Co-ordinated Universal Time

Transcription

APMP Technical Committee
for Time and Frequency
Co-ordinated Universal Time
APMP-MEDEA Workshop
Participating in UTC
Beijing, November 6–7 2014
Michael Wouters, NMIA
A brief history of Co-ordinated Universal Time
1955
Invention of the caesium atomic clock
1960
Informal co-ordination of radio time-broadcasts based on
atomic time scales by USNO, Royal Greenwich Observatory
and NPL
1961
Official beginning of UTC on 1st January. Rate of UTC is set
equal to the rate of UT so that steps need to be introduced
to maintain synchronization.
1967
Redefinition of the SI second in terms of the 9.192GHz Cs
transition. Adoption of the name ‘Co-ordinated Universal
Time’ by the IAU
1972
UTC is defined to be offset from TAI by an integer number of
seconds and to have a rate equal to TAI. Leap seconds are
introduced.
APMP-MEDEA Workshop on Participation in UTC
-
-
Co-ordinated Universal Time 2
UTC and international organisations
ITU
International
Telecommunications
Union
definition of UTC
IERS
BIPM
=
BIPM
+
atomic timescale
International Earth
Rotation and
Reference Systems
Service
leap seconds
ITU and the definition of UTC
Three sectors:
1. ITU-T Standardisation
2. ITU-D Development
3. ITU-R Radio-communication
193 nations, 700 organizations
5000 technical advisors
Study Group 7: Working Party 7A
“Dissemination, reception and
coordination of standard-frequency
and time-signal services, including
the application of satellite
techniques, on a worldwide basis.”
UTC is defined by Rec. ITU-R TF.460-6 Standard-frequency and time-signal emissions
From Annex 1:
“UTC is the time-scale maintained by the BIPM, with assistance from the IERS, which forms
the basis of a coordinated dissemination of standard frequencies and time signals. It
corresponds exactly in rate with TAI but differs from it by an integer number of seconds.
The UTC scale is adjusted by the insertion or deletion of seconds (positive or negative leap
seconds) to ensure approximate agreement with UT1.”
ITU-R Working Party 7A is currently considering the future definition
and use of UTC. In particular, it is considering the future of leap seconds
-
-
-
Digression: more about leap seconds
2008-12-31
2012-06-30 Leap second addition
23:59:57
23:59:58
23.59:59
23:59:60
00:00:00
Digression: leap second issues
Timekeeping on computers
Leap second addition
23:59:57
23:59:58
23.59:59
23:59:60
00:00:00
.. but this is not how computers keep
time. They simply count the number of
seconds since some reference epoch eg
Unix-like systems such as Linux and Apple
OSX count the number of seconds since
January 1st 1970.
So what happens during a leap second ?
The clock gets stepped back one second.
This means that events during the leap second have ambiguous
time stamps, creating real problems such as computer crashes.
IERS and leap seconds
INTERNATIONAL EARTH ROTATION AND REFERENCE SYSTEMS SERVICE (IERS)
SERVICE INTERNATIONAL DE LA ROTATION TERRESTRE ET DES SYSTEMES DE REFERENCE
International Earth Rotation
and Reference Systems Service
Issues IERS Bulletin C ,
notifying whether or not
there will be a leap second in
the next 6 months.
SERVICE DE LA ROTATION TERRESTRE
OBSERVATOIRE DE PARIS
61, Av. de l'Observatoire 75014 PARIS (France)
Tel. : 33 (0) 1 40 51 22 29
FAX : 33 (0) 1 40 51 22 91
Internet : [email protected]
Paris, 7 July 2014
Bulletin C 48
To authorities responsible
for the measurement and
distribution of time
INFORMATION ON UTC – TAI
NO leap second will be introduced at the end of December 2014. The difference
between Coordinated Universal Time UTC and the International Atomic Time TAI is :
from 2012 July 1, 0h UTC, until further notice : UTC-TAI = -35 s
Leap seconds can be introduced in UTC at the end of the months of December or June,
depending on the evolution of UT1-TAI. Bulletin C is mailed every six months, either to
announce a time step in UTC, or to confirm that there will be no time step at the next
possible date.
Subscribe to Bulletin C
http://maia.usno.navy.mil/docrequest.html
The SI, BIPM and CIPM
SI
Bureau Internationale des Poids et Mesures
International
Committee for
Weights and
Measures (CIPM)
Consultative
Committee for
Temperature
Consultative
Committee for
Mass
Consultative
Committee for
Time and
Frequency
BIPM Time Department
definition of
the second
TAI and UTC
The Consultative Committee on
Time and Frequency
• Approximately 30 members, including NMIs and international
organisations such as the IAU, URSI, ITU
• Criteria for membership are that: the applicant be a national
laboratory; be active in research; and contribute to UTC.
