Quartz resonators- watches

Pendulums were more accurate, followed by quartz oscillators. In 1880, Pierre and Jacques Curie discovered that sending a current through a quartz crystal could result in a resonance situation with cyclic behavior, making a quartz oscillator that could be used to mark time. Because crystals grow in miniature, quartz crystal watches became the standard in the 1960s. But the periodic nature of resonant quartz excitations depends on the shape of each crystal as well as the ambient temperature and humidity. Every crystal behaves differently, and none can constitute a reputable standard for the accuracy needed by global positioning systems, for example. 

When it is struck or pressed, quartz generates an electric current. Materials having this property are known as piezoelectric materials. If an external voltage is applied across the crystal, the crystal undergoes vibrations that are in resonance with the alternating current frequency. This type of behavior is the basis for quartz being used as a timing device in watches or in crystals used to establish radio frequencies. 

The vibration induced by E allows the frequency of an electric resonant circuit (used, for example, in a quartz watch) to be stabilized. Quartz is also used in the manufacture of acoustic generators. The theory which accounts for this dynamic effect comprises the calculation of the elastic vibrations of the crystal (Section 4.4.3) induced by an alternating electric field E cos cot parallel to in the absence of external stresses. The importance of quartz is due to the fact that it is chemically inert and very stable, and, even if the elastic and piezoelectric constants vary with temperature, it is possible to cut crystal plates with orientations such that their natural frequencies are constant over a large temperature... 

The natural resonance frequency of a piezoelectric crystal may be used as a frequency standard. Quartz is the material of choice. Quartz crystal resonators provide highly stable crystal-controlled clocks and watches (constant to 1 part in 10 ) and control fixed frequencies... 

The device can be used to replace the tuned circuit in an oscillator by providing the resonant frequency or it can be coupled to the oscillator circuit, which is tuned approximately to the crystal frequency. In this type, the crystal prevents frequency drift. The device is widely used in quartz clocks and watches. 

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