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transcript
Time and Time Time and Time TransferTransfer
Hugo Fruehaufhxf@fei-zyfer.com
Jan 2008
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•• What is TimeWhat is Time•• The Time StandardThe Time Standard
•• Time SourcesTime Sources
•• GPS Time TransferGPS Time Transfer
•• Time DilationTime Dilation
AgendaAgenda
3
What is Time?What is Time?““What then is time? If someone asks What then is time? If someone asks me, I know; If I wish to explain it to me, I know; If I wish to explain it to
someone who asks, I know notsomeone who asks, I know not””..
Bishop of HippoBishop of HippoNorth Africa 5th Century A.D.North Africa 5th Century A.D.
““Time is what a clock readsTime is what a clock reads””Albert EinsteinAlbert Einstein
““The clock, not the steam engine is the The clock, not the steam engine is the key machine of the industrial agekey machine of the industrial age””..
Lewis Mumford*Lewis Mumford*TechnicsTechnics & Civilization& Civilization
* U.S. Social critic and teacher, Stanford; U. of Pennsylvania; MIT; Wesleyan U.; (born 1895)
““Time is Money and Money is TimeTime is Money and Money is Time””(modified sayings of Benjamin Franklin and (modified sayings of Benjamin Franklin and George (Robert) GissingGeorge (Robert) Gissing…… my contribution)my contribution)
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•• PhilosophicallyPhilosophically
Time is relative to Quality of Life (H.F.)
•• Theoretically/MathematicallyTheoretically/Mathematically
Time is relative to Position (Albert Einstein)
Time and Our UniverseTime and Our Universe
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•• Universal Time (UT)Universal Time (UT)
Universal Time (UT) is the general designation of time scales based on the rotation of the earth. (GMT may be regarded as the general equivalent of UT)
In applications where imprecision of a few hundredths of a second cannot be tolerated, it is necessary to specify the form of UT:
– UT0 is the mean solar time of the prime meridian obtained fromdirect astronomical observation
– UT1 is UT0 corrected for the effects of small movements of theearth relative to the axis of rotation (polar variation)
– UT2 is UT1 corrected for the effects of a small seasonal fluctuation in the rate of rotation of the earth
(1) Taken in part from letter by, David Allan, NIST, to CCIR Study Group XII U.S. Committee Members. 3-17-89.
Definition of Terms for TimeDefinition of Terms for Time(1)
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•• International Atomic Time (International Atomic Time (TAITAI))
The time scale established by the Bureau International de Poids de Mesure' (BIPM) on the basis of data from atomic clocks operating in several establishments conforming to the definition of the second, the International System of Units (SI)
•• Universal Coordinated Time (Universal Coordinated Time (UTCUTC))
The time scale maintained by the BIPM which forms the basis of acoordinated dissemination of standard frequencies and time signals. It corresponds exactly in rate with TAI, but differs from it by an integral number of seconds
The UTC scale is adjusted by the insertion or deletion of seconds (positive or negative “leap seconds”) to ensure agreement with UT1 to within 0.9 seconds
Definition of Terms for TimeDefinition of Terms for Time(1)(cont)(cont)
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•• What is a leap second?What is a leap second?A leap second is a second added to Universal Coordinated Time (UTC) to make it agree with astronomical time to within 0.9 second. UTC is an atomic time scale, based on the performance ofatomic clocks. Astronomical time is based on the rate of rotation of the earth. Since atomic clocks are more stable than the rate at which the earth rotates, leap seconds are needed to keep the twotime scales in agreement.
The first leap second was added on June 30, 1972, and they occurat a rate of slightly less than one per year, on average. Although it is possible to have a negative leap second (a second removed from UTC), so far, all leap seconds have been positive (seconds added to UTC because of the slowing of the celestial system.
