Editing Clock (section)

==Operation==

The invention of the mechanical clock in the 13th century initiated a change in timekeeping methods from continuous processes, such as the motion of the [[gnomon]]'s shadow on a sundial or the flow of liquid in a water clock, to periodic oscillatory processes, such as the swing of a pendulum or the vibration of a [[crystal oscillator|quartz crystal]],<ref name="Cipolla" /><ref name="Marrison1">{{cite journal
 | last1  = Marrison
 | first1 = Warren A.
 | title = The Evolution of the Quartz Crystal Clock
 | journal = Bell System Tech. J.
 | volume = 27
 | issue = 3
 | pages = 511–515
 | date = July 1948
 | url = https://archive.org/details/bstj27-3-510
 | doi = 10.1002/j.1538-7305.1948.tb01343.x
 | access-date = February 25, 2017}}</ref> which had the potential for more accuracy. All modern clocks use oscillation.

Although the mechanisms they use vary, all oscillating clocks, mechanical, electric, and atomic, work similarly and can be divided into analogous parts.<ref name="Jespersen">{{cite book|last=Jespersen|first=James|author2=Fitz-Randolph, Jane|author3=Robb, John|title=From Sundials to Atomic Clocks: Understanding Time and Frequency|publisher=Courier Dover|year=1999|location=New York|url=https://books.google.com/books?id=Z7chuo4ebUAC&q=clock+resonance+pendulum&pg=PA42|isbn=978-0-486-40913-9|page=39|access-date=October 30, 2020|archive-date=July 3, 2023|archive-url=https://web.archive.org/web/20230703114213/https://books.google.com/books?id=Z7chuo4ebUAC&q=clock+resonance+pendulum&pg=PA42|url-status=live}}</ref><ref>{{cite web|title=How clocks work|work=InDepthInfo|publisher=W. J. Rayment|year=2007|url=http://www.indepthinfo.com/clocks/index.shtml|access-date=2008-06-04|archive-date=May 15, 2008|archive-url=https://web.archive.org/web/20080515221938/http://www.indepthinfo.com/clocks/index.shtml|url-status=live}}</ref><ref name="Milham">{{cite book|last=Milham|first=Willis I.|title=Time and Timekeepers|publisher=MacMillan|year=1945|location=New York|isbn=978-0-7808-0008-3|page=74}}</ref> They consist of an object that repeats the same motion over and over again, an ''[[oscillator]]'', with a precisely constant time interval between each repetition, or 'beat'. Attached to the oscillator is a ''controller'' device, which sustains the oscillator's motion by replacing the energy it loses to [[friction]], and converts its oscillations into a series of pulses. The pulses are then counted by some type of ''counter'', and the number of counts is converted into convenient units, usually seconds, minutes, hours, etc. Finally some kind of ''indicator'' displays the result in human readable form.

===Power source===

{{Flowlist|
* In mechanical clocks, the power source is typically either a weight suspended from a cord or chain wrapped around a [[pulley]], [[sprocket]] or drum; or a spiral spring called a [[mainspring]].  Mechanical clocks must be ''wound'' periodically, usually by turning a knob or key or by pulling on the free end of the chain, to store energy in the weight or spring to keep the clock running.
* In [[electric clock]]s, the power source is either a [[Battery (electricity)|battery]] or the [[Mains power|AC power line]]. In clocks that use AC power, a small backup battery is often included to keep the clock running if it is unplugged temporarily from the wall or during a power outage.  Battery-powered analog wall clocks are available that operate over 15 years between battery changes.
}}
{{clear}}

===Oscillator===

[[File:Floating Balance Escapement.gif|thumb|[[Balance wheel]], the oscillator in a mechanical [[mantel clock]]. ]]

