Ain Shams University Faculty of Engineering Design and Production dep.
The Clocks
Presented By: Mina Farid Fouad Mina Samir Mosaad Mina Samir Aziz Mina Saleh Ayad Mina Nabil Nasr Mina Gad Seif
Stonehenge Celestial bodies, the sun, moon, planets, and stars have provided us a reference for measuring the passage of time throughout our existence. Ancient civilizations relied upon the apparent motion of these bodies through the sky to determine seasons, months, and years. Little is known about the details of timekeeping in prehistoric eras, however, records and artifacts that are discovered show that in every culture, people were preoccupied with measuring and recording the passage of time. Ice-age hunters in Europe over 20,000 years ago scratched lines and gouged holes in sticks and bones, possibly counting the days between phases of the moon. Five thousand years ago, Sumerians in the Tigris-Euphrates valley in today's Iraq had a calendar that divided the year into 30-day months, divided the day into 12 periods (each corresponding to 2 of our hours), and divided these periods into 30 parts (each like 4 of our minutes). There are no written records of the creating of Stonehenge, built over 4000 years ago in England, but its alignments show its purposes apparently included the determination of seasonal or celestial events, such as lunar eclipses, solstices and so on. The earliest Egyptian calendar was based on the moon's cycles, but later the Egyptians realized that the "Dog Star" in Canis Major, which is now called Sirius, rose next to the sun every 365 days, about when the annual inundation of the Nile began. Based on this knowledge, they devised a 365-day calendar that seems to have begun in 4236 B.C., the earliest recorded year in history. In Babylonia, again in Iraq, a year of 12 alternating 29-day and 30-day lunar months was observed before 2000 B.C., giving a 354-day year. In contrast, the Mayans of Central America relied on not only the sun and moon, but also the planet Venus, to establish 260-day and 365-day calendars. This culture flourished from around 2000 B.C. until about 1500 A.D. They left celestial-cycle records indicating their belief that the creation of the world occurred in 3113 B.C. Their calendars later became portions of the great Aztec calendar stones. Other civilizations, including the modern West, have adopted a 365-day solar calendar with a leap year occurring every fourth year.
Sun Clock, Water Clock, Obelisk Egyptian shadow clock with Obelisk: Not until somewhat recently (that is, in terms of human history) did people find a need for knowing the time of day. As best we know, 5000 to 6000 years ago great civilizations in the Middle East and North Africa initiated clock making as opposed to calendar making. With their attendant bureaucracies and formal religions, these cultures found a need to organize their time more efficiently.
Sun Clock: After the Sumerian culture was lost without passing on its knowledge, the Egyptians were the next to formally divide their day into parts something like our hours. Obelisks (slender, tapering, four-sided monuments) were built as early as 3500 B.C. Their moving shadows formed a kind of sundial, enabling citizens to partition the day into two parts by indicating noon. They also showed the year's longest and shortest days when the shadow at noon was the shortest or longest of the year. Later, markers added around the base of the monument would indicate further time subdivisions. Another Egyptian shadow clock or sundial, possibly the first portable timepiece, came into use around 1500 B.C. to measure the passage of "hours." This device divided a sunlit day into 10 parts plus two "twilight hours" in the morning and evening. When the long stem with 5 variably spaced marks was oriented east and west in the morning, an elevated crossbar on the east end cast a moving shadow over the marks. At noon, the device was turned in the opposite direction to measure the afternoon "hours". The merkhet, the oldest known astronomical tool, was an Egyptian development of around 600 B.C. Two merkhets were used to establish a north-south line by lining them up with the Pole Star. They could then be used to mark off nighttime hours by determining when certain other stars crossed the meridian. In the quest for more year-round accuracy, sundials evolved from flat horizontal or vertical plates to forms that were more elaborate. One version was the hemispherical dial, a bowl-shaped depression cut into a block of stone, carrying a central vertical gnomon (pointer) and scribed with sets of hour lines for different seasons. The hemicycle, said to have been invented about 300 B.C., removed the useless half of the hemisphere to give an
appearance of a half-bowl cut into the edge of a squared block. By 30 B.C., Vitruvius could describe 13 different sundial styles in use in Greece, Asia Minor, and Italy.
Elements of a Clock Having described a variety of ways devised over the past few millennia to mark the passage of time, it is instructive to define in broad terms what constitutes a clock. All clocks must have two basic components: A regular, constant or repetitive process or action to mark off equal increments of time. Early examples of such processes included movement of the sun across the sky, candles marked in increments, oil lamps with marked reservoirs, sand glasses ("hourglasses"), and in the Orient, small stone or metal mazes filled with incense that would burn at a certain pace. A means of keeping track of the increments of time and displaying the result. Our means of keeping track of time passage include the position of clock hands and a digital time display. The history of timekeeping is the story of the search for ever more consistent actions or processes to regulate the rate of a clock.
