A quartz clock is a clock that uses an electronic oscillator that is regulated by a quartz crystal to keep time. This crystal oscillator creates a signal with very precise frequency, so that quartz clocks are at least an order of magnitude more accurate than mechanical clocks.
Generally, some form of digital logic counts the cycles of this signal and provides a numeric time display, usually in units of hours, minutes, and seconds. The first quartz clock was built in 1927 by Warren Marrison and J.W. Horton at Bell Telephone Laboratories. Since the 1980s when the advent of solid state digital electronics allowed them to be made compact and inexpensive, quartz timekeepers have become the world’s most widely used timekeeping technology, used in most clocks and watches, as well as computers and other appliances that keep time.
Chemically, quartz is a compound called silicon dioxide. Many materials can be formed into plates that will resonate. However, quartz is also a piezoelectric material: that is, when a quartz crystal is subject to mechanical stress, such as bending, it accumulates electrical charge across some planes.
In modern quartz clocks, the quartz crystal resonator or oscillator is in the shape of a small tuning fork, laser-trimmed or precision lapped to vibrate at 32,768 Hz. This frequency is equal to 215 cycles per second. A power of 2 is chosen so a simple chain of digital divide-by-2 stages can derive the 1 Hz signal needed to drive the watch’s second hand. In most clocks, the resonator is in a small can or flat package, about 4 mm long. The reason the 32,768 Hz resonator has become so common is due to a compromise between the large physical size of low frequency crystals for watches and the large current drain of high frequency crystals, which reduces the life of the watch battery. During the 1970s, the introduction of metal–oxide–semiconductor (MOS) integrated circuits allowed a 12-month battery life from a single coin cell when driving either a mechanical Lavet type stepping motor or a liquid crystal display (in an LCD digital watch). Light-emitting diode (LED) displays for watches have become rare due to their comparatively high battery consumption.
The relative stability of the quartz resonator and its driving circuit is much better than its absolute accuracy. Standard-quality resonators of this type are warranted to have a long-term accuracy of about 6 parts per million (0.0006%) at 31 °C (87.8 °F): that is, a typical quartz clock or wristwatch will gain or lose 15 seconds per 30 days (within a normal temperature range of 5 °C/41 °F to 35 °C/95 °F) or less than a half second clock drift per day when worn near the body.
The first quartz crystal oscillator was built by Walter G. Cady in 1921. In 1923, D. W. Dye at the National Physical Laboratory in the UK and Warren Marrison at Bell Telephone Laboratories produced sequences of precision time signals with quartz oscillators. In 1927, the first quartz clock was built by Warren Marrison and J.W. Horton at Bell Telephone Laboratories.
The world’s first prototype analog quartz wristwatches were revealed in 1967: the Beta 1 revealed by the Centre Electronique Horloger (CEH) in Neuchâtel Switzerland, and the prototype of the Astron revealed by Seiko in Japan. (Seiko had been working on quartz clocks since 1958).
In December 1969, Seiko produced the world’s first commercial quartz wristwatch, the Astron. This watch was released just prior to the introduction of the Swiss Beta21, which was developed by 16 Swiss Watch manufactures and used by Rolex, Patek and famously Omega in their electroquartz models.
Quartz timepieces have dominated the wristwatch and clock market since the 1980s. Because of the high Q factor and low temperature coefficient of the quartz crystal, they are more accurate than the best mechanical timepieces, and the elimination of all moving parts makes them more rugged and eliminates the need for periodic maintenance.