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156:) used such master clocks in their electromechanical telephone exchanges to generate the call timing pulses necessary to charge telephone subscribers for their calls, and to control sequences of events such as the forcible clearing of connections where the calling subscriber failed to hang up after the called subscriber had done so. The UK had four such manufacturers, all of whom made clocks to the same GPO specification and which used the
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In early networks the slave clocks had their own timekeeping mechanism and were just corrected by the signals from the master clock every hour, 6, 12, or 24 hours. In later networks the slave clocks were simply counters which used a stepper motor to advance the hands with each pulse from the master
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throughout the building. In addition to wall clocks, it also controls time stamps that are used to stamp documents with the time, and a turret clock used in a clock tower. The "program clock" is a timer that can be programmed with punched paper tape to ring bells or turn machines on and off at
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Between the late 1800s and the availability of
Internet time services, many large institutions that depended on accurate timekeeping such as schools, offices, railway networks, telephone exchanges, and factories used master/slave clock networks. These consisted of multiple
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GPO Master clock type 36 Mark 3, by Gent and Co., UK. This clock was made with a synchronising mechanism, responsive to an external signal relayed by land line from the GPO Chronopher at St.Martin's le grand, which in turn, received it from the
Greenwich
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clock, once per second or once per minute. Some types, such as the
Synchronome, had optional extra mechanisms to compare the time of the clock with a national time service that distributed time signals from
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punches, and paper tape programmers which ran factory machines. Thousands of such systems were installed in industrial countries and enabled the precise scheduling which industrial economies depended on.
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attached to the mechanism, transmitted to the controlled equipment through pairs of wires. The controlled devices could be wall clocks, tower clocks, factory sirens, school bells,
81:. Networks of electric clocks connected by wires to a precision master pendulum clock began to be used in institutions like factories, offices, and schools around 1900. Modern
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Master clock from synchronised school clock system, c. 1928. Electromechanical movement winds each minute, and impulses slave clocks each minute. Operates on 24 volts DC.
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impulse system; these were Gent and Co., of
Leicester, Magneta Ltd of Leatherhead in Surrey, Synchronome Ltd of Alperton, north-west London, and Gillett and Johnson.
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and other timing devices, connected through wires to a master clock which kept them synchronized by electrical signals. The master clock was usually a precision
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units in the background are HP 5071A caesium beam clocks. The black units in the foreground are Sigma-Tau MHM-2010 hydrogen maser standards.
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Diagram of electric time system used around 1910 to keep time in factories, schools, and other large institutions. The master clock
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Master clock (at left) driving several slave clocks in an enthusiast's garage. The third one from the left at the top is a
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by telegraph wire. An example is the GPO time service in
Britain which distributed signals from the
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are synchronised by radio signals or
Internet connections to a worldwide time system called
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A modern, atomic version of a master clock is the large clock ensemble found at the
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and a robust mechanism. It generated periodic timing signals by
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Precision clock that synchronizes other clocks in a network
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73:that provides timing signals to synchronise
300:All about electric master and slave clocks
46:The master atomic clock ensemble at the
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286:. Vol. XXII. pp. 328–341.
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278:Engler, Edmund A. (January 1883).
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305:Examples of Master Clock Systems
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260:from the original on 2010-03-10
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325:Telecommunications equipment
89:(UTC), which is governed by
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284:The Popular Science Monthly
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10:
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87:Coordinated Universal Time
152:The British Post Office (
280:"Time keeping in London"
222:Shortt–Synchronome clock
141:clocks in a country's
139:astronomical regulator
101:U.S. Naval Observatory
48:U.S. Naval Observatory
32:radio-controlled clock
147:Greenwich Observatory
96:in many countries.
183:preprogrammed times.
254:"USNO Master Clock"
126:electrical contacts
310:GPO clock systems
143:naval observatory
91:primary reference
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122:seconds pendulum
52:Washington, D.C.
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294:External links
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94:atomic clocks
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79:clock network
77:as part of a
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262:. Retrieved
196:Observatory.
180:slave clocks
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114:slave clocks
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83:radio clocks
75:slave clocks
67:master clock
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56:rack-mounted
158:Hipp Toggle
319:Categories
264:2009-10-07
238:References
232:Escapement
130:time card
258:Archived
216:See also
120:with a
107:History
330:Clocks
71:clock
154:GPO
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50:in
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245:^
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65:A
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