Quartz clock
Encyclopedia
Clock
A clock is an instrument used to indicate, keep, and co-ordinate time. The word clock is derived ultimately from the Celtic words clagan and clocca meaning "bell". A silent instrument missing such a mechanism has traditionally been known as a timepiece...
that uses an electronic oscillator
Electronic oscillator
An electronic oscillator is an electronic circuit that produces a repetitive electronic signal, often a sine wave or a square wave. They are widely used in innumerable electronic devices...
that is regulated by a quartz crystal to keep time. This crystal oscillator
Crystal oscillator
A crystal oscillator is an electronic oscillator circuit that uses the mechanical resonance of a vibrating crystal of piezoelectric material to create an electrical signal with a very precise frequency...
creates a signal with very precise frequency
Frequency
Frequency is the number of occurrences of a repeating event per unit time. It is also referred to as temporal frequency.The period is the duration of one cycle in a repeating event, so the period is the reciprocal of the frequency...
, so that quartz clocks are at least an order of magnitude more accurate than good mechanical clocks. Generally, some form of digital logic counts the cycles of this signal and provides a numeric time
Time
Time is a part of the measuring system used to sequence events, to compare the durations of events and the intervals between them, and to quantify rates of change such as the motions of objects....
display, usually in units of hours, minutes, and seconds. Quartz timekeepers are the world's most widely-used timekeeping technology, used in most clocks and watch
Watch
A watch is a small timepiece, typically worn either on the wrist or attached on a chain and carried in a pocket, with wristwatches being the most common type of watch used today. They evolved in the 17th century from spring powered clocks, which appeared in the 15th century. The first watches were...
es, as well as computers and other appliances that keep time.
Explanation
Chemically, quartz is a compound called silicon dioxideSilicon dioxide
The chemical compound silicon dioxide, also known as silica , is an oxide of silicon with the chemical formula '. It has been known for its hardness since antiquity...
. When a crystal of quartz is properly cut and mounted, it can be made to vibrate, or oscillate, using an alternating electric current; each oscillation, in turn, causes a voltage change across the crystal, which can be detected by a suitable electronic circuit. The frequency at which the crystal oscillates is dependent on its shape and size, and the positions at which electrodes are placed on it. If the crystal is accurately shaped and positioned, it will oscillate at a desired frequency; in clocks and watches, the frequency is usually 32,768 Hz, as a crystal for this frequency is conveniently small, and as this frequency is a power of two and can easily be counted using a 15-bit binary digital counter. Once the circuit supplying power to the crystal counts that this number of oscillations have occurred, it increases the recorded time by one second. This property, of generating an electric current upon the application of mechanical pressure, and vice versa, is known as piezoelectricity
Piezoelectricity
Piezoelectricity is the charge which accumulates in certain solid materials in response to applied mechanical stress. The word piezoelectricity means electricity resulting from pressure...
(direct and converse). Such crystals were once used in low-end phonograph
Phonograph
The phonograph record player, or gramophone is a device introduced in 1877 that has had continued common use for reproducing sound recordings, although when first developed, the phonograph was used to both record and reproduce sounds...
cartridges: the movement of the stylus (needle) would flex a quartz crystal, which would produce a small voltage, which was amplified and played through speakers.
Many materials can be formed into plates that will resonate. However, since quartz can be directly driven (to flex) by an electric signal, no additional speaker or microphone is required.
Quartz has the further advantage that its size does not change much as temperature
Temperature
Temperature is a physical property of matter that quantitatively expresses the common notions of hot and cold. Objects of low temperature are cold, while various degrees of higher temperatures are referred to as warm or hot...
fluctuates. Fused quartz
Fused quartz
Fused quartz and fused silica are types of glass containing primarily silica in amorphous form. They are manufactured using several different processes...
is often used for laboratory equipment that must not change shape along with the temperature, because a quartz plate's resonance frequency, based on its size, will not significantly rise or fall. Similarly, a quartz clock will remain relatively accurate as the temperature changes.
Mechanism
In modern quartz clocks, the quartz crystal resonatorResonator
A resonator is a device or system that exhibits resonance or resonant behavior, that is, it naturally oscillates at some frequencies, called its resonant frequencies, with greater amplitude than at others. The oscillations in a resonator can be either electromagnetic or mechanical...
is in the shape of a small tuning fork
Tuning fork
A tuning fork is an acoustic resonator in the form of a two-pronged fork with the prongs formed from a U-shaped bar of elastic metal . It resonates at a specific constant pitch when set vibrating by striking it against a surface or with an object, and emits a pure musical tone after waiting a...
, laser
Laser
A laser is a device that emits light through a process of optical amplification based on the stimulated emission of photons. The term "laser" originated as an acronym for Light Amplification by Stimulated Emission of Radiation...