(2) Taken from the NIST Website http://www.nist.gov/
Definition of Terms for TimeDefinition of Terms for Time(2)(cont)(cont)
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•• What is a leap year?What is a leap year?Leap years are years with 366 days, instead of the usual 365. Leap years are necessary because the actual length of a year is 365.242 days, not 365 days, as commonly stated. Basically, leap years occur every 4 years, and years that are evenly divisible by 4 (2004, for example) have 366 days. This extra day is added to the calendar on February 29th
However, there is one exception to the leap year rule involving century years, like the year 1900. Since the year is slightly less than 365.25 days long, adding an extra day every 4 years results in about 3 extra days being added over a period of 400 years. For this reason, only 1 out of every 4 century years is considered as a leap year. Century years are only considered as leap years if they are evenly divisible by 400. Therefore, 1700, 1800, 1900 were not leap years, nor will year 2100. But 1600 and 2000 were leap years, because those year numbers are evenly divisible by 400
Definition of Terms for TimeDefinition of Terms for Time(2)(cont)(cont)
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Julian Day NumberJulian Day Number
A number of a specific day from a continuous day count having aninitial origin of 12 hours UT on 1 January 4713 BCE, the Julian Day zero of the Julian Calendar
Julian Date (JD)Julian Date (JD)
The Julian Day Number followed by the fraction of the day elapsed since the preceding noon (12 hours UT).For example: The day extending from 1900 January 0.5 d UT to 1900 January 1.5 d UT has the number 2,415,020.
Modified Julian Day (MJD)Modified Julian Day (MJD)
Equal to the Julian date shifted so its origin occurs at midnight on November 17, 1858. It differs from the Julian Day by 2,400,000.5 days. For example: The day extending from November 17, 1858 to May 18, 2004 has the MJD number 53,108.
Definition of Terms for TimeDefinition of Terms for Time(1)(cont)(cont)
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•• Julian calendarJulian calendarThe solar calendar introduced by Julius Caesar in Rome in 46 B.C., having a year of 12 months and 365 days and a leap year of 366 days every fourth year. It was eventually replaced by the Gregorian calendar.
•• Gregorian calendarGregorian calendarThe solar calendar in use throughout most of the world, sponsored by Pope Gregory XIII in 1582 as a corrected version of the Julian calendar.
Definition of CalendarsDefinition of Calendars
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•• What is TimeWhat is Time
•• The Time StandardThe Time Standard•• Time SourcesTime Sources
•• GPS Time TransferGPS Time Transfer
•• Time DilationTime Dilation
AgendaAgenda
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Definition of the Definition of the ‘‘SECONDSECOND’’
• The ‘SECOND’ is the duration of 9,192,631,770
periods of the radiation corresponding to the
transition between the two (unperturbed)
hyperfine levels of the ground state of the 133Cesium atom
• Established in 1967
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AT&T Phone Monopoly
(Model 625 Qz Osc for timing
Westinghouse)
’50s to ’70s1st Miniature Rb
Vapor Atomic Osc. (Efratom,
Munich)
1969Definition of the
“Second” per 133Cesium atom
(13th Conf. of Wtsand Measures)
1967
Timation Nav Sat (Qz)Transit Nav Sat (Qz)Loran Grd Nav (Cs)
Omega Grd Nav (Cs)WWVB Timing (Cs)
(FEI, HP)
’70s1st (4) GPS Block-I Sats Launched for Nav &
Timing (Rockwell)
Feb 1978
1st GPS Timing RCVR “TANS”
(Trimble)
1981
1st Rb built for Space, for
GPS Block-I Satellites
(Efratom-CA & Rockwell)
1975
1st GPS/Rb/Qz PRS Intro to
Wireless AT&T-Lucent
(Ball-Efratom)
19881st Mil Rb Intro to Mil/Gov (Ball-
Efratom)1983
1985-19891st USA
Com’l Passive Hydrogen
Maser (NIST & Ball-Efratom)
A host of GPS and Qz Companies;
also (4) Rb, (3) Cs, (3) Act Hm, and
(1) Pass Hm Companies
Late ’80s Early ’90s
GPS, Loran, Hm, Cs, Rb, and Qz everywhere in Infrastructure, Telecom, Gov,
Labs, etc.)
