Electric Clock
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An electric clock is a
clock A clock or a timepiece is a device used to measure and indicate time. The clock is one of the oldest human inventions, meeting the need to measure intervals of time shorter than the natural units such as the day, the lunar month and the ...
that is powered by
electricity Electricity is the set of physical phenomena associated with the presence and motion of matter that has a property of electric charge. Electricity is related to magnetism, both being part of the phenomenon of electromagnetism, as described ...
, as opposed to a mechanical clock which is powered by a hanging weight or a
mainspring A mainspring is a spiral torsion spring of metal ribbon—commonly spring steel—used as a power source in mechanical watches, some clocks, and other clockwork mechanisms. ''Winding'' the timepiece, by turning a knob or key, stores energy in ...
. The term is often applied to the electrically powered mechanical clocks that were used before
quartz clock Quartz clocks and quartz watches are timepieces that use an electronic oscillator regulated by a quartz crystal to keep time. This crystal oscillator creates a signal with very precise frequency, so that quartz clocks and watches are at least an ...
s were introduced in the 1980s. The first experimental electric clocks were constructed around the 1840s, but they were not widely manufactured until mains
electric power Electric power is the rate at which electrical energy is transferred by an electric circuit. The SI unit of power is the watt, one joule per second. Standard prefixes apply to watts as with other SI units: thousands, millions and billions o ...
became available in the 1890s. In the 1930s, the synchronous electric clock replaced mechanical clocks as the most widely used type of clock.