• Meets in Paris every 2 to 3 years
Working Groups
• WG on International Atomic Time
• WG on Algorithms
• WG on Primary and Secondary Frequency Standards
• WG on Global Navigation Satellite Systems
• WG on Two-Way Satellite Time and Frequency Transfer
• WG on Coordination of the Development of Advanced Time
and Frequency Transfer Techniques
• WG on the CIPM MRA
• WG on Strategic Planning
• CCL-CCTF Frequency Standards WG
CCTF-K001.UTC: the key comparison in T&F
Measurand
[UTC - UTC(k)] in ns
UTC(k) is the local representation of UTC maintained by the laboratory k
Transfer device(s)
Time transfer between participants is carried out using Global Positioning
System (GPS) and Two-Way Satellite Time and Frequency Transfer
(TWSTFT)
Process for joining CCTF-K001.UTC
1. Satisfy the eligibility requirements
2. Contact BIPM Time Department, giving details of clocks and timetransfer equipment
3. BIPM assigns a laboratory identifier and numeric codes for each
clock.
http://kcdb.bipm.org/appendixB/appbresults/CCTF-K001.UTC/Guidelines_CCTF-K001.UTC.pdf
–
-
Requirements for participating in UTC
Organizational
• The laboratory must be an NMI or be sponsored by their NMI
• The country must be a Member State of the Metre
Convention or an Associate Member
Technical
• At least one clock (Cs or H-maser)
is required
• Time-transfer equipment such as a
GNSS timing receiver or TWSTFT station
Overview: the BIPM and UTC
Bureau International des
Poids et Mesures, Paris
 Clocks are compared over
large distances (via GPS typically)
 Each NMI submits their clock data to
BIPM
TAI
 TAI/UTC is calculated as a weighted
average of contributing clocks
UTC
 BIPM Circular T reports the offsets
of contributing clocks with respect to
UTC
Circular
T
Calibration of delays in time links
antenna
amplifier
distribution
GNSS Rx
It’s hard to measure these delays
so usually the combined delay is
calibrated by comparison with a
calibrated receiver.
An uncalibrated receiver is given a nominal
uncertainty of 20 ns by BIPM.
At the international level, calibration of a small number of reference
receivers is performed by the BIPM.
At the RMO level, calibration of receiver delays is co-ordinated by the
eg APMP TCTF Working Group on GNSS.
Contact: [email protected]
-
Reporting data to BIPM
Clock data
Clock data file - measurements of
UTC(k) – clock at UTC0 on MJDs
xxxx4 and xxxx9
Time-transfer data
CGGTTS data (format defined by the CCTF)
and/or
RINEX data (format defined by the IGS)
can submit data from multiple receivers
All data are uploaded to the BIPM ftp server,
preferably each day, but required by 4th day
of the month.
Clock data files
MJD
lab code
TA code
clock code
UTC(lab)-clock
56904 10005 0020005 0002017.0 1400509 0060910.3 1400508 0075879.6 1400506 0089525.5
56904 10005 1400590 0043636.8 1920002 0030073.9 1920001 0032798.0 1351072 0011137.8
56904 10005 1350415 0058735.1 1350128 0061360.1
56909 10005 0020005 0002017.3 1400509 0060924.4 1400508 0076024.0 1400506 0089537.9
56909 10005 1400590 0043636.8 1920002 0030083.4 1920001 0032809.6 1351072 0011191.8
56909 10005 1350415 0058700.3 1350128 0061399.9
56914 10005 0020005
1400509
0060938.7
1400506
12 HEWLETT-PACKARD
5061A 0002017.3 21
OSCILLOQUARTZ
32101400508 0076174.3
50 FREQ.
AND 0089550.5
TIME SYSTEMS INC. 4065A
13 EBAUCHES,
OSCILLATOM
B5000
OSCILLOQUARTZ
OSA1920001
3230B
51 DATUM/SYMMETRICOM
56914 10005
1400590
0043637.1 22
1920002
0030093.3
0032823.5
1351072 0011252.3 4065 B
14 HEWLETT-PACKARD
5061A OPT.