1st Com’l Rb Vapor Osc 19”
Rack (HP, GenRad, &
Tracor)
19591964Hi-Perf Qz Osc, Grd & Space (FEI)
World UTC
Defined
(FEI) enters Grd & Space Miniature Rb Market, buys Litton assets
1984
1st Rb Intro to Wired & Wireless
Telecom Nets (Ball-Efratom)
1985
1st GPS-aided Rb-PRS at
AT&T (AT&T & Ball-
Efratom)
1987(FTS & Kernco) enter Grd & Space
Cs Market1979
1st GPS/Rb Discipline
Module (Ball-Efratom)
1982
(EG&G) enters
Miniature Rb Mrkt
----
1st US Active Hydrogen Maser
(John Hopkins & Sigma-Tau)
(FEI &EG&G) enter Mil Rb Mrkt
1986
Active and Passive Hydrogen Masers (KVARZ, Russia)
Late ’60s
(FEI) enters Grd Cs Market
Intro of BITS Clocks to Wireline Telcos (Telecom
Solutions)
Early ’90sNew Mil SAASM GPS Timing Rcvr
(ATK)
1999WAAS GPS-
Augmentation System for the FAA Com’l
Aviation Navigation Infrastructure
2002
Wired and Wireless Telcos,Computer networks,Civil Infrastructure,
Gov/Mil Com, Cmd/Ctrl, and
Space Systems, all using PT&F Components and
Systems
Internet Timing Protocols, NTP, etc.
Mid ’90s
EU Galileo Test Sats Launches (Europe’s GPS
System)
2006
1st Com’l Cs Atomic Beam
Primary Std (HP)
1958
Qz Osc’s for Radars, Radios, & Transmitters
’40s
Precision Time Precision Time & Frequency & Frequency
HistoryHistory
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Atomic Energy LevelsAtomic Energy LevelsElectron Energy Levels - Electrostatic interaction between Proton and Electron (+ and - charges)
Fine Structure - Interaction between electron spin dipole moment and the magnetic field due to the electron’s orbital motion. ~1/50 of the first energy level.
Collapsing the orbit releases
energy
Expanding orbit requires energy
(Energy out or in is generally in the infrared-visible-UV frequencies)
(Energy out or in is generally in the microwave frequency area)
Hyperfine Structure - Magnetic dipole interaction between the electron spin dipole moment with the nucleus. ~1/1000 of fine structure interaction.
(Energy out or in is generally in the microwave frequencies and below)
f ≈ 1.4 GHz for Hydrogenf ≈ 6.8 GHz for Rubidiumf ≈ 9.2 GHz for Cesium
Zeeman Effect - Magnetic interaction between external magnetic field and electron and proton spin dipoles.
(Energy out or in is generally in the audio frequency area and above)
N
SN
S
(Courtesy: Ed Mattison, Smithsonian from his tutorial 12-92 (a modification of his chart)
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9.2
0Ener
gy (F
requ
ency
) (G
Hz)
Magnetic Field HO Energy statesat H = HO
(F, mF)(4,4)(4,3)(4,2)(4,1)(4,0)(4,-1)(4,-2)(4,-3)(4,-4)
(3,-3)(3,-2)(3,-1)(3,0)(3,1)(3,2)(3,3)
9.192,631,770 GHz
Cesium Hyperfine Energy LevelsCesium Hyperfine Energy Levels
Courtesy of John Vig, U.S. Army Communications-Electronics Command, Fort Monmouth, NJ
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Atomic state selection Cs atom detection
ATOMIC BEAMSOURCE
ATOMIC BEAM
Cs VAPOR, CONTAINING AN EQUALAMOUNT OF THE TWOKINDS OF Cs ATOMS
VACUUM CHAMBER
MAGNET(STATE SELECTOR)
N
S
KIND 1 - ATOMS(LOWER STATE)
KIND 2 - ATOMS(UPPER STATE)
DETECTOR
DETECTOR
MAXIMUM SIGNAL
NO SIGNAL
S
S
N
N
MAGNET
MAGNET
MICROWAVECAVITY
MICROWAVECAVITY