The timekeeping element in every modern clock is a [[harmonic oscillator]], a physical object ([[resonator]]) that vibrates or oscillates repetitively at a precisely constant frequency.<ref name="Marrison" /><ref name="Mondschein">{{cite book
 | last1  = Mondschein
 | first1 = Kenneth
 | title  = On Time: A History of Western Timekeeping
 | publisher = Johns Hopkins University Press
 | date   = 2020
 | page  = 88
 | isbn   = 978-1-4214-3827-6
 }}</ref><ref name="Britannica">{{cite encyclopedia
  | title = Mechanics: Simple harmonic oscillations
  | encyclopedia = Encyclopedia Britannica online
  | date = 2020
  | url = https://www.britannica.com/science/mechanics/Simple-harmonic-oscillations
  | access-date = 4 January 2023}}</ref><ref name="Bloomfield">{{cite book
 |last1        = Bloomfield
 |first1       = Louis
 |title        = How Everything Works: Making Physics Out of the Ordinary
 |publisher    = Wiley
 |date         = 2007
 |page        = 296
 |url          = https://books.google.com/books?id=_ZNxDwAAQBAJ
 |isbn         = 978-0-470-17066-3
 |access-date  = March 19, 2023
 |archive-date = April 4, 2023
 |archive-url  = https://web.archive.org/web/20230404215125/https://books.google.com/books?id=_ZNxDwAAQBAJ
 |url-status   = live
}}</ref>
* In mechanical clocks, this is either a pendulum or a [[balance wheel]].
* In some early electronic clocks and watches such as the [[Accutron]], they use a [[tuning fork]].
* In [[quartz clock]]s and watches, it is a [[crystal oscillator|quartz crystal]].
* In [[atomic clock]]s, it is the vibration of electrons in atoms as they emit microwaves.
* In early mechanical clocks before 1657, it was a crude balance wheel or [[Verge escapement|foliot]] which was not a harmonic oscillator because it lacked a [[balance spring]]. As a result, they were very inaccurate, with errors of perhaps an hour a day.<ref>Milham, 1945, p. 85</ref>
The advantage of a harmonic oscillator over other forms of oscillator is that it employs [[resonance]] to vibrate at a precise natural [[resonant frequency]] or "beat" dependent only on its physical characteristics, and resists vibrating at other rates. The possible precision achievable by a harmonic oscillator is measured by a parameter called its [[Q factor|Q]],<ref>{{cite web|title=Quality factor, Q|work=Glossary|publisher=Time and Frequency Division, NIST (National Institute of Standards and Technology)|year=2008|url=http://tf.nist.gov/general/enc-q.htm|access-date=2008-06-04|archive-url=https://web.archive.org/web/20080504160852/http://tf.nist.gov/general/enc-q.htm|archive-date=May 4, 2008}}</ref><ref>{{cite book| url = https://books.google.com/books?id=Z7chuo4ebUAC&pg=PA44| title = Jespersen 1999, pp. 47–50| isbn = 978-0-486-40913-9| last1 = Jespersen| first1 = James| last2 = Fitz-Randolph| first2 = Jane| date = January 1999| publisher = Courier Corporation| access-date = November 6, 2015| archive-date = July 3, 2023| archive-url = https://web.archive.org/web/20230703114215/https://books.google.com/books?id=Z7chuo4ebUAC&pg=PA44| url-status = live}}</ref> or quality factor, which increases (other things being equal) with its resonant frequency.<ref>{{cite book|last=Riehle|first=Fritz|title=Frequency Standards: Basics and Applications|publisher=Wiley VCH Verlag & Co.|year=2004|location=Germany|page=9|url=https://books.google.com/books?id=WZ34pQV-DXMC&q=Q+linewidth+%22split+the+line%22&pg=PA9|isbn=978-3-527-40230-4|bibcode=2004fsba.book.....R}}{{Dead link|date=February 2024 |bot=InternetArchiveBot |fix-attempted=yes }}</ref> This is why there has been a long-term trend toward higher frequency oscillators in clocks. Balance wheels and pendulums always include a means of adjusting the rate of the timepiece. Quartz timepieces sometimes include a rate screw that adjusts a [[capacitor]] for that purpose. Atomic clocks are [[Standard (technical)|primary standards]], and their rate cannot be adjusted.

====Synchronized or slave clocks====

[[Image:Greenwich clock 1-manipulated.jpg|thumb|The [[Shepherd Gate Clock]] at the [[Royal Observatory, Greenwich]] receives its timing signal from within the [[Royal Observatory, Greenwich]].]]

Some clocks rely for their accuracy on an external oscillator; that is, they are automatically synchronized to a more accurate clock:
* [[Slave clock]]s, used in large institutions and schools from the 1860s to the 1970s, kept time with a pendulum, but were wired to a [[master clock]] in the building, and periodically received a signal to synchronize them with the master, often on the hour.<ref>Milham, 1945, pp. 325–328</ref> Later versions without pendulums were triggered by a pulse from the master clock and certain sequences used to force rapid synchronization following a power failure.
[[File:Telechron clock 2H07-Br Administrator.JPG|thumb|Synchronous electric clock, around 1940. By 1940 the synchronous clock became the most common type of clock in the U.S.]]
* Synchronous electric clocks do not have an internal oscillator, but count cycles of the 50 or 60 [[Hertz|Hz]] oscillation of the AC power line, which is synchronized by the utility to a precision oscillator. The counting may be done electronically, usually in clocks with digital displays, or, in analog clocks, the AC may drive a [[synchronous motor]] which rotates an exact fraction of a revolution for every cycle of the line voltage, and drives the gear train. Although changes in the grid line frequency due to load variations may cause the clock to temporarily gain or lose several seconds during the course of a day, the total number of cycles per 24 hours is maintained extremely accurately by the utility company, so that the clock keeps time accurately over long periods.
* Computer [[real-time clock]]s keep time with a quartz crystal, but can be periodically (usually weekly) synchronized over the [[Internet]] to atomic clocks ([[Coordinated Universal Time|UTC]]), using the [[Network Time Protocol]] (NTP).
* [[Radio clock]]s keep time with a quartz crystal, but are periodically synchronized to [[radio time signal|time signals]] transmitted from dedicated [[Radio clock#List of radio time signal stations|standard time radio stations]] or [[satellite navigation]] signals, which are set by atomic clocks.

