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Wristwatch

Updated on September 2, 2010
Photo by Ahmed Al-Shukaili
Photo by Ahmed Al-Shukaili

A watch is a timekeeping instrument intended to be worn, usually on the wrist. Like clocks, watches indicate the time of day by hands, or pointers, that move at a regular pace around a graduated dial.

Hands to indicate the passage of seconds, minutes, and hours are all driven from a central shaft. The second hand, if there is one, travels around the face of the watch 60 times as fast as the minute hand, which travels 12 times as fast as the hour hand. These ratios are maintained by the gears that drive the various hands from the mam shaft. The main shaft is connected to a power source and is turned at the proper rate by small bursts of energy released to it by a precise vibrating or oscillating control mechanism. Jewel bearings, which are very durable, are used throughout the watch at points of friction and wear.

Types of Watches

The four types of watches in use are the mechanical watch, the automatic, or self-winding, watch, the electric watch, and the tuning-fork electronic watch (Accutron). Two of these types are powered by a mainspring, and the other two by a battery.

Kinds of Watch Mechanisms

Mechanical Watch

A mechanical watch is powered by a mainspring, which stores enough energy to last more than 24 hours. The mainspring must be wound by hand by means of the crown, a knurled knob outside the casing. Gears link the mainspring, drive shaft, and control mechanism together. The control mechanism consists of a balance wheel, hairspring, pallet, and escape wheel. The balance wheel oscillates, or moves back and forth, five times a second. As it swings in one direction, it causes the pallet to engage the escape wheel, which locks all the gears and prevents the mainspring's energy from being released to the drive shaft. As the balance wheel swings in the opposite direction, it disengages the pallet, freeing the escape wheel and allowing power to reach the drive shaft. Part of this power is transmitted to the balance wheel through the escape wheel and pallet, providing a. force in one of the directions in which the balance wheel oscillates. The hairspring, which is coiled inside the balance wheel, provides force in the opposite direction.

Automatic Watch

The self-winding watch is identical with the basic mechanical watch, except that its mainspring is wound automatically. (See diagram.) It contains a weight that is free to swing in response to the normal movements of the wearer of the watch. The weight is connected to the mainspring through gears that allow the movements of the weight in either direction to be used to wind the mainspring.

Electric Watch

The electric watch is powered by a tiny battery that lasts a year or more. The movement of the drive shaft is regulated by an oscillating balance wheel. Various arrangements are used to transmit power to the drive shaft. In the design shown in the diagram, an electromagnet powered by the battery reacts with a small permanent magnet on the shaft of the balance wheel, causing the balance wheel to turn against its hairspring. As the wheel turns in this direction, it breaks the electrical circuit that powers the electromagnet and can then turn back again, powered by the hairspring. The movement of the wheel in this direction causes the drive pin to push against a rod called the index finger, which drives a gear train linked to the drive shaft. As the balance wheel completes its swing, it causes the electric contacts to close, turning on the electromagnet, which then forces the wheel to turn in the opposite direction to begin a new cycle. A fixed pawl finger prevents movement of the gear train in this direction. In the electrical watch, as in a mechanical watch, the balance wheel oscillates five times a second.

Tuning-fork Electronic Watch (Accutron Watch)

This watch is also powered by a small battery. The regulating mechanism, which also transmits power to the gears driving the main shaft, is a tuning fork. The fork vibrates at a frequency of 360 cycles per second. As the fork travels in one direction, an index finger attached to it transmits power to the gear train.

The tuning fork is supplied with power through electromagnets connected to the battery. The electromagnets are placed opposite small permanent magnets set into the fork's tines, or prongs. The magnetic force between the electromagnets and the permanent magnets provides impulses that keep the fork vibrating with sufficient energy to drive the gear train and drive shaft. The electromagnets are turned on and off by an electronic circuit. A sensing coil that reacts to the movement of one of the permanent magnets on the fork sends pulses to the electronic circuit that indicate the motion of the fork. Tuning-fork electronic watches are accurate to within one minute per month.

History of the Watch

The development of the watch was due to important contributions made over four centuries by many individual craftsmen. Portable timekeeping instruments became possible with the invention of the mainspring by Peter Henlein of Nuremberg, Germany, in 1500. These early watches, some worn around the neck or on a belt, some small enough to fit in a pocket, were sometimes called Nuremberg eggs. Christiaan Huygens of the Netherlands is generally credited with the invention of the hairspring, in 1675. This invention reduced the size of watches. The escape mechanism was invented in 1765 by Thomas Mudge of England.

In the early 20th century, mass-production methods were applied to watchmaking, resulting in instruments of greater reliability and precision. Swiss watchmakers played an important role in this development. During the Boer War, British officers wore watches strapped to their wrists. After World War I, wristwatches became more popular and replaced the pocket watches.

The first practical self-winding watch was invented in about 1925 by John Harwood of England. The first practical electric watch was introduced by the Hamilton Watch Company in the United States in 1957. The tuning-fork electronic wristwatch, called Accutron, was developed by the Bulova Watch Company in the United States in 1960.

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