Water Clock Water clocks were among the earliest timekeepers that did not depend on the observation of celestial bodies. One of the oldest was found in the tomb of Amenhotep I, buried around 1500 B.C. Later named clepsydras ("water thief") by the Greeks, who began using them about 325 B.C., these were stone vessels with sloping sides that allowed water to drip at a nearly constant rate from a small hole near the bottom. Other clepsydras were cylindrical or bowl-shaped containers designed to slowly fill with water coming in at a constant rate. Markings on the inside surfaces measured the passage of "hours" as the water level reached them. These clocks were used to determine hours at night, but may have been used in daylight as well. Another version consisted of a metal bowl with a hole in
the bottom; when placed in a container of water the bowl would fill and sink in a certain time. These were still in use in North Africa this century. More elaborate and impressive mechanized water clocks were developed between 100 B.C. and 500 A.D. by Greek and Roman horologists and astronomers. The added complexity was aimed at making the flow more constant by regulating the pressure, and at providing fancier displays of the passage of time. Some water clocks rang bells and gongs; others opened doors and windows to show little figures of people, or moved pointers, dials, and astrological models of the universe. A Greek astronomer, Andronikos, supervised the construction of the Tower of the Winds in Athens in the 1st century B.C. This octagonal structure showed scholars and marketplace shoppers both sundials and mechanical hour indicators. It featured a 24-hour mechanized clepsydra and indicators for the eight winds from which the tower got its name, and it displayed the seasons of the year and astrological dates and periods. The Romans also developed mechanized clepsydras, though their complexity accomplished little improvement over simpler methods for determining the passage of time. In the Far East, mechanized astronomical/astrological clock making developed from 200 to 1300 A.D. third-century Chinese clepsydras drove various mechanisms that illustrated astronomical phenomena. One of the most elaborate clock towers was built by Su Sung and his associates in 1088 A.D. Su Sung's mechanism incorporated a water-driven escapement invented about 725 A.D. The Su Sung clock tower, over 30 feet tall, possessed a bronze powerdriven armillary sphere for observations, an automatically rotating celestial globe, and five front panels with doors that permitted the viewing of changing manikins which rang bells or gongs, and held tablets indicating the hour or other special times of the day. Since the rate of flow of water is very difficult to control accurately, a clock based on that flow could never achieve excellent accuracy. People were naturally led to other approaches.
Mechanical Pendulum Clock and Quartz Clock Pendulum used to keep time: In Europe during most of the Middle Ages (roughly 500 to 1500 A.D.), technological advancement was at a virtual standstill. Sundial styles evolved, but didn't move far from ancient Egyptian principles. During these times, simple sundials placed above doorways were used to identify midday and four "tides" of the sunlit day. By the 10th Century, several types of pocket sundials were used. One English model identified tides and even compensated for seasonal changes of the sun's altitude. Then, in the early-to-mid-14th century, large mechanical clocks began to appear in the towers of several large Italian cities. There is no evidence or record of the working models preceding these public clocks that were weight-driven and regulated by a verge-and-foliot escapement. Verge-and-foliot mechanisms reigned for more than 300 years with variations in the shape of the foliot. All had the same basic problem: the period of oscillation of this escapement depended heavily on the amount of driving force and the amount of friction in the drive. Like water flow, the rate was difficult to regulate. Another advance was the invention of spring-powered clocks between 1500 and 1510 by Peter Heinlein, a German locksmith from Nuremberg. Replacing the heavy drive weights permitted smaller (and portable) clocks and watches. Heinlein nicknamed his clocks "Nuremberg Eggs". Although they slowed down as the mainspring unwound, they were popular among wealthy individuals due to their size and the fact that they could be put on a shelf or table instead of hanging from the wall. They were the first portable timepieces. However, they only had an hour hand, minute hands did not appear until 1670, and there was no glass protection. Glass over the face of the watch did not come about until the 17th century. Still, Heinlein’s advances in design were precursors to truly accurate timekeeping. Accurate Mechanical Clock In 1656, Christian Huygens, a Dutch scientist, made the first pendulum clock, regulated by a mechanism with a "natural" period of oscillation. Although Galileo Galilee, sometimes credited with inventing the pendulum, studied its motion as early as 1582, Galileo's design for a clock was not built before his death. Huygens' pendulum clock had an error of less than 1