Types

Electric clocks can operate by several different types of mechanism: *''Electromechanical clocks'' have a traditional mechanical movement, which keeps time with an oscillating
pendulum A pendulum is a weight suspended from a pivot so that it can swing freely. When a pendulum is displaced sideways from its resting, equilibrium position, it is subject to a restoring force due to gravity that will accelerate it back toward the ...
or
balance wheel A balance wheel, or balance, is the timekeeping device used in mechanical watches and small 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 ...
powered through a
gear train A gear train is a mechanical system formed by mounting gears on a frame so the teeth of the gears engage. Gear teeth are designed to ensure the pitch circles of engaging gears roll on each other without slipping, providing a smooth transmission ...
by a
mainspring A mainspring is a spiral torsion spring of metal ribbon—commonly spring steel—used as a power source in mechanical watches, some clocks, and other clockwork mechanisms. ''Winding'' the timepiece, by turning a knob or key, stores energy in ...
, but use electricity to rewind the mainspring with an
electric motor An electric motor is an Electric machine, electrical machine that converts electrical energy into mechanical energy. Most electric motors operate through the interaction between the motor's magnetic field and electric current in a Electromagneti ...
or
electromagnet An electromagnet is a type of magnet in which the magnetic field is produced by an electric current. Electromagnets usually consist of wire wound into a coil. A current through the wire creates a magnetic field which is concentrated in the ...
. This mechanism is found mostly in antique clocks. *''Electric remontoire clocks'' have gear trains turned by a small spring or weighted lever, called a
remontoire In mechanical horology, a remontoire (from the French ''remonter'', meaning 'to wind') is a small secondary source of power, a weight or spring, which runs the timekeeping mechanism and is itself periodically rewound by the timepiece's main power so ...
, which was wound up more frequently by an electric motor or electromagnet. This mechanism was more accurate than a mainspring, because the frequent winding averaged out variations in the clock's rate caused by the varying force of the spring as it unwound. It was used in precision pendulum clocks, and in automotive clocks until the 1970s. *''Electromagnetic clocks'' keep time with a pendulum or balance wheel, but the pulses to keep it going are not provided by a mechanical movement and
escapement An escapement is a mechanical linkage in mechanical watches and clocks that gives impulses to the timekeeping element and periodically releases the gear train to move forward, advancing the clock's hands. The impulse action transfers energy to ...
linkage, but by
magnetic force In physics (specifically in electromagnetism) the Lorentz force (or electromagnetic force) is the combination of electric and magnetic force on a point charge due to electromagnetic fields. A particle of charge moving with a velocity in an elect ...
from an electromagnet (
solenoid upright=1.20, An illustration of a solenoid upright=1.20, Magnetic field created by a seven-loop solenoid (cross-sectional view) described using field lines A solenoid () is a type of electromagnet formed by a helix, helical coil of wire whose ...
). This was the mechanism used in the first electric clocks, and is found in antique electric pendulum clocks. It is also found in a few modern decorative mantel and desk clocks. *''Synchronous clocks'' rely on the 50 or 60 Hz
utility frequency The utility frequency, (power) line frequency (American English) or mains frequency (British English) is the nominal frequency of the oscillations of alternating current (AC) in a wide area synchronous grid transmitted from a power station to th ...
of the AC
electric power grid An electrical grid is an interconnected network for electricity delivery from producers to consumers. Electrical grids vary in size and can cover whole countries or continents. It consists of:Kaplan, S. M. (2009). Smart Grid. Electrical Power ...
as a timing source, by driving the clock gears with a
synchronous motor A synchronous electric motor is an AC electric motor in which, at steady state, the rotation of the shaft is synchronized with the frequency of the supply current; the rotation period is exactly equal to an integral number of AC cycles. Sync ...
. They essentially count cycles of the power supply. While the actual frequency may vary with loading on the grid, the total number of cycles per 24 hours is maintained rigorously constant, so that these clocks can keep time accurately for long periods, barring
power cut A power outage (also called a powercut, a power out, a power failure, a power blackout, a power loss, or a blackout) is the loss of the electrical power network supply to an end user. There are many causes of power failures in an electricity ...
s; over months they are more accurate than a typical quartz clock. This was the most common type of clock from the 1930s but has now been mostly replaced by quartz clocks. *''Tuning Fork clocks'' keep time by counting the oscillations of a calibrated tuning fork with a specific frequency. These were only made in battery-powered form. Battery-powered clocks have been made using the schemes above with the obvious exception of a synchronous movement. All battery-powered clocks have been largely replaced by the lower cost quartz movement. *''
Quartz clock Quartz clocks and quartz watches are timepieces that use an electronic oscillator regulated by a quartz crystal to keep time. This crystal oscillator creates a signal with very precise frequency, so that quartz clocks and watches are at least an ...
s'' are electric clocks which keep time by counting oscillations of a vibrating
quartz crystal Quartz is a hard, crystalline mineral composed of silica (silicon dioxide). The atoms are linked in a continuous framework of SiO4 silicon-oxygen tetrahedra, with each oxygen being shared between two tetrahedra, giving an overall chemical form ...
. They use modern low-voltage DC-powered circuitry, which may be supplied by a battery or derived from mains electricity. They are the most common type of clock today. Quartz clocks and watches as supplied by the manufacturer typically keep time with an error of a few seconds per week, although sometimes more. Inexpensive quartz movements are often specified to keep time within 30 seconds per month (1 second per day, 6 minutes per year). Lower error can be achieved by individual calibration if adjustment is possible, subject to the stability of the oscillator, particularly with change in temperature. Higher accuracy is possible at higher cost. *''
Radio-controlled clock A radio clock or radio-controlled clock (RCC), and often (incorrectly) referred to as an atomic clock is a type of quartz clock or watch that is automatically synchronized to a time code transmitted by a radio transmitter connected to a time st ...
s'' are quartz clocks which are periodically synchronized with the UTC
atomic clock An atomic clock is a clock that measures time by monitoring the resonant frequency of atoms. It is based on atoms having different energy levels. Electron states in an atom are associated with different energy levels, and in transitions betwee ...
time scale via
radio time signal A time signal is a visible, audible, mechanical, or electronic signal used as a reference to determine the time of day. Church bells or voices announcing hours of prayer gave way to automatically operated chimes on public clocks; however, aud ...
s broadcast by dedicated stations around the world. They are distinct from
clock radio An alarm clock (or sometimes just an alarm) is a clock that is designed to alert an individual or group of individuals at a specified time. The primary function of these clocks is to awaken people from their night's sleep or short naps; they ar ...
s.


