National Physical Laboratory

Time Scales Time Scales

NPL maintains the national time scale and contributes to international time, provides accurate time and frequency to users across the UK, and researches improved time scales and time transfer methods. 

Timekeeping today is based on highly stable atomic clocks that are able to run continuously over many years.

NPL operates a group of atomic clocks of two complementary types - active hydrogen masers and caesium clocks - that provide the national time scale UTC(NPL) and contribute to the generation of the world time system, Coordinated Universal Time (UTC).

The Time and Frequency group has considerable expertise in analysing clock and time transfer measurements. The noise processes present in local or remote clock difference measurements are investigated and modelled using Kalman filter-based techniques. These methods form the basis of time scale algorithms to compute time scales that are more stable than any of the contributing clocks. The techniques developed at NPL have applications in global navigation satellite system (GNSS) time scales, and our research into novel methods for space clocks analysis will help to enhance the performance of GNSS systems.

The NPL time scale is integrated into the international timing system by time transfer links that continuously measure the time differences between UTC(NPL) and other national time scales to high accuracy. Two complementary methods are used routinely, one based on the measurement of timing signals from navigation satellites and the other on exchanging time signals via a communications satellite. We are also researching new techniques such as time and frequency transfer over optical fibre.

As the UK’s centre of precise time and frequency measurement, NPL offers a range of services that provide access to a reliable and trusted source of time: the Time from NPL.