minute a day, the first time such accuracy had been achieved. His later refinements reduced his clock's errors to less than 10 seconds a day. Around 1675, Huygens developed the balance wheel and spring assembly, still found in some of today's wrist watches. This improvement allowed 17th century watches to keep time to 10 minutes a day. And in London in 1671 William Clement began building clocks with the new "anchor" or "recoil" escapement, a substantial improvement over the verge because it interferes less with the motion of the pendulum. In 1721, George Graham improved the pendulum clock's accuracy to 1 second a day by compensating for changes in the pendulum's length due to temperature variations. John Harrison, a carpenter and self-taught clockmaker, refined Graham's temperature compensation techniques and added new methods of reducing friction. By 1761, he had built a marine chronometer with a spring and balance wheel escapement that won the British government's 1714 prize (of over $2,000,000 in today's currency) offered for a means of determining longitude to within one-half degree after a voyage to the West Indies. It kept time on board a rolling ship to about one-fifth of a second a day, nearly as well as a pendulum clock could do on land, and 10 times better than required. Over the next century refinements led in 1889 to Siegmund Riefler's clock with a nearly free pendulum, which attained an accuracy of a hundredth of a second a day and became the standard in many astronomical observatories. A true free-pendulum principle was introduced by R. J. Rudd about 1898, stimulating development of several free-pendulum clocks. One of the most famous, the W. H. Shortt clock, was demonstrated in 1921. The Shortt clock almost immediately replaced Riefler's clock as a supreme timekeeper in many observatories. This clock consists of two pendulums, one a slave and the other a master. The slave pendulum gives the master pendulum the gentle pushes needed to maintain its motion, and also drives the clock's hands. This allows the master pendulum to remain free from mechanical tasks that would disturb its regularity. Quartz Clock The Short clock was replaced as the standard by quartz crystal clocks in the 1930s and 1940s, improving timekeeping performance far beyond that of pendulum and balance-wheel escapements. Quartz clock operation is based on the piezoelectric property of quartz crystals. If you apply an electric field to the crystal, it changes its shape, and if you squeeze it or bend it, it generates an electric field. When put in a suitable electronic circuit, this interaction between mechanical stress and electric field causes the crystal to vibrate and generate a constant
frequency electric signal that can be used to operate an electronic clock display. Quartz crystal clocks were better because they had no gears or escapements to disturb their regular frequency. Even so, they still relied on a mechanical vibration whose frequency depended critically on the crystal's size and shape. Thus, no two crystals can be precisely alike, with exactly the same frequency. Such quartz clocks continue to dominate the market in numbers because their performance is excellent and they are inexpensive. But the timekeeping performance of quartz clocks has been substantially surpassed by atomic clocks.
Atomic Clock and Time Standard Scientists had long realized that atoms (and molecules) have resonances; each chemical element and compound absorbs and emits electromagnetic radiation at its own characteristic frequencies. These resonances are inherently stable over time and space. An atom of hydrogen or cesium here today is exactly like one a million years ago or in another galaxy. Here was a potential "pendulum" with a reproducible rate that could form the basis for more accurate clocks. The development of radar and extremely high frequency radio communications in the 1930s and 1940s made possible the generation of the kind of electromagnetic waves (microwaves) needed to interact with the atoms. Research aimed at developing an atomic clock focused first on microwave resonances in the ammonia molecule. In 1949, NIST built the first atomic clock, which was based on ammonia. However, its performance wasn't much better than existing standards, and attention shifted almost immediately to more-promising, atomic-beam devices based on cesium.