-trimmed or precision lapped to vibrate at 32,768 Hz
Hertz
The hertz is the SI unit of frequency defined as the number of cycles per second of a periodic phenomenon. One of its most common uses is the description of the sine wave, particularly those used in radio and audio applications....
. 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
High frequency
High frequency radio frequencies are between 3 and 30 MHz. Also known as the decameter band or decameter wave as the wavelengths range from one to ten decameters . Frequencies immediately below HF are denoted Medium-frequency , and the next higher frequencies are known as Very high frequency...
crystals, which reduces the life of the watch battery. During the 1970s, the introduction of metal–oxide–semiconductor
MOSFET
The metal–oxide–semiconductor field-effect transistor is a transistor used for amplifying or switching electronic signals. The basic principle of this kind of transistor was first patented by Julius Edgar Lilienfeld in 1925...
(MOS) integrated circuit
Integrated circuit
An integrated circuit or monolithic integrated circuit is an electronic circuit manufactured by the patterned diffusion of trace elements into the surface of a thin substrate of semiconductor material...
s allowed a 12-month battery life from a single coin cell when driving either a mechanical stepper motor
Stepper motor
A stepper motor is a brushless, electric motor that can divide a full rotation into a large number of steps. The motor's position can be controlled precisely without any feedback mechanism , as long as the motor is carefully sized to the application...
, indexing the second hand (in a quartz analog watch), or a liquid crystal display
Liquid crystal display
A liquid crystal display is a flat panel display, electronic visual display, or video display that uses the light modulating properties of liquid crystals . LCs do not emit light directly....
(in an LCD digital watch). Light-emitting diode
Light-emitting diode
A light-emitting diode is a semiconductor light source. LEDs are used as indicator lamps in many devices and are increasingly used for other lighting...
(LED) displays for watches have become rare due to their comparatively high battery consumption.
The basic formula for calculating the fundamental frequency
Fundamental frequency
The fundamental frequency, often referred to simply as the fundamental and abbreviated f0, is defined as the lowest frequency of a periodic waveform. In terms of a superposition of sinusoids The fundamental frequency, often referred to simply as the fundamental and abbreviated f0, is defined as the...
(f) of vibration of a cantilever
Cantilever
A cantilever is a beam anchored at only one end. The beam carries the load to the support where it is resisted by moment and shear stress. Cantilever construction allows for overhanging structures without external bracing. Cantilevers can also be constructed with trusses or slabs.This is in...
as a function of its dimensions (quadratic cross-section) is:
where
- 1.875 the smallest positive solution of cos(x)cosh(x) = -1
- l is the length of the cantilever
- a is its thickness along the direction of motion
- E is its Young's modulusYoung's modulusYoung's modulus is a measure of the stiffness of an elastic material and is a quantity used to characterize materials. It is defined as the ratio of the uniaxial stress over the uniaxial strain in the range of stress in which Hooke's Law holds. In solid mechanics, the slope of the stress-strain...
- and ρ is its densityDensityThe mass density or density of a material is defined as its mass per unit volume. The symbol most often used for density is ρ . In some cases , density is also defined as its weight per unit volume; although, this quantity is more properly called specific weight...
A cantilever made of quartz
Quartz
Quartz is the second-most-abundant mineral in the Earth's continental crust, after feldspar. It is made up of a continuous framework of SiO4 silicon–oxygen tetrahedra, with each oxygen being shared between two tetrahedra, giving an overall formula SiO2. There are many different varieties of quartz,...
(E = 1011 N·m−2 = 100 GPa
Pascal (unit)
The pascal is the SI derived unit of pressure, internal pressure, stress, Young's modulus and tensile strength, named after the French mathematician, physicist, inventor, writer, and philosopher Blaise Pascal. It is a measure of force per unit area, defined as one newton per square metre...
and ρ = 2634 kg
Kilogram
The kilogram or kilogramme , also known as the kilo, is the base unit of mass in the International System of Units and is defined as being equal to the mass of the International Prototype Kilogram , which is almost exactly equal to the mass of one liter of water...
·m-3 )
with a length of 3 mm and a thickness of 0.3 mm has thus a fundamental frequency of around 33 kHz.
The crystal is tuned to exactly 215 = 32,768 Hz or runs at a slightly higher frequency with inhibition compensation (see below).
Accuracy
The relative stability of the 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 at 31 °C (87.8 °F): that is, a typical quartz wristwatch will gain or lose less than a half second per day at body temperature.If a quartz wristwatch is "rated" by measuring its timekeeping characteristics against an atomic clock
Atomic clock
An atomic clock is a clock that uses an electronic transition frequency in the microwave, optical, or ultraviolet region of the electromagnetic spectrum of atoms as a frequency standard for its timekeeping element...