4
23
OSCILLOQUARTZ
EUDICS 3020
52 DATUM/SYMMETRICOM 4065 C
56914 10005 1350415
0058666.7
1350128
0061432.1
16 OSCILLOQUARTZ 3200
OSCILLOQUARTZ OSA 3235B
53 DATUM/SYMMETRICOM 4310 B
56919 10005 0020005 0002016.6 24
1400509
0060952.6 1400508 0076321.7
1400506 0089564.3
17 OSCILLOQUARTZ
25 HEWLETT_PACKARD 5062C
56919 10005 1400590
0043636.8 30
1920002
0030101.45061B
1920001 0032834.0 1351072 0011309.9
Cs III
HEWLETT-PACKARD
56919 10005 1350415
0058637.3 31
1350128
0061462.75061B OPT. 4
Cs 4000
HEWLETT-PACKARD
56924AND
10005
0020005
1400509
0000007.7
1400508
19 RHODES
SCHWARZ
XSC 0002016.6 34
H-P 5061A/B
with 5071A
tube 0076472.6 1400506 0089579.7
4x HYDROGEN
MASERS
H-P/AGILENT/SYMMETRICOM
High perf.
56924 10005
1400590 0043637.4 35
1920002
0030106.5 19200015071A
0032845.5
1351072 0011370.5
9x PRIMARY
CLOCKS1350415
AND PROTOTYPES
H-P/AGILENT/SYMMETRICOM
5071A Low perf.
56924 10005
0058600.5 36
1350128
0061489.7
56929 10005 0020005 0002016.2 1400509 0000022.6 1400508 0076632.6 1400506 0089595.6
56929 10005 1400590 0043637.7 1920002 0030114.3 1920001 0032854.7 1351072 0011433.8
56929 10005 1350415 0058568.3 1350128 0061515.2
56922.54 1400509 -060959.5 00000.000 PTB 10005
last line indicates any phase and frequency steps
-
Reporting of clock steps
Reporting of known clock steps is important because they can affect UTC
clock step
time scale
with step
time
When steps are reported BIPM can:
1. Correctly weight the clock (otherwise it looks unstable)
2. Correct the data so that it is continuous and is reported in Circular T
without the step
The reported clock step is calculated as
NEW_VALUE – OLD_VALUE
Monthly UTC reporting at NMIA
A Work Instruction sets out all steps to be followed
in the submission process.
Clock records for the last 2 months are plotted and
examined for outliers, steps, …
The clock data file is generated and checked.
The data are then checked again by another person
before upload to BIPM.
Time-transfer files which are uploaded daily (RINEX,
CGGTTS) are checked.
The whole process takes about 1.5 hours
How UTC is calculated
clock and link data
400 clocks
70 laboratories
weighted
mean
EAL
Primary Frequency
Standard evaluations
9 reported in Sep 2014
Echelle Atomique Libre
Free Atomic Time
correction
TAI
IERS
leap seconds
Weights are based on the principle that
a good clock is predictable and are
derived from the difference between
the observed and predicted frequency
of a clock over the past 12 months
Temps Atomique International
International Atomic Time
UTC
Circular T
Aside: primary standards
The value of a primary standard is defined and its practical realization is then corrected
for known perturbations.
Type B uncertainties δf/f × 10-15
NIST-F1 caesium fountain
Physical effect
Magnitude
Uncertainty
Second-order Zeeman
180.60
0.013
Spin exchange
-0.41
0.15
Blackbody
-22.98
0.28
Gravitation
179.95
0.03
Cavity pulling
0.02
0.02
Rabi/Ramsey pulling
10-4
10-4
Microwave effects
0.026
0.12
Cavity phase
0.02
0.02
Light shift
10-5
10-5
Adjacent transition
0.02
0.02
Microwave spectrum
0.003
0.003
Integrator offset
0
0.01
AM on microwaves
0
10-4
AC Zeeman (heaters)
0.05
0.05
TOTAL
0.34
How UTC is reported: Circular T
CIRCULAR T 321
2014 OCTOBER 09, 13h UTC
ISSN 1143-1393
BUREAU INTERNATIONAL DES POIDS ET MESURES
ORGANISATION INTERGOUVERNEMENTALE DE LA CONVENTION DU METRE
PAVILLON DE BRETEUIL F-92312 SEVRES CEDEX TEL. +33 1 45 07 70 70 FAX. +33 1 45 34 20 21
[email protected]
1 - Coordinated Universal Time UTC and its local realizations UTC(k). Computed values of [UTC-UTC(k)]
and uncertainties valid for the period of this Circular.
From 2012 July 1, 0h UTC, TAI-UTC = 35 s.