History

In 1814,
Sir Francis Ronalds Sir Francis Ronalds FRS (21 February 17888 August 1873) was an English scientist and inventor, and arguably the first electrical engineer. He was knighted for creating the first working electric telegraph over a substantial distance. In 1816 ...
of London invented the first electric clock. It was powered with
dry pile upright=1.2, Schematic diagram of a copper–zinc voltaic pile. The copper and zinc discs were separated by cardboard or felt spacers soaked in salt water (the electrolyte). Volta's original piles contained an additional zinc disk at the bottom, ...
s, a high voltage battery with extremely long life but the disadvantage of its electrical properties varying with the weather. He trialled various means of regulating the electricity and these models proved to be reliable across a range of meteorological conditions. In 1815, Giuseppe Zamboni of Verona invented and showed another electrostatic clock run with
dry pile upright=1.2, Schematic diagram of a copper–zinc voltaic pile. The copper and zinc discs were separated by cardboard or felt spacers soaked in salt water (the electrolyte). Volta's original piles contained an additional zinc disk at the bottom, ...
batteries and an oscillating orb. His team produced improved clocks over many years, which were later denoted as "the most elegant and at the same time the most simple movement yet produced by the electric column". Zamboni's clock had a vertical needle supported by a pivot and was so energy efficient that it could operate on one battery for over 50 years. In 1840, Alexander Bain, a Scottish clock and instrument maker was the first to invent and patent a clock powered by electric current. His original electric clock patent is dated October 10, 1840. On January 11, 1841, Alexander Bain along with John Barwise, a chronometer maker, took out another important patent describing a clock in which an
electromagnetic In physics, electromagnetism is an interaction that occurs between particles with electric charge. It is the second-strongest of the four fundamental interactions, after the strong force, and it is the dominant force in the interactions of a ...
pendulum A pendulum is a weight suspended from a pivot so that it can swing freely. When a pendulum is displaced sideways from its resting, equilibrium position, it is subject to a restoring force due to gravity that will accelerate it back toward the ...
and an
electric current An electric current is a stream of charged particles, such as electrons or ions, moving through an electrical conductor or space. It is measured as the net rate of flow of electric charge through a surface or into a control volume. The moving pa ...
is employed to keep the clock going instead of springs or weights. Later patents expanded on his original ideas. Numerous people were intent on inventing the electric clock with electromechanical and electromagnetic designs around the year 1840, such as Wheatstone, Steinheil, Hipp, Breguet, and Garnier, both in Europe and America.
Matthäus Hipp Matthäus Hipp also spelled Matthias or Mathias (Blaubeuren, 25 October 1813 – 3 May 1893 in Fluntern) was a German clockmaker and inventor who lived from 1852 on in Switzerland. His most important, lastingly significant inventions were ele ...
, clockmaker born in
Germany Germany,, officially the Federal Republic of Germany, is a country in Central Europe. It is the second most populous country in Europe after Russia, and the most populous member state of the European Union. Germany is situated betwe ...
, is credited with establishing the production series, mass marketable electric clock. Hipp opened a workshop in
Reutlingen Reutlingen (; Swabian: ''Reitlenga'') is a city in Baden-Württemberg, Germany. It is the capital of the eponymous district of Reutlingen. As of June 2018, it has a population of 115,818. Reutlingen has a university of applied sciences, which ...
, where he developed an electric clock to have the Hipp-Toggle, presented in Berlin at an exhibition in 1843. The Hipp-Toggle is a device attached to a pendulum or balance wheel that electro-mechanically allows occasional impulse or drive to the pendulum or wheel as its amplitude of swing drops below a certain level, and is so efficient that it was subsequently used in electric clocks for over a hundred years. Hipp also invented a small motor and built the chronoscope and the registering
chronograph A chronograph is a specific type of watch that is used as a stopwatch combined with a display watch. A basic chronograph has an independent sweep second hand and a minute sub-dial; it can be started, stopped, and returned to zero by successive ...
for time measurement. The first electric clocks had prominent pendulums because this was a familiar shape and design. Smaller clocks and watches with a spiral-balance are made on the same principles as pendulum clocks. In 1918, Henry Ellis Warren invented the first synchronous electric clock in Ashland, MA, which kept time from the oscillations of the power grid.U.S. patent #1283434
Warren, Henry E. ''Timing device'', filed February 26, 1917, issued October 29, 1918, on Google Patents
In 1931, the Synclock was the first commercial synchronous electric clock sold in the UK.


