Docstoc

Accuracy in Timekeeping – Atomic clocks and Time Servers -

Document Sample
Accuracy in Timekeeping – Atomic clocks and Time Servers - Powered By Docstoc
					?The development of atomic clocks throughout the twentieth century has been
fundamental to many of the technologies we employ everyday. Without atomic clocks
many of the innovations of the twentieth century would simply not exist.

Satellite communication, global positioning, computer networks and even the Internet
would not be able to function in the way we are used to if it wasn't for atomic clocks
and their ultra-precision in timekeeping.

Atomic clocks are incredibly accurate chronometers not losing a second in millions of
years. In comparison digital clocks may lose a second every week and the most
intricately accurate mechanical clocks lose even more time.

The reason for an atomic clock's incredible precision is that it is based on an
oscillation of a single atom. An oscillation is merely a vibration at a particular energy
level in the case of most atomic clocks they are based on the resonance of the caesium
atom which oscillates at exactly 9,192,631,770 times every second.

Many technologies now rely on atomic clocks for their unbridled accuracy. The global
positing system is a prime example. GPS satellites all have onboard an atomic clock
and it is this timing information that is used to work out positioning. Because GPS
satellites communicate using radio waves and they travel at the speed of light
(180,000 miles a second in a vacuum), tiny inaccuracies in the time could make
positioning inaccurate by hundreds of miles.

Another application that requires the use of atomic clocks is in computer networks.
When computers talk to each other across the globe it is imperative that they all use
the same timing source. If they didn't, time sensitive transactions such as Internet
shopping, online reservations, the stock exchange and even sending an email would
be near to impossible. Emails would arrive before they were sent and the same item
on an Internet shopping site could be sold to more than one person.

For this reason a global timescale called UTC (Coordinated Universal Time) based on
the time told by atomic clocks has been developed. UTC is delivered to computer
networks via times servers. Most time servers utilise NTP (network time protocol) to
distribute and synchronize the networks.

NTP time servers can receive UTC time from a number of sources most commonly
the onboard atomic clocks of the GPS system can be used as a UTC source by a time
server connected to a GPS antenna.

Another method that is quite commonly used by NTP time servers is to utilise the
long wave radio transmission broadcast by several countries' national physics
laboratories. Whilst not available everywhere and quite susceptible to local
topography the broadcasts do provide a secure method of receiving timing source.
If neither of these methods is available then a UTC timing source can be received
from the Internet although accuracy and security are not guaranteed.


Richard N Williams is a technical author and specialist in atomic clocks,
telecommunications, NTP and network time synchronisation helping to develop
dedicated NTP clocks. Please visit us for more information about a network time
server or other ntp server solutions.

				
DOCUMENT INFO