Enhanced View of Time Service Specification
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WWVB: a Half Century of Delivering Accurate Frequency and Time by Radio
Volume 119 (2014) http://dx.doi.org/10.6028/jres.119.004 Journal of Research of the National Institute of Standards and Technology WWVB: A Half Century of Delivering Accurate Frequency and Time by Radio Michael A. Lombardi and Glenn K. Nelson National Institute of Standards and Technology, Boulder, CO 80305 [email protected] [email protected] In commemoration of its 50th anniversary of broadcasting from Fort Collins, Colorado, this paper provides a history of the National Institute of Standards and Technology (NIST) radio station WWVB. The narrative describes the evolution of the station, from its origins as a source of standard frequency, to its current role as the source of time-of-day synchronization for many millions of radio controlled clocks. Key words: broadcasting; frequency; radio; standards; time. Accepted: February 26, 2014 Published: March 12, 2014 http://dx.doi.org/10.6028/jres.119.004 1. Introduction NIST radio station WWVB, which today serves as the synchronization source for tens of millions of radio controlled clocks, began operation from its present location near Fort Collins, Colorado at 0 hours, 0 minutes Universal Time on July 5, 1963. Thus, the year 2013 marked the station’s 50th anniversary, a half century of delivering frequency and time signals referenced to the national standard to the United States public. One of the best known and most widely used measurement services provided by the U. S. government, WWVB has spanned and survived numerous technological eras. Based on technology that was already mature and well established when the station began broadcasting in 1963, WWVB later benefitted from the miniaturization of electronics and the advent of the microprocessor, which made low cost radio controlled clocks possible that would work indoors. -
Mike Zornek • March 2020
Working with Time Zones Inside a Phoenix App Mike Zornek • March 2020 Terminology Layers of Wall Time International Atomic Time (ITA) Layers of Wall Time Universal Coordinated Time (UTC) International Atomic Time (ITA) Layers of Wall Time Universal Coordinated Time (UTC) Leap Seconds International Atomic Time (ITA) Layers of Wall Time Standard Time Universal Coordinated Time (UTC) Leap Seconds International Atomic Time (ITA) Layers of Wall Time Standard Time Time Zone UTC Offset Universal Coordinated Time (UTC) Leap Seconds International Atomic Time (ITA) Layers of Wall Time Wall Time Standard Time Time Zone UTC Offset Universal Coordinated Time (UTC) Leap Seconds International Atomic Time (ITA) Layers of Wall Time Wall Time Standard Offset Standard Time Time Zone UTC Offset Universal Coordinated Time (UTC) Leap Seconds International Atomic Time (ITA) Things Change Wall Time Standard Offset Politics Standard Time Time Zone UTC Offset Politics Universal Coordinated Time (UTC) Leap Seconds Celestial Mechanics International Atomic Time (ITA) Things Change Wall Time Standard Offset changes ~ 2 / year Standard Time Time Zone UTC Offset changes ~ 10 / year Universal Coordinated Time (UTC) 27 changes so far Leap Seconds last was in Dec 2016 ~ 37 seconds International Atomic Time (ITA) "Time Zone" How Elixir Represents Time Date Time year hour month minute day second nanosecond NaiveDateTime Date Time year hour month minute day second nanosecond DateTime time_zone NaiveDateTime utc_offset std_offset zone_abbr Date Time year hour month minute day second -
Operation Guide 3448
MO1611-EA © 2016 CASIO COMPUTER CO., LTD. Operation Guide 3448 ENGLISH Congratulations upon your selection of this CASIO watch. Warning ! • The measurement functions built into this watch are not intended for taking measurements that require professional or industrial precision. Values produced by this watch should be considered as reasonable representations only. • Note that CASIO COMPUTER CO., LTD. assumes no responsibility for any damage or loss suffered by you or any third party arising through the use of your watch or its malfunction. E-1 About This Manual • Keep the watch away from audio speakers, magnetic necklaces, cell phones, and other devices that generate strong magnetism. Exposure to strong • Depending on the model of your watch, display text magnetism can magnetize the watch and cause incorrect direction readings. If appears either as dark figures on a light background, or incorrect readings continue even after you perform bidirectional calibration, it light figures on a dark background. All sample displays could mean that your watch has been magnetized. If this happens, contact in this manual are shown using dark figures on a light your original retailer or an authorized CASIO Service Center. background. • Button operations are indicated using the letters shown in the illustration. • Note that the product illustrations in this manual are intended for reference only, and so the actual product may appear somewhat different than depicted by an illustration. E-2 E-3 Things to check before using the watch Contents 1. Check the Home City and the daylight saving time (DST) setting. About This Manual …………………………………………………………………… E-3 Use the procedure under “To configure Home City settings” (page E-16) to configure your Things to check before using the watch ………………………………………… E-4 Home City and daylight saving time settings. -
GLONASS Time. 2. Generation of System Timescale
