A
movement in watchmaking is the mechanism that measures the passage
of time and displays the current time (and possibly other information
including date, month and day). Movements may be entirely mechanical,
entirely electronic (potentially with no moving parts), or a blend
of the two. Most watches intended mainly for timekeeping today
have electronic movements, with mechanical hands on the face of
the watch indicating the time.
Mechanical Movements
Purely mechanical watches are still popular, although they are
most commonly seen among medium-to-high priced luxury watches
such as Fortis, Omega,
Rolex
and TAG
Heuer and very expensive high-end luxury watches
like Patek
Phillipe, Vacheron
Constantin, Ulysse Nardin and Audemars
Piguet. Their superb craftsmanship accounts for
much of the attraction of purely mechanical watches. Compared
to electronic movements, mechanical watches keep very poor time,
often with errors of seconds per day. They are frequently sensitive
to position and temperature, they are costly to produce, they
require regular maintenance and adjustment, and they are more
prone to failure.
Generally speaking, inexpensive and moderately priced timepieces
with electronic movements now provide most users with timekeeping
more accurate than the most expensive Rolex
or Patek
Phillipe. While the most expensive Rolex
contains the same movement as its less expensive C.O.S.C rated
brethren and all modern models can keep time to within one second
a day once the watches' daily rate is known. This is because the
number of rubies on the inside has a greater effect on precision
than the number of gems encrusting the precious metal case. Leaving
the watch in a certain position overnight will allow the watch
to gain or lose against the daily rate. However, in recent times
while there has been less emphasis on ones watch for time precision
as many people now carry multiple devices that will tell them
the time accurately such as mobile phones, PDAs and laptops, these
finely crafted mechanical watches have remained popular as precision
time pieces and in many cases more so because of their aesthetic
value as jewelry.
Tuning-Fork
Movements
Tuning
fork watches (introduced by Bulova
in 1960) use a tuning fork at a precise frequency (most often
360 hertz) to drive a mechanical watch. Since the fork is used
in place of a typical balance wheel, these watches naturally hum
instead of tick.
The inventor, Max Hetzel, was born in Basel, Switzerland, and
joined the Bulova
Watch Company of Bienne, Switzerland, in 1948. Hetzel was the
first to use an electronic device, a transistor, in a wristwatch.
Thus, he developed the first watch that could be qualified as
electronic. However, fork movements are actually more "electrical",
like an old electrical wall clock, than electronic. The sweep
second hand moves fluidly like that of an old electrical wall
clock.
Such watches were also sold by Swiss watch companies under license
of Bulova. In 1974, after leaving Bulova,
Hetzel developed a different tuning fork drive for Omega
Watches. The watch featured a cal. 1220 micromotor,
and a tuning fork frequency of 720 hertz. This development was
obsolete compared to the newer electronic quartz watch which had
become cheaper to produce and even more accurate.
Tuning fork movements are electromechanical. The task of converting
electronically pulsed fork vibration into rotary movement is done
via two tiny jeweled fingers, called pawls, one of which is connected
to one of the tuning fork's tines. As the fork vibrates, the pawls
precisely ratchet a tiny index wheel. This index wheel has over
300 barely visible teeth and spins more than 38 million times
per year. The tiny electric coils that drive the tuning fork have
8000 turns of insulated copper wire with a diameter of 0.015 mm
and a length of 90 meters. This amazing feat of engineering was
prototyped in the 1950s.
Electronic
Watch Movements
Electronic
movements have few or no moving parts. Essentially, all modern
electronic movements use the piezoelectric effect in a tiny quartz
crystal to provide a stable time base for a mostly electronic
movement: the crystal forms a quartz oscillator which resonates
at a specific and highly stable frequency, and which can be used
to accurately pace a timekeeping mechanism. For this reason, electronic
watches are often called quartz
watches. Most quartz movements are primarily electronic
but are geared to drive mechanical hands on the face of the watch
in order to provide a traditional analog display of the time,
which is still preferred by most consumers.
The first prototypes of electronic quartz
watches were made by the CEH research laboratory
in Switzerland in 1962. The first quartz watch to enter production
was the Seiko 35 SQ Astron, which appeared in 1969. Modern quartz
movements are produced in very large quantities, and even the
cheapest wristwatches typically have quartz movements.
The best quartz movements are significantly more accurate than
the worst, but the difference is much smaller than that found
between mechanical movements and quartz movements. Quartz movements,
even in their most inexpensive forms, are an order of magnitude
more accurate than purely mechanical movements. Where mechanical
movements can typically be off by several seconds a day, an inexpensive
quartz movement in a child's wristwatch may still be accurate
to within 500 milliseconds per day-ten times better than a mechanical
movement.
Quartz
watch mechanisms usually have a resonant frequency of
32768 Hz, chosen for ease of use (being 215). Using a simple 15
stage divide-by-two circuit, this is turned into a one pulse per
second signal responsible for the watch's keeping of time.
Radio-Controlled
Watch Movements
Some
electronic quartz watches
are able to synchronize themselves with an external time source.
These sources include radio time signals directly driven by atomic
clocks, time signals from GPS navigation satellites, the German
DCF77 signal in Europe, and others. These watches are free-running
most of the time, but periodically align themselves with the chosen
external time source automatically, typically once a day.
Because
these watches are regulated by an external time source
of extraordinarily high accuracy, they are never off by more than
a small fraction of a second a day (depending on the quality of
their quartz movements), as long as they can receive the external
time signals that they expect. Additionally, their long-term accuracy
is comparable to that of the external time signals they receive,
which in most cases (such as GPS signals and special radio transmissions
of time based on atomic clocks) is better than one second in three
million years. For all practical purposes, then, radio-controlled
wristwatches keep near perfect time.
Movements
of this type synchronize not only the time of day but also the
date, the leap-year status of the current year, and the current
state of daylight saving time (on or off). They obtain all of
this information from the external signals that they receive.
Because of this continual automatic updating, they never require
manual setting or resetting.
A
disadvantage of radio-controlled movements is that they cannot
synchronize if radio reception conditions are poor. Even in this
case, however, they will simply run autonomously with the same
accuracy as a normal quartz
watch until they are next able to synchronize.