MICROWAVE SIGNAL(OF ATOMIC RESONANCEFREQUENCY)
STATE SELECTEDATOMIC BEAM
STATE SELECTEDATOMIC BEAM
NO SIGNAL
6-10
Cesium Beam Atomic Frequency StandardCesium Beam Atomic Frequency Standard
Courtesy of John Vig, U.S. Army Communications-Electronics Command, Fort Monmouth, NJ
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Output
State Selection Magnets (7)
(2)
Cesium Source (1)
(5) (6)Beam Tube (3)
Cesium Beam Atomic Frequency StandardCesium Beam Atomic Frequency Standard
Cesium Oven (4)
(1) Active Element of Choice(2) Controlled Environment(3) Element Container(4) Atomic Pump(5) Resonator(6) Irradiation Source(7) State Detector(s)(8) Control Electronics(9) Frequency Source(10) Ion Pump and Getters
Hot Wire Ionizer (7)
5 MHz
~9.2 GHz
DC+Mod Freq
Qz Osc (9)
Servo (8)
Synth(8a)
(10)
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•• What is TimeWhat is Time
•• The Time StandardThe Time Standard
•• Time SourcesTime Sources•• GPS Time TransferGPS Time Transfer
•• Time DilationTime Dilation
AgendaAgenda
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Relative vs. Systems Time SyncRelative vs. Systems Time Sync
Systems time usually refers Systems time usually refers to a Time Sync of the user to a Time Sync of the user
group obtained from an group obtained from an external source.external source.
One User can be selected at random to be the master
for the group
In general, relative time In general, relative time refers to a Time Sync within refers to a Time Sync within
the group of users.the group of users.
Relative Time
UserUser
User
User
User
User
User
(A System)
MC
A Master Station within the system
might be the reference for all
or
Systems TimeSystems Time
User
User
User
User
User
(A System)
User
UTC or
Other
User
UTC or another external world standard is the master for the group
Timing Capabilities From Various SystemsTiming Capabilities From Various Systems
100 (S)
10-3 (MilliS)
10-6 (MicroS)
10-9 (NanoS)
1,500,000 ns3,000,000 ns
1,000,000 ns
30,000 ns
5,000 nsCommunication Network Requirement
1,000 ns500 ns
<10 ns
Sync
h ro n
izat
ion
Acc
u ra c
y
Local Coverage Only
Global Coverage
Fort Collins Radio
GOES Sat
(UTC)
Radio Phone (UTC)
WWVB Radio (UTC)
Transit Nav. Sat.
Omega Portable Clock Trips
GPS (UTC)
(UTC) Traceable to Universal Coordinated Time
Navigation Requirement Long and Short Range
Shut
DownShut
Down
No
Longer
Practical
Common View
(DGPS) WAAS
EGNOS MSAS
GAGAN
<10 ns
~500 ns
eLoran (UTC)
10-7
10-8
<100 nsGlobal
Close to
being
shut
down
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•• What is TimeWhat is Time
•• The Time StandardThe Time Standard
•• Time SourcesTime Sources
•• GPS Time TransferGPS Time Transfer•• Time DilationTime Dilation
AgendaAgenda
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UTC UTC ““CommonCommon--ViewView”” Time Transfer via GPSTime Transfer via GPS
- BIPM (International Time Bureau)- TAI (International Atomic Time)
*UTC is maintained within 0.9 sec. of UT-1. If exceeded, UTC is
corrected + one second (“Leap-Second”)
Russia
Germany
EnglandBIPM BIPM ParisParis
TAI TAI Time Time (PaperScale)
Atomic Clocks and Time Scales UTC* UTC*
Time Scale
Etc.
