Time Synchronisation

Accurate time using Atomic Clocks is available across the entire globe using the GPS Atomic Clock time signal transmitted from a constellation of satellites above the Earth and a NTP GPS server which provides the ability to synchronize the time on computers and other electrical equipment.

The GPS signal is operated by the US Airforce (51st Space Wing) and was originally intended solely for military use but after an airliner was accidentally shot down during the cold war it was released for civilian use too.

GPS is currently the world’s only Global and Navigational Satellite System although the Europe Galileo project is expected to be completed by 2012.

GPS is based on a constellation of between 24 and 32 Medium Earth Orbit satellites. These satellite all house an onboard atomic clock. Atomic clocks are the most accurate timekeeping devices keeping time to within a few hundred nanoseconds.

A GPS receiver calculates its position on Earth by timing the signals sent by the GPS satellites. Each satellite continually transmits the time as told by its atomic clock along with information about the location of the satellite that sent it. The receiver uses the arrival time of each message to measure the distance to each satellite. By using the distance from four or more satellites the GPS receiver can work out via triangulation exactly where it is in the world.

Dedicated NTP GPS server (Network Time Protocol) are tuned to receive the GPS time signals are available. These devices connect o a computer network like any other server only these receive the timing signal and distribute it to other machines on the network using NTP (Network Time Protocol).

Richard Hawkesford © 2009