Overview of the National Measurement System’s Time and Frequency Programme
Dale Henderson Projects to support the maintenance of UTC
“The Maintenance and Development of UTC(NPL)” The objectives of this project are to support the operation and development of the international civil time scale, Coordinated Universal Time (UTC),
in partnership with the BIPM and the national time standards laboratories from other countries around the world;
and to provide a reference time standard for the UK that is traceable to the international civil time scale, Coordinated Universal Time (UTC). Its main deliverable is UTC(NPL), a continuously operating national time scale that is traceable to UTC, with the uncertainty in the UTC-UTC(NPL) offsets published in the BIPM Circular T to be established with an uncertainty of ± 5 ns (1s) or better. UTC and TAI
UT-1 is based on siderial time as monitored by the IERS
TAI maintained by BIPM under the Metre Convention
TAI is an Atomic time, step interval 1 SI second on the Geoid
UTC is “owned” by ITU (recommendation TF 460) and has the rate of TAI but is stepped to follow UT-1 International time-keeping since 1972
40 time laboratories around the world with more than 200 atomic clocks keep world time
Laboratory time standards compared using satellite links
Global standards – International Atomic Time (TAI) and Coordinated Universal Time (UTC) – are computed by the BIPM each calendar month
System calibrated by ~8 primary frequency standards 150
100
50 USNO PTB 0 NPL 50800 51300 51800 IEN -50
UTC - UTC(k) [ns] -100
-150 MJD EAL UTC(k) weighted mean of ~ 200 atomic clocks
Primary frequency TAI standards EAL calibrated to agree with SI second
UT UTC Earth's Rotation TAI with leap seconds inserted to keep UTC within +/- 0.9 s of UT
BIPM Circular T UT1-TAI (s) UTC-TAI (s) 0 1960 1970 1980 1990 2000 -5
-10
-15
-20 TimeOffset (s) -25
-30
-35 YEAR Time by post
TAI and UTC are post-processed time- scales
Each laboratory maintains its own UTC(k) in real-time
BIPM Circular T gives results for UTC - UTC(k) each month
In practice, standard time is only available from one of the 40 national laboratories, with the BIPM providing confirmation at a later date ‘Atomic’ Clocks in the NPL time scale
The UTC(NPL) time scale
- 3 Active hydrogen masers (Datum/Sigma Tau)
- 3 caesium clocks (HP5071A)
- Algorithms development Accuracy Requirements
Time ToD 1 s Accuracy Transport Internet
1ms Test & Broadcasting Measurement 1µs Power Telecomms MSF Astronomy GPS 1ns Sat.Nav. Geodesy Metrology
1ps No. of UK Users 10 10 2 10 3 10 4 10 5 10 6 10 7 The Maintenance and Development of UTC(NPL) – plan
Construct an atomic timescale using an algorithm to combine NPL’s clock’s optimally
A real-time implementation in hardware Projects to support the maintenance of UTC
“Primary Frequency Standards” The objective of this project is to realise the SI second at the highest levels of accuracy
and to relate those measurements to International Atomic Time (TAI)
and to support developments across the National Measurement System to link the primary standards of time and length.
Its main deliverable is a primary frequency standard contributing to TAI in each year of the Programme. Research into Atomic Standards Fountain’s operation
laser beams
magnetic • pulsed operation, 1.5 s sequence; shielding • launch by moving molasses; • up to 1 m high (>30 cm above C-field (2) microwave cavity); solenoid •108 atoms in MOT; microwave to • launch temperature 2.5 mK (1.3 cavity pump cm/s); MOT 5 6 coils (1) •10 –10 atoms detected; • two-channel detection for caesium waveguide reservoir normalisation; transformer fluorescence • RF pulse selecting mF=0 atoms. detection (3) Fountain’s operation Primary frequency standards at NPL
1.0
0.8
0.6
0.4
transition probability 0.2
0.0 -80 -60 -40 -20 0 20 40 60 80 microwave frequency - 9192631770 [Hz]
0.9
0.8
0.7
s 0.6
0.5
arbitrary unit 0.4
0.3
0.2
0.1 -1.5 -1.0 -0.5 0.0 0.5 1.0 1.5 f - 9192631770 [Hz] Primary frequency standards at NPL
combined uncertainty of CsF1-HM1 = 1.6 x 10-15
CsF1-UTC = 1.9 x 10-15
December comparison with PTB: MJD 2995-3000
Feb -March "campaign“ MJD 53054-53084 Primary frequency standards at NPL - plan
Reduce combined uncertainty of CsF1 incrementally
Lattice cooling for F2 – better stability and accuracy Projects to support the maintenance of UTC
“International Coordination and Representation” International Coordination and Representation
Representaion of the UK on :
Consultative committee for Time and Frequency
EUROMET
International Telecommunications Union : WP7a T&F broadcast, leap seconds NMS Time Programme 2003-2006
Projects to support the maintenance of UTC T11 “The Maintenance and Development of UTC(NPL)” T14 “Primary Frequency Standards” T16 “International Coordination and Representation”
Projects to support the development of UTC T12 “Algorithms and Analysis” T13 “Development of GNSS Time Transfer” T15 “Secondary Representation of the SI Second”
Projects to support NMS services T21 “MSF Standard-Frequency and Time Broadcasts” T22 “Monitoring Off-Air Time and Frequency Signals” T23 “Computer Time Services” T31 “Knowledge Transfer”