's time broadcast, to determine how much time the watch gains or loses per day, and adjustments are made to the circuitry to "regulate" the timekeeping, then the corrected time will easily be accurate within 10 seconds per year. This is more than adequate to perform celestial navigation
Celestial navigation
Celestial navigation, also known as astronavigation, is a position fixing technique that has evolved over several thousand years to help sailors cross oceans without having to rely on estimated calculations, or dead reckoning, to know their position...
.
Some premium clock designs self-rate and self-regulate. That is, rather than just counting vibrations, their computer program takes the simple count, and scales it using a ratio calculated between an epoch
Epoch (reference date)
In the fields of chronology and periodization, an epoch is an instance in time chosen as the origin of a particular era. The "epoch" then serves as a reference point from which time is measured...
set at the factory, and the most recent time the clock was set. These clocks usually have special instructions for changing the battery (the counter must not be permitted to stop), and become more accurate as they age.
It is possible for a computerized clock to measure its temperature, and adjust for that as well. Both analog
Analog signal
An analog or analogue signal is any continuous signal for which the time varying feature of the signal is a representation of some other time varying quantity, i.e., analogous to another time varying signal. It differs from a digital signal in terms of small fluctuations in the signal which are...
and digital
Digital
A digital system is a data technology that uses discrete values. By contrast, non-digital systems use a continuous range of values to represent information...
temperature compensation have been used in high-end quartz watches.
Many inexpensive quartz watches use a technique known as inhibition compensation. The crystal is deliberately made to run somewhat fast, and the digital logic is programmed to skip a small number of crystal cycles at regular intervals such as 10 seconds or one minute. The advantage of this method is that after measuring the frequency of each chip with a precision timer at the factory, storing the number of pulses to suppress in a non-volatile memory register on the chip is less expensive than the older technique of trimming the quartz tuning fork frequency. In more expensive watches, thermal compensation can be implemented by varying the number of cycles to inhibit depending on the output from a temperature sensor. Thermo compensated quartz movements, even in wrist watches, can be accurate to within 10 or 20 seconds per year.
Chronometers
Quartz chronometerChronometer
Chronometer may refer to:* Chronometer watch, a watch tested and certified to meet certain precision standards* Hydrochronometer, a water clock* Marine chronometer, a timekeeper used for celestial navigation...
s designed as time standards often include a crystal oven
Crystal oven
A crystal oven is a temperature-controlled chamber used to maintain the quartz crystal in electronic crystal oscillators at a constant temperature, in order to prevent changes in the frequency due to variations in ambient temperature...
, to keep the crystal at a constant temperature. Some self-rate and include "crystal farms," so that the clock can take the average
Average
In mathematics, an average, or central tendency of a data set is a measure of the "middle" value of the data set. Average is one form of central tendency. Not all central tendencies should be considered definitions of average....
of a set of time measurements.
History
Jacques Curie
Paul-Jacques Curie was a French physicist and professor at the University of Montpellier. He and his brother, Pierre Curie, studied pyroelectricity in the 1880s, leading to their discovery of some of the mechanisms behind piezoelectricity....
and Pierre Curie
Pierre Curie
Pierre Curie was a French physicist, a pioneer in crystallography, magnetism, piezoelectricity and radioactivity, and Nobel laureate. He was the son of Dr. Eugène Curie and Sophie-Claire Depouilly Curie ...
in 1880. The first quartz crystal oscillator
Crystal oscillator
A crystal oscillator is an electronic oscillator circuit that uses the mechanical resonance of a vibrating crystal of piezoelectric material to create an electrical signal with a very precise frequency...
was built by Walter G. Cady
Walter Guyton Cady
Dr. Walter Guyton Cady was a noted American physicist and electrical engineer. He was a pioneer in piezoelectricity, and in 1921 developed the first crystal oscillator....
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 next 3 decades saw the development of quartz clocks as precision time standards in laboratory settings; the bulky delicate counting electronics, built with vacuum tube
Vacuum tube
In electronics, a vacuum tube, electron tube , or thermionic valve , reduced to simply "tube" or "valve" in everyday parlance, is a device that relies on the flow of electric current through a vacuum...
s, limited their use elsewhere. In January 1932 a quartz clock was able to measure tiny weekly variations in the rotation rate of the Earth.! The National Bureau of Standards (now NIST) based the time standard of the US on quartz clocks between the 1930s and the 1960s, then it went to atomic clocks. The wider use of quartz clock technology had to await the development of cheap semiconductor
Semiconductor
A semiconductor is a material with electrical conductivity due to electron flow intermediate in magnitude between that of a conductor and an insulator. This means a conductivity roughly in the range of 103 to 10−8 siemens per centimeter...
digital logic in the 60s.