China
UTUT--11Time Time (Earth
Rotation)
Common ViewTime Transfer
GPS Satellites
Com
mon
Vie
wTi
me
Tran
sfer
Others
USNOUSNO
GPS Master GPS Master Control Station Control Station
(MCS)(MCS)
Data Exchange
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GPS Time Keeping InfrastructureGPS Time Keeping Infrastructure
GPS Satellites
USNO Wash. DC
NRL
GPS TimeGPS Time≤100 ns of UTC (USNO-Master Clock)
Monitor Monitor StationStation
Cs Clocks (Diego Garcia)
Satellite Control Uplink
Monitor Monitor StationStation
Cs Clocks (Hawaii)
Monitor Monitor Station Station
Cs Clocks (Ascension)
Monitor Monitor StationStation
Cs Clocks (Kwajalein)
Satellite L-Band Downlink
GPS Satellites
GPS Master GPS Master Control StationControl Station
(MCS-Schriever AFB)
Monitor Monitor Station Station
Cs Clocks (Schriever)
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Separating Sat. Clock and Sat. Position ErrorSeparating Sat. Clock and Sat. Position Error
GPS Satellites
Monitor Monitor StationStation
Cs Clocks (Diego Garcia)
Monitor Monitor StationStation
Cs Clocks (Hawaii)
Monitor Monitor Station Station
Cs Clocks (Ascension)
Monitor Monitor StationStation
Cs Clocks (Kwajalein)
GPS Satellites
Monitor Monitor Station Station
Cs Clocks (Schriever)
Ephemeris
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UTC is related to PositionUTC is related to Position
Assume User #1 and User #2 are receiving the same satellite signal.
Both receive time but it will not be to <100 Nanoseconds of UTC.
GPS Satellite If signal has to travel 1000
miles further to reach User #2, then propagation delay of about 5.3 ms must be calibrated out.
User must first resolve his position before <100 Nanosec off UTC (USNO-MC) is possible.
∆ Miles
User #2
User #1
1
4
3
2
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•• What is TimeWhat is Time
•• The Time StandardThe Time Standard
•• Time SourcesTime Sources
•• GPS Time TransferGPS Time Transfer
•• Time DilationTime Dilation
AgendaAgenda
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Developed by Albert Einstein in 1905. He used a “Thought Experiment”in which he rode through space on a beam of light.
Stationary observer not on the train ∆tR = (1.6911886) (10 sec) = 16.911 sec
EinsteinEinstein’’s Special Theory Of Relativitys Special Theory Of Relativity
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2R
CV1
tt
⎥⎥⎦
⎤
⎢⎢⎣
⎡⎟⎠⎞
⎜⎝⎛−
∆=∆
Train travels
150,000Mi/Sec
Clock
Flashlight
Path oflight pulse
Mirror
10 SECONDS PASS; 5 pulses down and back up10 SECONDS PASS; 5 pulses down and back up
Observerin the train
Path ofLight Pulse
Train travels
150,000Mi/Sec
16.911 SECONDS PASS; 5 pulses down and back up16.911 SECONDS PASS; 5 pulses down and back up
One of (2) main effects (Special and General Theory of Relativity)
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Clock Relativity ConsiderationsClock Relativity Considerations
2000 4000 6000 8000 10,000 12,000Altitude (nmi)
-6
GPS = 10,898 nmi
Circular Orbits
14,000
6
2
Rel
ativ
istic
Effe
ct, ∆
f/fx1
0-10
-2
-4
4
0
Special Theory of RelativitySpecial Theory of Relativity
112
12
−⎥⎥⎦
⎤
⎢⎢⎣
⎡⎟⎠⎞
⎜⎝⎛−=
∆CV
ff s
21
ss V
V ⎥⎦
⎤⎢⎣
⎡ µ=
1010x83.0ff −−=
∆ For GPS:
1010x3.5ff −=
∆For GPS:
General Theory of Relativity
⎥⎦
⎤⎢⎣
⎡−+=
∆
srer1
2Cer
egff
ZeroEffect
ZeroEffect
Total Relativistic Effect on GPS Clocks ∆f/f 4.47E-10
Total Relativistic Effect on GPS Clocks ∆f/f 4.47E-10
10
.sec
1046.4400,86 −∗=∆
∗=∆ xfftt
dayoner nsec621,38=∆ rt Original Clocks set to:
10,229,999.995433 Hz