Electromechanical clock

A clock that employs electricity in some form to power a conventional clock mechanism is an electromechanical clock. Any spring or weight driven clock that uses electricity (either AC or DC) to rewind the spring or raise the weight of a mechanical clock then is an electromechanical clock. In electromechanical clocks the electricity serves no time keeping function. The timekeeping function is regulated by the pendulum. Near the end of the nineteenth century, the availability of the dry cell battery made it practical to use electric power in clocks. The use of electricity then led to many variations of clock and motor designs. Electromechanical clocks were made as individual timepieces but most commonly were used as integral parts of synchronized time installations. Experience in telegraphy led to connecting remote clocks (slave clocks) via wires to a controlling (master clock) clock. The goal was to create a clock system where each clock displayed exactly the same time. The master and the slaves are electromechanical clocks. The
master clock Master or masters may refer to: Ranks or titles * Ascended master, a term used in the Theosophical religious tradition to refer to spiritually enlightened beings who in past incarnations were ordinary humans *Grandmaster (chess), National Master ...
has a conventional self-winding clock mechanism that is rewound electrically. The
slave clock In telecommunication and horology, a slave clock is a clock that depends on another clock, the master clock. Modern clocks are synchronized through the Internet or by radio time signals, to Coordinated Universal Time. UTC is based on a network ...
mechanism is not a conventional clock mechanism as it consists only of a ratchet wheel and time train. Slave clocks rely upon electrical impulses from the master clock to mechanically move the clock hands one unit of time. Synchronized time systems are made up of one master clock and any number of slave clocks. The slave clocks are connected by wires to the master clock. These systems are found in locations where multiple clocks would be used such as learning institutions, businesses, factories, transportation networks, banks, offices and government facilities. A notable example of this type of system is the Shortt-Synchronome clock, which is an example of an electromechanical gravity
remontoire In mechanical horology, a remontoire (from the French ''remonter'', meaning 'to wind') is a small secondary source of power, a weight or spring, which runs the timekeeping mechanism and is itself periodically rewound by the timepiece's main power so ...
. These self-winding clock systems were usually low voltage DC. They were installed through the 1950s and by then systems with synchronous motor clocks were becoming the clock system of choice.


Electromagnetic clock

The configuration of this device is comparatively very simple and reliable. The electric current powers either a
pendulum A pendulum is a weight suspended from a pivot so that it can swing freely. When a pendulum is displaced sideways from its resting, equilibrium position, it is subject to a restoring force due to gravity that will accelerate it back toward the ...
or an
electromechanical In engineering, electromechanics combines processes and procedures drawn from electrical engineering and mechanical engineering. Electromechanics focuses on the interaction of electrical and mechanical systems as a whole and how the two systems ...
oscillator Oscillation is the repetitive or periodic variation, typically in time, of some measure about a central value (often a point of equilibrium) or between two or more different states. Familiar examples of oscillation include a swinging pendulum ...
. The electromechanical oscillator component has an attached
magnet A magnet is a material or object that produces a magnetic field. This magnetic field is invisible but is responsible for the most notable property of a magnet: a force that pulls on other ferromagnetic materials, such as iron, steel, nickel, ...
that passes two
inductors An inductor, also called a coil, choke, or reactor, is a passive two-terminal electrical component that stores energy in a magnetic field when electric current flows through it. An inductor typically consists of an insulated wire wound into a ...
. When the magnet passes the first inductor or sensor, the simple
amplifier An amplifier, electronic amplifier or (informally) amp is an electronic device that can increase the magnitude of a signal (a time-varying voltage or current). It may increase the power significantly, or its main effect may be to boost the v ...
causes the current through the second inductor, and the second inductor works as an
electromagnet An electromagnet is a type of magnet in which the magnetic field is produced by an electric current. Electromagnets usually consist of wire wound into a coil. A current through the wire creates a magnetic field which is concentrated in the ...
, providing an energy pulse to the moving oscillator. This oscillator is responsible for the accuracy of the clock. The electronic part would not generate electrical pulses if the oscillator was absent or did not move. The
resonant Resonance describes the phenomenon of increased amplitude that occurs when the frequency of an applied periodic force (or a Fourier component of it) is equal or close to a natural frequency of the system on which it acts. When an oscilla ...
frequency Frequency is the number of occurrences of a repeating event per unit of time. It is also occasionally referred to as ''temporal frequency'' for clarity, and is distinct from ''angular frequency''. Frequency is measured in hertz (Hz) which is eq ...
of the mechanical oscillator should be several times per second.