The world's first protoype analog quartz wristwatches
Watch
A watch is a small timepiece, typically worn either on the wrist or attached on a chain and carried in a pocket, with wristwatches being the most common type of watch used today. They evolved in the 17th century from spring powered clocks, which appeared in the 15th century. The first watches were...
were revealed in 1967: the Beta 1 revealed by the Centre Electronique Horloger (CEH) in Neuchâtel Switzerland, and the prototype of the Astron
Astron (wristwatch)
The Astron wristwatch, formally known as the Seiko Quartz-Astron 35SQ, was the world's first "quartz clock" wristwatch, i.e., one based on a quartz crystal oscillator...
revealed by Seiko
Seiko
, more commonly known simply as Seiko , is a Japanese watch company.-History and ongoing developments:The company was founded in 1881, when Kintarō Hattori opened a watch and jewelry shop called in the Ginza area of Tokyo, Japan. Eleven years later, in 1892, he began to produce clocks under the...
in Japan. (Seiko had been working on quartz clocks since 1958).
In 1969, Seiko
Seiko
, more commonly known simply as Seiko , is a Japanese watch company.-History and ongoing developments:The company was founded in 1881, when Kintarō Hattori opened a watch and jewelry shop called in the Ginza area of Tokyo, Japan. Eleven years later, in 1892, he began to produce clocks under the...
produced the world's first commercial quartz wristwatch, the Astron
Astron (wristwatch)
The Astron wristwatch, formally known as the Seiko Quartz-Astron 35SQ, was the world's first "quartz clock" wristwatch, i.e., one based on a quartz crystal oscillator...
. The inherent accuracy and low cost of production has resulted in the proliferation of quartz clocks and watches since that time. By the 1980s, quartz technology had taken over applications such as kitchen timer
Timer
A timer is a specialized type of clock. A timer can be used to control the sequence of an event or process. Whereas a stopwatch counts upwards from zero for measuring elapsed time, a timer counts down from a specified time interval, like an hourglass.Timers can be mechanical, electromechanical,...
s, alarm clock
Alarm clock
An alarm clock is a clock that is designed to make a loud sound at a specific time. The primary use of these clocks is to awaken people from their night's sleep or short naps; they are sometimes used for other reminders as well. To stop the sound, a button or handle on the clock is pressed; but...
s, bank vault time lock
Time lock
A time lock is a part of a locking mechanism commonly found in bank vaults and other high-security containers. The timelock is a timer designed to prevent the opening of the safe or vault until it reaches 0, even if the correct combination are known...
s, and time fuze
Fuze
Fuze Beverage, commercially referred to as just Fuze , is a manufacturer of teas and non-carbonated fruit drinks enriched with vitamins. Currently the brand consists of five vitamin-infused lines: Slenderize, Refresh, Tea, Defensify, and Vitalize...
s on munitions, from earlier mechanical balance wheel
Balance wheel
The balance wheel is the timekeeping device used in mechanical watches and some clocks, analogous to the pendulum in a pendulum clock. It is a weighted wheel that rotates back and forth, being returned toward its center position by a spiral spring, the balance spring or hairspring...
movements.
Many traditional European clockmakers, particularly in Switzerland, Germany, France and Russia have continued to produce the less-accurate but still-popular mechanical watch
Mechanical watch
A mechanical watch is a watch that uses a mechanical mechanism to measure the passage of time, as opposed to modern quartz watches which function electronically. It is driven by a spring which must be wound periodically...
es.
Quartz wristwatches
Watch
A watch is a small timepiece, typically worn either on the wrist or attached on a chain and carried in a pocket, with wristwatches being the most common type of watch used today. They evolved in the 17th century from spring powered clocks, which appeared in the 15th century. The first watches were...
are in high demand today as they are more accurate than their mechanical counterparts; they need neither winding nor much maintenance. Light-powered and motion-powered quartz watches represent two innovative types of timepieces. Light-powered quartz watches incorporate a solar cell that transforms the light into electricity. Motion-powered wristwatches have a tiny rotor spinning in response to motion of the wrist, and generating electricity.
See also
- Automatic quartzAutomatic quartzAutomatic quartz is a collective term describing watch movements that combine a self-winding rotor mechanism to generate electricity with a piezoelectric quartz crystal as its timing element. Such movements aim to provide the advantages of quartz without the environmental impact of batteries...
- Light powered quartz
- Electric watchElectric watchElectric watch, which commonly means any watch that is powered by electricity, has become a generic term for the first generation of electrically powered watches which appeared starting in 1957, before the invention of quartz watches in the 1970s...
- Quartz crisisQuartz crisisThe Quartz Crisis, also known as the Quartz Revolution is a term used in the watchmaking industry to refer to the economic upheavals caused by the advent of quartz watches in the 1970s and early 1980s, which largely replaced mechanical watches...
- German inventors and discoverersGerman inventors and discoverersThis is a list of German inventors and discoverers. The following list comprises people from Germany or German-speaking Europe, also of people of predominantly German heritage, in alphabetical order of the surname. The main section includes existing articles, indicated by blue links, and possibly...