In 1957, NIST completed its first cesium atomic beam device, and soon after a second NIST unit was built for comparison testing. By 1960, cesium standards had been refined enough to be incorporated into the official timekeeping system of NIST. In 1967, the cesium atom's natural frequency was formally recognized as the new international unit of time: the second was defined as exactly
9,192,631,770 oscillations or cycles of the cesium atom's resonant frequency replacing the old second that was defined in terms of the earth's motions. The second quickly became the physical quantity most accurately measured by scientists. The best primary cesium standards now keep time to about one-millionth of a second per year. Much of modern life has come to depend on precise time. The day is long past when we could get by with a timepiece accurate to the nearest quarter hour. Transportation, communication, manufacturing, electric power and many other technologies have become dependent on super-accurate clocks. Scientific research and the demands of modern technology continue to drive our search for ever more accurate clocks. The next generation of cesium time standards is presently under development at NIST's Boulder laboratory and other laboratories around the world. Atomic Clock, Time Scale, and Time Zone In the 1840s, a Greenwich standard time for all of England, Scotland, and Wales was established, replacing several "local time" systems. The Royal Greenwich Observatory was the focal point for this development because it had played such a key role in marine navigation based upon accurate timekeeping. Greenwich Mean Time (GMT) subsequently evolved as the official time reference for the world and served that purpose until 1972. The United States established the U.S. Naval Observatory (USNO) in 1830 to cooperate with the Royal Greenwich Observatory and other world observatories in determining time based on astronomical observations. The early timekeeping of these observatories was still driven by navigation. Timekeeping had to reflect changes in the earth's rotation rate; otherwise navigators would make errors. Thus, the USNO was charged with providing time linked to "earth" time, and other services, including almanacs, necessary for sea and air navigation. With the advent of highly accurate atomic clocks, scientists and technologists recognized the inadequacy of timekeeping based on the motion of the earth which
fluctuates in rate by a few thousandths of a second a day. The redefinition of the second in 1967 had provided an excellent reference for more accurate measurement of time intervals, but attempts to couple GMT (based on the earth's motion) and this new definition proved to be highly unsatisfactory. A compromise time scale was eventually devised, and on January 1, 1972, the new Coordinated Universal Time (UTC) became effective internationally. UTC runs at the rate of the atomic clocks, but when the difference between this atomic time and one based on the earth approaches one second, a one-second adjustment (a "leap second") is made in UTC. The National Institute of Standards and Technology's clock systems and other atomic clocks located in more than 25 countries now contribute data to the international UTC scale coordinated in Paris by the International Bureau of Weights and Measures (BIPM). An evolution in timekeeping responsibility from the observatories of the world to the measurement standards laboratories has naturally accompanied this change from "earth" time to "atomic" time. But there is still a needed coupling, the leap second, between the two. The World's Time Zones Time zones did not become necessary in the United States until trains made it possible to travel hundreds of miles in a day. Until the 1860s most cities relied upon their own local "sun" time, but this time changed by approximately one minute for every 12 1/2 miles traveled east or west. The problem of keeping track of over 300 local times was overcome by establishing railroad time zones. Standard time zones were first invented by Scottish-Canadian, railroad engineer, Sir Sandford Fleming in 1878, and universally accepted in 1884. However, until 1883 most railway companies relied on some 100 different, but consistent, time zones. That year, the United States was divided into four time zones roughly centered on the 75th, 90th, 105th, and 120th meridians. At noon, on November 18, 1883, telegraph lines transmitted GMT time to major cities where authorities adjusted their clocks to their zone's proper time. On November 1, 1884, the International Meridian Conference in Washington, DC, applied the same procedure to zones all around the world. The 24 standard meridians, every 15° east and west of 0° at Greenwich, England, were designated the centers of the zones. The international dateline was drawn to generally follow the 180° meridian in the Pacific Ocean. Because some countries, islands and states do not want to be divided into several zones, the zones' boundaries tend to wander considerably from straight north-south lines.
Types of Clocks: There are many types of clocks the most important types of them are:
THE ALARM CLOCK History of the Alarm Clock: The first mechanical clocks were made in the 14th century, and were large monumental clocks. Household clocks were in use by 1620 and some of them had alarm mechanisms. The alarm is simple in concept, typically having a cam that rotates every 12 hours. It has a notch into which a lever can fall, releasing a train of gears that drives a hammer, which repeatedly hits a bell until it runs down or is shut off (many alarms have no shutoff control). The earliest alarm clock I found reference to is a German iron wall clock with a bronze bell, probably made in Nuremberg in the 15th century. This clock is 19 inches tall and of open framework construction. It needed to hang high on the wall to make room for the driving weight to fall. Other alarm clocks from the 1500's are in existence. See “The Clockwork Universe, German Clocks and Automata 1550 - 1650,” Maurice and Mayr, 1980, Smithsonian, Neale Watson Academic Publications, New York. The book “Early English Clocks” by Dawson, Drover and Parkes, Antique Collectors Club, 1982, documents some early alarm clocks. An example is a lantern clock ca. 1620 that has an alarm set disc on front of the dial. One long case (grandfather) clock ca. 1690 is documented, as is a 30 hour hanging timepiece alarm by Joseph Knibb. English clockmakers immigrated to the United States in the 18th century and no doubt carried the idea of the alarm clock with them. It has been said that Levi Hutchins of Concord, New Hampshire invented the first alarm clock in 1787. He may have made an early American alarm clock, but his clock was predated by the German and English ones mentioned above. Simon Willard of Grafton, Massachusetts, made alarm time timepieces sometimes called “lighthouse clocks” in the 1820's. Some of the American wooden works shelf clocks of the 1820's - 30's have alarms, as do many brass movement shelf clocks after 1840. Seth Thomas Clock Company was granted a patent in 1876 for a small bedside alarm clock. This may have been the first clock of this type, or perhaps other makers were working on this idea at the same time. In the
late 1870's, small alarm clocks became popular, and the major US clock companies started making them, followed by the German clock companies. The predecessor of Westclox was founded in 1885 with an improved method of small clock construction. Westclox introduced the Chime Alarm in 1931. This clock was advertised with the slogan “First he whispers, and then he shouts.� The Westclox Moonbeam was introduced in 1949. This clock's alarm flashes a light on and off, and then a buzzer sounds. Westclox now sells an excellent reproduction of the Moonbeam. General Electric-Telechron first marketed a snooze alarm in 1956. The first Westclox Drowse (snooze) electric alarms were sold in 1959 and could be set for five (5) or ten (10) minutes snooze time. Modern Clock Trivia In 1577, Jost Burgi invented the minute hand. Burgi's invention was part of a clock made for Tycho Brahe, an astronomer who needed an accurate clock for his stargazing. In 1656, the pendulum was invented by Christian Huygens, making clocks more accurate. In 1504, the first portable (but not very accurate) timepiece was invented in Nuremberg, Germany by Peter Heinlein. The first reported person to actually wear a watch on the wrist was the French mathematician and philosopher, Blaise Pascal (1623-1662). With a piece of string, he attached his pocket watch to his wrist. The word 'clock' comes from the French word "cloche" meaning bell. The Latin for bell is glocio, the Saxon is clugga and the German is glocke. Sir Sanford Fleming invented standard time in 1878. An early prototype of the alarm clock was invented by the Greeks around 250 BC. The Greeks built a water clock where the raising waters would both keep time and eventually hit a mechanical bird that triggered an alarming whistle. The first mechanical alarm clock was invented by Levi Hutchins of Concord, New Hampshire, in 1787. However, the ringing bell alarm on his clock could ring only at 4 am. On October 24, 1876 a mechanical wind-up alarm clock that could be set for any time was patented (#183,725) by Seth E Thomas. Swiss John Harwood invented the self-winding watch in 1923.
The mechanical components of the alarm clock
THE Watch A watch A watch is a small portable clock that displays the time and sometimes the day, date, month and year. In modern times they are usually worn on the wrist with a watch-strap (made of e.g. leather (often synthetic), metal, or nylon), although before the 20th century most were pocket watches, which had covers and were carried separately, often in a pocket, and hooked to a watch chain. Current watches are often digital watches, using a piezoelectric crystal, usually quartz, as an oscillator (see quartz clock). Mechanical timepieces are still used, usually powered by a spring wound regularly by the user, e.g. a stem winder. The invention of "Automatic" or "Self-Winding" watches allowed for a constant winding without special action from the wearer: it works by an eccentric weight, called a winding rotor, that rotates to the movement of the wearer's body. The back-andforth motion of the winding rotor couples to a ratchet to automatically wind the watch. Watches may be collectible; they are often made of precious metals, and can be considered an article of jewelry.
Types of watch 1) Pocket clock The earliest need for portability in time keeping was navigation and mapping in the 15th century. The latitude could be measured by looking at the stars, but the only way a ship could measure its longitude was by comparing timezones; by comparing the midday time of the local longitude to a European meridian (usually Paris or Greenwich), a sailor could know how far he was from home. However, the process was notoriously unreliable until the introduction of John Harrison's chronometer. For that reason, most maps from the 15th century to c.1800 have precise latitudes but distorted longitudes. The first reasonably accurate mechanical clocks measured time with weighted pendulums, which are useless at sea or in watches. The invention of a spring mechanism was crucial for portable clocks. In Tudor England,
the development of "pocket-clockes" was enabled through the development of reliable springs and escapement mechanisms, which allowed clockmakers to compress a timekeeping device into a small, portable compartment. In 1524, Peter Henlein created the first pocket watch[1][2]. It is rumoured that Henry VIII (the portrait of Henry VIII at this link shows the medallion thought to be the back of his watch) had a pocket clock which he kept on a chain around his neck. However, these watches only had an hour hand - a minute hand would have been useless considering the inaccuracy of the watch mechanism. Eventually, miniaturization of these spring-based designs allowed for accurate portable timepieces which worked well even at sea. Aaron Lufkin Dennison founded Waltham Watch Company in 1850, which was the pioneer of the industrial manufacturing by interchangeable parts, the American System of Watch Manufacturing.