Synchronous electric clock

A synchronous electric clock does not contain a timekeeping oscillator such as a pendulum or balance wheel, but instead counts the oscillations of the AC utility current from its wall plug to keep time. It consists of a small AC
synchronous motor A synchronous electric motor is an AC electric motor in which, at steady state, the rotation of the shaft is synchronized with the frequency of the supply current; the rotation period is exactly equal to an integral number of AC cycles. Sync ...
, which turns the clock's hands through a reduction
gear train A gear train is a mechanical system formed by mounting gears on a frame so the teeth of the gears engage. Gear teeth are designed to ensure the pitch circles of engaging gears roll on each other without slipping, providing a smooth transmission ...
. The motor contains
electromagnet An electromagnet is a type of magnet in which the magnetic field is produced by an electric current. Electromagnets usually consist of wire wound into a coil. A current through the wire creates a magnetic field which is concentrated in the ...
s which create a rotating
magnetic field A magnetic field is a vector field that describes the magnetic influence on moving electric charges, electric currents, and magnetic materials. A moving charge in a magnetic field experiences a force perpendicular to its own velocity and to ...
which turns an iron
rotor Rotor may refer to: Science and technology Engineering *Rotor (electric), the non-stationary part of an alternator or electric motor, operating with a stationary element so called the stator * Helicopter rotor, the rotary wing(s) of a rotorcraft ...
. The rotation rate of the motor shaft is synchronized to the
utility frequency The utility frequency, (power) line frequency (American English) or mains frequency (British English) is the nominal frequency of the oscillations of alternating current (AC) in a wide area synchronous grid transmitted from a power station to th ...
; 60 cycles per second (Hz) in North America and parts of South America, 50 cycles per second in most other countries. The gear train scales this rotation so the minute hand rotates once per hour. Thus the synchronous clock can be regarded as not so much a timekeeper as a mechanical counter, whose hands display a running count of the number of cycles of alternating current. One of the gears turning the clock's hands has a shaft with a sliding friction fitting, so the clock's hands can be turned manually by a knob on the back or on the bottom, to set the clock. Synchronous motor clocks are rugged because they do not have a delicate pendulum or balance wheel. However, a temporary
power outage A power outage (also called a powercut, a power out, a power failure, a power blackout, a power loss, or a blackout) is the loss of the electrical power network supply to an end user. There are many causes of power failures in an electricit ...
will stop the clock, which will show the wrong time when power is restored. Some synchronous clocks (e.g.
Telechron Telechron is the name of a U.S. company that manufactured electric clocks between 1912 and 1992. "Telechron" is derived from the Greek word''tele'' meaning "far off," an''chronos'' "time," thus referring to the transmission of time over long dista ...
) have an indicator which shows if it has stopped and restarted.


Number of poles

Some electric clocks have a simple two-pole synchronous motor which runs at one revolution per cycle of power, i.e., 3600 
RPM Revolutions per minute (abbreviated rpm, RPM, rev/min, r/min, or with the notation min−1) is a unit of rotational speed or rotational frequency for rotating machines. Standards ISO 80000-3:2019 defines a unit of rotation as the dimensionl ...
at 60 Hz and 3000 RPM at 50 Hz. However most electric clocks have rotors with more magnetic poles (teeth), consequently rotating at a smaller submultiple of line frequency. This allows the gear train which turns the hands to be built with fewer gears, saving money.


