Time & Frequency Glossary

AFNOR

A timecode developed by Association Francaise de Normalisation.

Atomic clock 

A clock using the natural resonance frequency of atoms as a time counter source. Caesium is the most accurate (and very expensive); rubidium is next accurate and is less cost-prohibitive and so is more widely used in commercial applications.

Board- Level /
Bus-Level Timing

Refers to timing boards used with computers to provide accurate local time information. Various categories available including PC, PCI, VME/VXE

Caesium, cesium

Element used in highly accurate atomic clocks

COTS

Commercial Off-the-Shelf.

DCF, DCF-77

Low frequency terrestrial radio signal from Frankfurt, Germany

Disciplined
oscillator

An oscillator that has been ‘disciplined’ or pre-calibrated to a time signal, e.g GPS

Frequency
Standard

Stable oscillator frequency used for calibration or reference

GALILEO

European Satellite Navigation System. It is currently in the process of being developed by the European Space Agency, and is intended to be fully operational by 2008.

GLONASS

Global Satellite Navigation System launched by the Russian Federation in 1999.

GMT

Greenwich Mean Time, local legal time in Britain

GPS

Global Positioning System

HaveQuick

Type of timecode that enables synchronous frequency hopping. It matches a Word of the Day code with Time of the Day code and a net number code, which is the table of frequencies to be used for that transmission.

IRIG

Inter Range Instrumentation Group. Developers of a set of timecodes which are widely used.

LCD

Liquid Crystal Display; Liquid crystals are suspended in small amount of liquid and then sandwiched between two glass plates.  When an electrical current is passed though, the crystals align so that light cannot pass through them. 

LED

Light Emitting Diode; A display technology that uses a semiconductor diode that emits light when charged.

Master clock, masterclock

A clock used as a primary reference for other sub-master (slave) clocks

Microsecond An SI unit of time equal to one millionth (10 to the minus 6) of a second. Its symbol is µs and it is equal to 1000 nanoseconds
Millisecond One thousandth of a second.  It is abbreviated to ms.

MSF, MSF-60

Low frequency terrestrial radio signal from Anthorn, Cumbria, England, broadcasting the national time standard

Nanosecond

One billionth of a second (10-9). It is abbreviated to ns and is equal to 1000 picoseconds

NIST

National Institute of Standards and Technology, the National Measurement Institute in the United States

NPL

National Physical Laboratory – the UK’s national measurement laboratory

NTP

Network Time Protocol, a method of transmitting time data across a computer network in order to synchronise internal clocks to a common time source.

 

Oscillator

An electronic device which generates a recurring waveform (the resonance frequency). This frequency is a counter to measure time and so is used extensively in clocks as a frequency reference source. 

Picosecond

One trillionth of a second (10-12) adn is abbreviated to ps. One picosecond is equal to 1000 femtoseconds

PRC

Primary Reference Clock

SDH

Synchronous Digital Hierarchy – the standard for transmitting digital information over optical networks such as SONET.

SMPTE

Time code developed by the Society for Motion Picture and Television Engineers. Adds a unique number onto each frame on a videotape denoting hours, minutes, seconds & frames in order to assist logging and editing of film, video and audio recordings.

SNMP

Simple Network Management Protocol, the internet protocol for network management software systems

SONET

Synchronus Optical Network

 

Stratum 1 Timeserver

 Device with a direct connection (not via a network) to a Stratum 0 time reference source

TAI

International Atomic Time. Time standard based on the vibrations of caesium atom.

Time server

Device that distributes time over a computer network in order to synchronise all the internal computer clocks.

Timecode

Time information in a coded signal format which facilitates synchronisation of any combination of message output, e.g. pictures with sound.

USNO

United States Naval Observatory, home to the atomic clock which is the source of national time in America

UT1

Time as defined by the Earth’s rotation

UTC

Co-ordinated Universal Time. The time calculated as a weighted average of about 200 atomic clocks around the world.