2) Wrist watch Breitling Navitimer Montbrillant, a typical pilot watch. Quantum on hand, day of the week, month, slide rule, chronometer certified. The wristwatch was invented by Patek Philippe at the end of the 19th century. It was however considered a woman's accessory. It was not until the beginning of the 20th century that the Brazilian inventor Alberto Santos-Dumont, who had difficulty checking the time while in his first aircraft (Dumont was working on the invention of the aeroplane), asked his friend Louis Cartier for a watch he could use more easily. Cartier gave him a leather-band wristwatch from which Dumont never separated. Being a popular figure in Paris, Cartier was soon able to sell these watches to other men. During the First World War, officers in all armies soon discovered that in battlefield situations, quickly glancing at a watch on their wrist were far more convenient than fumbling in their jacket pockets for an old-fashioned pocket watch. In addition, as increasing numbers of officers were killed in the early stages of the war, NCOs promoted to replace them often did not have pocket watches (traditionally a middle-class item out of the reach of ordinary working-class soldiers), and so relied on the army to provide them with timekeepers. As the scale of battles increased, artillery and infantry officers were required to synchronize watches in order to conduct attacks at precise moments, whilst artillery officers were in need of a large number of accurate timekeepers for rangefinding and gunnery. Army contractors began to
issue reliable, cheap, mass-produced wristwatches which were ideal for these purposes. When the war ended, demobilized European and American officers were allowed to keep their wristwatches, helping to popularize the items amongst middle-class Western civilian culture. Today, many Westerners wear watches on their wrist, a direct result of the First World War.
3) Complicated watch A complicated watch has one or more functionalities beyond basic timekeeping capabilities; such functionality is called a complication. Two popular complications are the chronograph complication, which is the ability of the watch movement to function as a stopwatch, and the moonphase complication, which is a display of the lunar phase. Among watch enthusiasts, complicated watches are especially collectible.
4) Chronograph and chronometer The similar-sounding terms chronograph and chronometer are often confused, although they mean altogether different things. A chronograph is a type of complication, as explained under the heading "Complicated Watch." A chronometer is a watch or clock whose movement has been tested and certified to operate within a certain standard of accuracy by the COSC (Contrôle Officiel Suisse des Chronomètres). The concepts are different but not mutually exclusive; a watch can be a chronograph, a chronometer, both, or neither.
5) Electromechanical watch The first use of electrical power in watches was as a source of energy to replace the mainspring, and therefore to remove the need for winding. The first battery-powered watch, the Hamilton Electric 500, was released in 1957 by the Hamilton Watch Company of Lancaster, Pennsylvania.
6) Quartz analog watch The quartz analog watch is an electronic watch that uses a piezoelectric quartz crystal as its timing element, coupled to a mechanical movement that drives the hands. The first prototypes 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. There are
also several variations of the quartz watch as to what actually powers the movement. There are solar powered, kinetically powered, battery powered and other less common power sources. Solar powered quartz watches are powered by available light. Kinetic powered quartz watches make use of the motion of the wearer's arm turning a rotating weight, which in turn, turns a generator to supply power. A seldom used power source is temperature difference between the wearer's arm and the surrounding environment (as applied in the Citizen Eco Drive Thermo). The most common power source is the battery. Watch batteries come in many forms, the most common of which are silver oxide and lithium. 7) Digital watch Cheaper electronics permitted the popularization of the digital watch (an electronic watch with a numerical, rather than analog, display) in the second half of the 20th century. They were seen as the great new thing. Douglas Adams, in the introduction of his novel The Hitchhiker's Guide to the Galaxy, would say that humans were 'so amazingly primitive that they still think digital watches are a pretty neat idea'. The first digital watch, a Pulsar prototype in 1970, was developed jointly by Hamilton Watch Company and Electro-Data. A retail version of the Pulsar was put on sale in 1972. It had a red light-emitting diode (LED) display. LED displays were soon superseded by liquid crystal displays (LCDs), which used less battery power. The first LCD watch with a six-digit LCD was the 1973 Seiko 06LC, although various forms of early LCD watches with a fourdigit display were marketed as early as 1972 including the 1972 Gruen Teletime LCD Watch [3], [4]. In addition to the function of a timepiece, digital watches can have additional functions like a chronograph, calculator, video game, etc. Digital watches have not replaced analog watches, despite their greater reliability and lower cost. In fact, because digital watches are so cheap, analog watches are often worn as status symbols. For others, analog watches are just easier to read.
