:
>>>>> What is the most demanding task one would use a wrist watch for?
>>>> 
>>>> It depends on your job or hobby.
>>>> 
>>>> During the Apollo 13 rocket burn before their emergency re-entry, Jack
>>>> Swigert used a wrist watch to time the retrorocket burn which was
>>>> manually controlled by Jim Lovell. Their normal capsule chronometer was
>>>> inoperative. This was mostly a differential (time interval) timing
>>>> measurement.
>>>> If you needed to determine your location (longitude) and all you had
>>>> was a wristwatch and a sextant (and software or a table with certain
>>>> information), the accuracy of the distance calculation would depend on
>>>> the absolute time accuracy of the watch. At the equator the longitude
>>>> error due to time error is (40,075.16 km/day) / (86,400 sec/day) =
>>>> 463.8 m/sec.
>>>> Amateur astronomers need to know time accurate to about a second or
>>>> better for accurate osculation observations.
>>>> Amateur Radio nets and phone, Skype for Business, or WebEx conference
>>>> calls usually start pretty close to the scheduled time. In some cases
>>>> people start wondering if the organizer is delayed after about 15 to
>>>> 30 seconds.--
>>>> Bill Byrom N5BB
>>>> 
>>>> 
>>>> 
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