The properties of quartz crystals have been known for over a century.
Quartz is a piezoelectric material, meaning that it generates an electrical charge when mechanical pressure is applied. These crystals also vibrate when a voltage from an outside source, such as a battery, is applied. Piezoelectricity was discovered by Pierre Curie and his brother Jacques in 1880. In the early 1920s W.G. Cady recognized that, due to their elastic qualities, mechanical strength and durability, quartz crystals could be used to fabricate very stable resonators. Cady also concluded that the crystal could be cut in specific ways that would create resonators of almost any frequency that were practically independent of temperature variations. Quartz crystals were first used as a time
standard by Warren Marrison, who
invented the first quartz clock in 1927. Juergen Staudte invented a method for mass-producing quartz crystals for watches in the early 1970s.
The frequency of the quartz oscillator is determined by the cut and shape of the quartz crystal.
The quartz crystals inside watches today come in various shapes and frequencies. The most common crystals are miniature encapsulated tuning forks which vibrate 32,768 times per second. Other types of crystals vibrate at more than 50 million times per second.
The oscillations of the balance wheel provide the time standard in
In contrast, in the history of mechanical watches, the balance
wheel oscillated first at 2.5, then at 3, and finally at 5 cycles per second.
For more information about quartz oscillators, visit the IEEE's Frequency Control website at www.ieee.org/uffc/fc
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