===Controller===

This has the dual function of keeping the oscillator running by giving it 'pushes' to replace the energy lost to [[friction]], and converting its vibrations into a series of pulses that serve to measure the time.
* In mechanical clocks, this is the [[escapement]], which gives precise pushes to the swinging pendulum or balance wheel, and releases one gear tooth of the ''escape wheel'' at each swing, allowing all the clock's wheels to move forward a fixed amount with each swing.
* In electronic clocks this is an [[Electronic oscillator|electronic oscillator circuit]] that gives the vibrating quartz crystal or tuning fork tiny 'pushes', and generates a series of electrical pulses, one for each vibration of the crystal, which is called the [[clock signal]].
* In atomic clocks the controller is an evacuated microwave [[Cavity resonator|cavity]] attached to a microwave [[Electronic oscillator|oscillator]] controlled by a [[microprocessor]]. A thin gas of [[caesium]] atoms is released into the cavity where they are exposed to microwaves. A laser measures how many atoms have absorbed the microwaves, and an electronic feedback control system called a [[phase-locked loop]] tunes the microwave oscillator until it is at the frequency that causes the atoms to vibrate and absorb the microwaves. Then the microwave signal is divided by [[digital counter]]s to become the [[clock signal]].<ref>{{cite book| url = https://books.google.com/books?id=Z7chuo4ebUAC&pg=PA61| title = Jespersen 1999, pp. 52–62| isbn = 978-0-486-40913-9| last1 = Jespersen| first1 = James| last2 = Fitz-Randolph| first2 = Jane| date = January 1999| publisher = Courier Corporation| access-date = November 6, 2015| archive-date = July 3, 2023| archive-url = https://web.archive.org/web/20230703114216/https://books.google.com/books?id=Z7chuo4ebUAC&pg=PA61| url-status = live}}</ref>
In mechanical clocks, the low [[Q factor|Q]] of the balance wheel or pendulum oscillator made them very sensitive to the disturbing effect of the impulses of the escapement, so the escapement had a great effect on the accuracy of the clock, and many escapement designs were tried. The higher Q of resonators in electronic clocks makes them relatively insensitive to the disturbing effects of the drive power, so the driving oscillator circuit is a much less critical component.<ref name="Marrison" />

===Counter chain===

This counts the pulses and adds them up to get traditional time units of seconds, minutes, hours, etc. It usually has a provision for ''setting'' the clock by manually entering the correct time into the counter.
* In mechanical clocks this is done mechanically by a [[gear train]], known as the [[wheel train (horology)|wheel train]]. The gear train scales the rotation speed to give a shaft rotating once per hour to which the [[minute hand]] of the clock is attached, a shaft rotating once per 12 hours to which the [[hour hand]] of the clock is attached, and in some clocks a shaft rotating once per minute, to which the [[clock face|second hand]] is attached.  The gear train also has a second function; to transmit mechanical power from the power source to run the oscillator. There is a friction coupling called the 'cannon pinion' between the gears driving the hands and the rest of the clock, allowing the hands to be turned to set the time.<ref>Milham, 1945, p. 113</ref>
* In digital clocks a series of [[integrated circuit]] [[counter (digital)|counters]] or dividers add the pulses up [[Digital data|digitally]], using [[binary numeral system|binary]] logic. Often pushbuttons on the case allow the hour and minute counters to be incremented and decremented to set the time.

===Indicator===

[[File:Cuckoo strikes the 8th hour.ogv|thumb|right|A [[cuckoo clock]] with mechanical automaton and sound producer striking on the eighth hour on the analog dial]]

This displays the count of seconds, minutes, hours, etc. in a human readable form.
* The earliest mechanical clocks in the 13th century did not have a visual indicator and signalled the time audibly by striking bells. Many clocks to this day are [[striking clock]]s which strike the hour.
* Analog clocks display time with an analog [[clock face]], which consists of a dial with the numbers 1 through 12 or 24, the hours in the day, around the outside. The hours are indicated with an [[hour hand]], which makes one or two revolutions in a day, while the minutes are indicated by a [[Clock face|minute hand]], which makes one revolution per hour. In mechanical clocks a gear train drives the hands; in electronic clocks the circuit produces pulses every second which drive a [[stepper motor]] and gear train, which move the hands.
* [[Digital clock]]s display the time in periodically changing digits on a digital display. A common misconception is that a digital clock is more accurate than an analog wall clock, but the indicator type is separate and apart from the accuracy of the timing source.
* [[Talking clock]]s and the [[speaking clock]] services provided by telephone companies speak the time audibly, using either recorded or digitally [[Voice synthesis|synthesized voices]].