Date 2014
0h UTC
MJD
Laboratory k
AUG 30
56899
SEP 4
56904
SEP 9
56909
AOS
APL
AUS
BEV
BIM
-9.3
2.1
-153.4
-5.8
1605.4
-6.9
2.7
-150.4
-5.3
1609.4
-3.1
1.1
-164.0
-3.7
1646.2
(Borowiec)
(Laurel)
(Sydney)
(Wien)
(Sofiya)
SEP 14
SEP 19
56914
56919
[UTC-UTC(k)]/ns
-3.6
0.6
-170.9
-3.4
1661.8
-2.1
1.9
-185.4
-5.6
1682.7
SEP 24
56924
SEP 29
56929
Uncertainty/ns Note
uA
uB
u
-1.3
2.6
-194.7
-5.5
1700.4
-0.2
2.7
-207.2
-2.7
1699.9
0.3
0.3
0.3
1.5
1.5
5.3
5.3
5.3
3.5
7.2
5.3
5.3
5.3
3.8
7.4
6 - Time links and their uncertainties
...
Link
AOS
APL
AUS
BEV
BIM
/PTB
/PTB
/PTB
/PTB
/PTB
Type
GPSPPP
GPSPPP
GPSPPP
GPS MC
GPS MC
uA/ns
0.3
0.3
0.3
1.5
1.5
uB/ns
Calibration Type
5.0
5.0
5.0
3.0
7.0
LC(GPS P3)
LC(GPS MC)
GPS EC/GPS EC
BC(TWSTFT)
GPS EC/GPS EC
Calibration Dates
2011
2012
2010 Oct/2004
2008
2007 Nov/2006
Jun
Sep
Aug
Jan
Sep
Other data available from BIPM
Clock weights
PPP data and plots
change in clock weighting
method after 2014-01-01
nb the reference timescale is IGS
time not UTC
-
UTCr – Rapid UTC
• Purpose is to allow contributing laboratories to better monitor their
local UTC(k) and to provide quicker feedback for steering of time
scales
• Daily values of UTCr – UTC(k) are published each week
within
± 2 ns
of UTC
Note: UTCr is not a Key Comparison
Using Circular T
CIRCULAR T 321
2014 OCTOBER 09, 13h UTC
ISSN 1143-1393
BUREAU INTERNATIONAL DES POIDS ET MESURES
ORGANISATION INTERGOUVERNEMENTALE DE LA CONVENTION DU METRE
PAVILLON DE BRETEUIL F-92312 SEVRES CEDEX TEL. +33 1 45 07 70 70 FAX. +33 1 45 34 20 21
[email protected]
1 - Coordinated Universal Time UTC and its local realizations UTC(k). Computed values of [UTC-UTC(k)]
and uncertainties valid for the period of this Circular.
From 2012 July 1, 0h UTC, TAI-UTC = 35 s.
Date 2014
0h UTC
MJD
Laboratory k
AUG 30
56899
SEP 4
56904
SEP 9
56909
AOS
APL
AUS
BEV
BIM
-9.3
2.1
-153.4
-5.8
1605.4
-6.9
2.7
-150.4
-5.3
1609.4
-3.1
1.1
-164.0
-3.7
1646.2
(Borowiec)
(Laurel)
(Sydney)
(Wien)
(Sofiya)
SEP 14
SEP 19
56914
56919
[UTC-UTC(k)]/ns
-3.6
0.6
-170.9
-3.4
1661.8
-2.1
1.9
-185.4
-5.6
1682.7
SEP 24
56924
SEP 29
56929
Uncertainty/ns Note
uA
uB
u
-1.3
2.6
-194.7
-5.5
1700.4
-0.2
2.7
-207.2
-2.7
1699.9
0.3
0.3
0.3
1.5
1.5
5.3
5.3
5.3
3.5
7.2
5.3
5.3
5.3
3.8
7.4
Suppose we want to estimate the frequency of UTC(k) and its uncertainty on Sep 12.
Mean fractional frequency offset:
Link uncertainty:
… and then to interpolate we need to consider eg the stability of UTC(k)
Another approach
Nearly all of the devices (rubidiums, crystal oscillators) we calibrate at
NMIA are much less stable than our UTC(k) so the correction to UTC is
insignificant.
We therefore do not correct to UTC and make a statement in the
calibration report like ...
The instrument’s oscillator was compared in phase with the
National Frequency Standard before and after adjustment. The
results of these measurements ...
Other resources
BIPM workshop on TAI Training (2012)
http://www.bipm.org/ws/AllowedDocuments.jsp?ws=TAI_TRAINING
Thank you!
?

Co-ordinated Universal Time

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