Clock network
A clock network or clock system is a set of synchronized clocks designed to always show exactly the same time by communicating with each other. Clock networks usually consist of a central master clock kept in sync with an official time source, and one or more slave clocks which receive and display the time from the master.
Synchronization sources
The master clock in a clock network can receive accurate time in a number of ways: through the
Clock networks in critical applications often include a backup source to receive the time, or provisions to allow the master clock to maintain the time even if it loses access to its primary time source. For example, many master clocks can use the reliable frequency of the alternating current line they are connected to.
Slave clocks
Slave clocks come in many shapes and sizes. They can connect to the master clock through either a cable or a short-range wireless signal. In the 19th century Paris used a series of pneumatic tubes to transmit the signal.[1] Some slave clocks will run independently if they lose the master signal, often with a warning light lit. Others will freeze until the connection is restored.
Clock synchronization
Many master clocks include the capability to synchronize devices like computers to the master clock signal. Common features include the transmission of the time via
Applications
One of the driving factors in developing clock networks was the broadcast industry.
While television broadcasters were some of the first users of clock networks, the equipment is becoming increasingly useful in other industries. For example, the National Emergency Number Association issued directive NENA-04-002, offering standards in timekeeping for 911 dispatch centers throughout the United States. Other common clock network users include airports and schools.
History
One of the first clock networks was installed by Charles Shepherd for the
In the period before the universal availability of A.C. mains or
Clock strata
This section needs expansion. You can help by adding to it. (May 2016) |
[1] There is a hierarchy of clocks in a network, reflecting their quality. For example:
- NTP clock strata
- Synchronization in telecommunications#Components
See also
- Radio clock
- Master clock
- Slave clock
- Time clock
- Time signal
- Time standard
- clock distribution network
References
- ^ ISBN 0316853550.