8) Fashionable watch At the end of the 20th century, Swiss watch makers were seeing their sales go down as analog clocks were considered obsolete. They joined forces with designers from many countries to reinvent the Swiss watch. The result was that they could considerably reduce the pieces and production time of an analog watch. In fact it was so cheap that if a watch
broke it would be cheaper to throw it away and buy a new one than to repair it. They founded the Swiss Watch company (Swatch) and called graphic designers to redesign a new annual collection. This is often used as a case study in design schools to demonstrate the commercial potential of industrial and graphic design. 9) Advanced watch In 1990 radio controlled wristwatches or as they are sometimes called "atomic watches" reached the market. These wristwatches normally receive a radio signal from one of the national atomic clock facilities around the world, for example the National Institute of Standards and Technology located in Colorado in the United States. This radio signal tells the wristwatch exactly what time it is, in theory precise to a fraction of a nanosecond. It will also reset itself when daylight saving time changes. Similar signals are broadcast from Rugby, England and Frankfurt, Germany. In recent years, mass production has meant that atomic watches have become as cheap as quartz watches, though market share still remains small as interest from big manufacturers is limited. Other technological enhancements to wristwatches have been explored but most of them remained unnoticed. In 2005 for example, a company has put into market an alarm wristwatch with an accelerometer inside that monitors the user's sleep and rings during one of his almost-awake phases. A number of functionalities non directly related to time have also been inserted into watches. As miniaturized electronics become cheaper, watches have been developed containing calculators, video games, digital cameras, keydrives, GPS receivers and cellular phones. In the early 1980s Seiko marketed a watch with a television receiver in it, although at the time television receivers were too bulky to fit in a wristwatch, and the actual receiver and its power source were in a book-sized box with a cable that ran to the wristwatch. In the early 2000s, a self-contained wristwatch television receiver came on the market, with a strong enough power source to provide one hour of viewing. These watches have not had sustained long-term sales success. As well as awkward user interfaces due to the tiny screens and buttons possible in a wearable package, and in some cases short battery life, the functionality available has not generally proven sufficiently compelling to attract buyers. Such watches have also had the reputation as ugly and thus mainly geek toys. Now with the ubiquity of the mobile phone in many countries, which have bigger screens, buttons, and batteries, interest in incorporating extra functionality in watches seems to have declined. Several companies have however attempted to develop a computer contained in a WristWatch (see also wearable computer). As of 2005, the
only programmable computer watches to have made it to market are the Seiko Ruputer, the Matsucom onHand, and the Fossil, Inc. WristPDA, although many digital watches come with extremely sophisticated data management software built in.
The Atomic clock
Atomic clock
Chip-Scale Atomic Clock Unveiled by NIST
An atomic clock is a type of clock that uses an atomic resonance frequency standard as its counter. Early atomic clocks were masers with attached equipment. Today’s best atomic frequency standards (or clocks) are based on more advanced physics involving cold atoms and atomic fountains. National standards agencies maintain an accuracy of 10-9 seconds per day, and a precision equal to the frequency of the radio transmitter pumping the maser. The clocks maintain a continuous and stable time scale, International Atomic Time (TAI). For civil time, another time scale is disseminated, Coordinated Universal Time (UTC). UTC is derived from TAI, but synchronized with the passing of day and night based on astronomical observations. The first atomic clock was built in 1949 at the U.S. National Bureau of Standards. The first accurate atomic clock, based on the transition of the caesium-133 atom, was built by Louis Essen in 1955 at the National Physical Laboratory in the UK. This led to the internationally agreed definition of the second being based on atomic time. In August 2004, NIST scientists demonstrated a chip-scaled atomic clock. According to the researchers, the clock was believed to be one hundredth the size of any other. It was also claimed that it requires just 75 mW, making it suitable for battery-driven applications.
Modern radio clocks are referenced to atomic clocks, and provide a way of getting high-quality atomic-derived time over a wide area using inexpensive equipment; however, radio clocks are not appropriate for highprecision, scientific work.