Accuracy

The accuracy of synchronous clocks depends on how close
electric utilities An electric utility is a company in the electric power industry (often a public utility) that engages in electricity generation and distribution of electricity for sale generally in a regulated market. The electrical utility industry is a major p ...
keep the
frequency Frequency is the number of occurrences of a repeating event per unit of time. It is also occasionally referred to as ''temporal frequency'' for clarity, and is distinct from ''angular frequency''. Frequency is measured in hertz (Hz) which is eq ...
of their current to the nominal value of 50 or 60 hertz. Although utility load variations cause frequency fluctuations which may result in errors of a few seconds during the course of a day, utilities periodically adjust the frequency of their current using UTC atomic clock time so that the total number of cycles in a day gives an average frequency that is exactly the nominal value, so synchronous clocks do not accumulate error.NIST Paper
/ref> For example, European utilities control the frequency of their grid once a day to make the total number of cycles in 24 hours correct. U.S. utilities correct their frequency once the cumulative error has reached 3–10 sec. This correction is known as the Time Error Correction (TEC). In 2011, the
North American Electric Reliability Corporation The North American Electric Reliability Corporation (NERC) is a nonprofit corporation based in Atlanta, Georgia, and formed on March 28, 2006, as the successor to the North American Electric Reliability Council (also known as NERC). The original N ...
(NERC), a consensus-based industry organization, petitioned the
Federal Energy Regulatory Commission The Federal Energy Regulatory Commission (FERC) is the United States federal agency that regulates the transmission and wholesale sale of electricity and natural gas in interstate commerce and regulates the transportation of oil by pipeline in ...
(FERC) to eliminate the TEC. While this would have freed the power companies from the threat of fines and also provided an extremely modest increase in frequency stability, it was also noted that synchronous clocks, which include wall clocks, alarm clocks, and other clocks computing the time on the basis of their electrical power, would accumulate several minutes of error between the semi-annual resets for
Daylight Saving Time Daylight saving time (DST), also referred to as daylight savings time or simply daylight time (United States, Canada, and Australia), and summer time (United Kingdom, European Union, and others), is the practice of advancing clocks (typicall ...
. This consequence was reported in the American news media, and the initiative was dropped. However, in late 2016 a similar proposal was again filed by the NERC to the FERC, which was approved two months later. It is contingent upon the removal of the standard WEQ-006, and the NERC also petitioned the North American Energy Standard Board (NAESB), a non-governmental organization that is business-oriented, for removing that standard. If the FERC adopts the NAESB petition, TECs will no longer be utilized in the United States and Canada, and clocks timed by them will likely wander uncontrolled until manually reset, however as of 2021 WEQ-006 was still in place. It was noted in a technical paper by employees of the
National Institute of Standards and Technology The National Institute of Standards and Technology (NIST) is an agency of the United States Department of Commerce whose mission is to promote American innovation and industrial competitiveness. NIST's activities are organized into physical sci ...
and the
U.S. Naval Observatory United States Naval Observatory (USNO) is a scientific and military facility that produces geopositioning, navigation and timekeeping data for the United States Navy and the United States Department of Defense. Established in 1830 as the Depo ...
that, had TECs not been inserted in 2016, there would have been over seven minutes lost by electrically timed clocks over much of the United States and Canada, as shown in Figure 8 of their paper.


Spin-start clocks

The earliest synchronous clocks from the 1930s were not self-starting, and had to be started by spinning a starter knob on the back. A flaw in the design of these ''spin-start'' clocks was that the motor could be started in either direction, so if the starter knob was spun the wrong way the clock would run backwards, the hands turning counterclockwise. Later manual-start clocks had ratchets or other linkages which prevented backwards starting. The invention of the
shaded-pole motor The shaded-pole motor is the original type of AC single-phase induction motor, dating back to at least as early as 1890. A shaded-pole motor is a small squirrel-cage motor in which the auxiliary winding is composed of a copper ring or bar sur ...
allowed self-starting clocks to be made, but since the clock would restart after a power interruption, the loss of time would not be indicated.


See also

*
Master clock Master or masters may refer to: Ranks or titles * Ascended master, a term used in the Theosophical religious tradition to refer to spiritually enlightened beings who in past incarnations were ordinary humans *Grandmaster (chess), National Master ...
* Shortt-Synchronome clock *
Automatic watch An automatic watch, also known as a self-winding watch or simply an automatic, is a mechanical watch where the natural motion of the wearer provides energy to wind the mainspring, making manual winding unnecessary if worn enough. It is distinguis ...


Notes


References

*Viradez, Michel. History of Electric Clocks *Katz, Eugenii. Alexander Bain Biography *Perpetual Electromotive of Giuseppe Zamboni *Chirkin, K. Electromechanical clocks. ''Radio,'' 7 (1968): p. 43. {{Time topics Clock designs Scottish inventions 19th-century inventions