How they work Frequency reference masers use glowing chambers of ionized gas, most often caesium, because caesium is the element used in the official international definition of the second. Since 1967, the International System of Units (SI) has defined the second as 9,192,631,770 cycles of the radiation which corresponds to the transition between two energy levels of the ground state of the Caesium133 atom. This definition makes the caesium oscillator (often called an atomic clock) the primary standard for time and frequency measurements (see caesium standard). Other physical quantities, like the volt and metre, rely on the definition of the second as part of their own definitions. The core of the atomic clock is a microwave cavity containing the ionized gas, a tunable microwave radio oscillator, and a feedback loop which is used to adjust the oscillator to the exact frequency of the absorption characteristic defined by the behavior of the individual atoms. The microwave transmitter fills the chamber with a standing wave of radio waves. When the radio frequency matches the hyperfine transition frequency of caesium, the caesium atoms absorb the radio waves and emit light. The radio waves make the electrons move farther from their nuclei. When the electrons are attracted back closer by the opposite charge of the nucleus, the electrons wiggle before they settle down in their new location. This moving charge causes the light, which is a wave of alternating electricity and magnetism. A photocell looks at the light. When the light gets dimmer because the frequency of the excitation has drifted from the true resonance frequency, electronics between the photocell and radio transmitter adjusts the frequency of the radio transmitter. This adjustment process is where most of the work and complexity of the clock lies. The adjustment tries to eliminate unwanted side-effects, such as frequencies from other electron transitions, distortions in quantum fields and temperature effects in the mechanisms. For example, the radio wave’s frequency could be deliberately cycled sinusoidally up and down to generate a modulated signal at the photocell. The photocell’s signal can then be demodulated to apply feedback to control long-term drift in the radio frequency. In this way, the ultra-precise quantum-mechanical
properties of the atomic transition frequency of the caesium can be used to tune the microwave oscillator to the same frequency (except for a small amount of experimental error). In practice, the feedback and monitoring mechanism is much more complex than described above. When a clock is first turned on, it takes a while for it to settle down before it can be trusted. A counter counts the waves made by the radio transmitter. A computer reads the counter, and does math to convert the number to something that looks like a digital clock, or a radio wave that is transmitted. Of course, the real clock is the original mechanism of cavity, oscillator and feedback loop that maintains the frequency standard on which the clock is based. A number of other atomic clock schemes are in use for other purposes. Rubidium clocks are prized for their low cost, small size (commercial standards are as small as 400 cm3), and short term stability. They are used in many commercial, portable and aerospace applications. Hydrogen masers (often manufactured in Russia) have superior short term stability to other standards, but lower long term accuracy. Often, one standard is used to fix another. For example, some commercial applications use a Rubidium standard slaved to a GPS receiver. This achieves excellent short term accuracy, with long term accuracy equal to (and traceable to) the U.S. national time standards. The lifetime of a standard is an important practical issue. Modern Rubidium standard tubes last more than ten years, and can cost as little as $50 US. Caesium reference tubes suitable for national standards currently last about seven years, and cost about $35,000 US. Hydrogen standards have an unlimited lifetime.
Research Most research focuses on way to make the clocks smaller, cheaper, more accurate, and more reliable. These goals usually conflict. A lot of research currently focuses on various sorts of ion traps. Theoretically, a single ion suspended electromagnetically could be observed for very long periods, increasing the accuracy of the clock, while also reducing its size and power consumption. In practice, single-ion clocks have poor short term accuracy because the ion moves so much. Current research uses laser cooling of ions, with optical resonators to increase the short term stability of the driving optics. Much of the difficulty is related to eliminating temperature and mechanical noise effects in the resonators and lasers. No laser has achieved wide use.
The result is that the ion trap is very small, but the supporting equipment is still large. Some researchers developed clocks with different geometries of ion traps, as well. Linear clouds of ions usually have better short term accuracy than single ions. There are trade-offs. The best developed systems use Mercury ions. Some researchers experiment with other ions. A particular isotope of Ytterbium has a particularly precise resonant frequency in one of its hyperfine transitions. Strontium has a hyperfine transition that is not as precise, but can be driven by solid-state lasers. This might permit a very inexpensive, longlasting compact clock. AND THERE IS A LOT OF OTHER TYPES OF CLOCKS AS : Ogee clock Nuclear clock Long case clock
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From the early sundials, to the modern day atomic clocks, clocks have had very little impact on the environment as they mostly depend on electricity and burn no fuel. Clocks have significantly led to an increase in productivity as they helped regulate working hours and measure things such as machining times and machine speeds that would greatly help in the automation of many manufacturing processes and thus increase not only the productivity but the quality of products. As to the effect that clocks have had on our civilization, there can be no doubt that they’ve introduced a lot of concepts into our lives: most obviously, the concept of time. To be able to conceive of time as a succession of events and as a measurable quantity was a milestone of human civilization and helped spark a lot of scientific discoveries later. But more importantly clocks have helped the advancement of life in the Ancient Times. Having an objective standard with which to measure time, men could communicate more easily, document events more accurately and measure time rates, speeds, etc… Thus was born a science like mechanics for example. Socially, the clocks affect our daily life, because they keep us aware of what little time we have to accomplish what we set out to do; and in an age like ours, where time is everything, it’s not so strange that clocks are so vitally important that the French poet Baudelaire has written a poem about his fear of the clock!