GLONASS TIME SCALE DESCRIPTION Definition of System 1. System timescale: GLONASS Time. 2. Generation of system timescale: on the basis of time scales of GLONASS Central Synchronizers (CS). 3. Is the timescale steered to a reference UTC timescale: Yes. a. To which reference timescale: UTC(SU), generated by State Time and Frequency Reference (STFR). b. Whole second offset from reference timescale: 10800 s (03 hrs 00 min 00 s). tGLONASS =UTC (SU ) + 03 hrs 00 min c. Maximum offset (modulo 1s) from reference timescale: 660 ns (probability 0.95) – in 2014; 4 ns (probability 0.95) – in 2020. 4. Corrections to convert from satellite to system timescale: SVs broadcast corrections τn(tb) and γn(tb) in L1, L2 frequency bands for 30-minute segments of prediction interval. a. Type of corrections given; include statement on relativistic corrections: Linear coefficients broadcast in operative part of navigation message for each SV (in accordance with GLONASS ICD). Periodic part of relativistic corrections taking into account the deviation of individual SVs orbits from GLONASS nominal orbits is incorporated in calculation of broadcast corrections to convert from satellite timescale to GLONASS Time. b. Specified accuracy of corrections to system timescale: The accuracy of calculated offset between SV timescale and GLONASS Time – 5,6 ns (rms). c. Location of corrections in broadcast messages: L1/L2 - τn(t b) – line 4, bits 59 – 80 of navigation frame; - γn(t b) - line 3, bits 69 – 79 of navigation frame. d. Equation to correct satellite timescale to system timescale: L1/L2 tGLONASS = t +τ n (tb ) − γ n (tb )( t − tb ) where t - satellite time; τn(t b), γn(tb) - coefficients of frequency/time correction; tb - time of locking frequency/time parameters. -
International Earth Rotation and Reference Systems Service (IERS) Provides the International Community With
The Role of the IERS in the Leap Second Brian Luzum Chair, IERS Directing Board Background The International Earth Rotation and Reference Systems Service (IERS) provides the international community with: • the International Celestial Reference System and its realization, the International Celestial Reference Frame (ICRF); • the International Terrestrial Reference System and its realization, the International Terrestrial Reference Frame (ITRF); • Earth orientation parameters (EOPs) that are used to transform between the ICRF and the ITRF; • Conventions (i.e., standards, models, and constants) used in generating and using reference frames and EOPs; • Geophysical data to study and understand variations in the reference frames and the Earth’s orientation. The IERS was created in 1987 and began operations on 1 January 1988. It continued much of the tasking of the Bureau International de l’Heure (BIH), which had been created early in the 20th century. It is responsible to the International Astronomical Union (IAU) and the International Union of Geodesy and Geophysics (IUGG). For more than twenty-five years, the IERS has been providing for the reference frame and EOP needs of a variety of users. Time The IERS has an important role in determining when the leap seconds are to be inserted and the dissemination of information regarding leap seconds. In order to understand this role, it is important to realize some things regarding time. For instance, there are two different kinds of “time” being related: (1) a uniform time, now based on atomic clocks and (2) “time” based on the variable rotation of the Earth. The differences between uniform time and Earth rotation “time” only became apparent in the 1930s with the improvements in clock technology. -
Role of the IERS in the Leap Second Brian Luzum Chair, IERS Directing Board Outline
Role of the IERS in the leap second Brian Luzum Chair, IERS Directing Board Outline • What is the IERS? • Clock time (UTC) • Earth rotation angle (UT1) • Leap Seconds • Measures and Predictions of Earth rotation • How are Earth rotation data used? • How the IERS provides for its customers • Future considerations • Summary What is the IERS? • The International Earth Rotation and Reference Systems Service (IERS) provides the following to the international scientific communities: • International Celestial Reference System (ICRS) and its realization the International Celestial Reference Frame (ICRF) • International Terrestrial Reference System (ITRS) and its realization the International Terrestrial Reference Frame (ITRF) • Earth orientation parameters that transform between the ICRF and the ITRF • Conventions (i.e. standards, models, and constants) used in generating and using reference frames and EOPs • Geophysical data to study and understand variations in the reference frames and the Earth’s orientation • Due to the nature of the data, there are many operational users Brief history of the IERS • The International Earth Rotation Service (IERS) was created in 1987 • Responsible to the International Astronomical Union (IAU) and the International Union of Geodesy and Geophysics (IUGG) • IERS began operations on 1 January 1988 • IERS changed its name to International Earth Rotation and Reference Systems Service to better represent its responsibilities • Earth orientation relies directly on having accurate, well-defined reference systems Structure -
GPS Operation V1 4.Fm
Operation of the Courtyard CY490 SPG While Connected to the GPS Receiver No part of this document may be transmitted or reproduced in any form or by any means, electronic or mechanical, including photocopy, recording or any information storage and retrieval system, without permission in writing from Courtyard Electronics Limited. Introduction One of the best sources of reference for both frequency and time, is the Global Positioning System. The GPS system only transmits a complete UTC-GPS time message once every 12.5 minutes. So when powering up the GPS receiver it might be best to wait 12.5 minutes before relying on the GPS time. The CY490 SPG uses a 12 channel GPS receiver. As the SPG is powered the GPS receiver begins searching for satellites from which it can get time, frequency and phase information. In a good reception area as many as 12 satellites may be visible. The SPG only requires 3 satellites to be located and fully decoded before it can start using the GPS data. The search for the first 3 satellites can take up to 3 minutes, but is often accomplished in 2. If less than 3 satellites are available, the SPG will not lock to GPS. The number of satellites can be monitored on the first menu and on the remote control program CY490MiniMessage. The CY490MiniMessage gives a graphic view of satellites and provides much information for the user. GPS and television From a GPS receiver, the Master Clock can derive UTC and also add the appropriate time offset and provide corrected local time. -
Concern on UTC Leap Second Schedule Announcements
Concern on UTC Leap Second Schedule Announcements Karl Kovach 15 Aug 19 © 2019 The Aerospace Corporation UTC & Leap Seconds • International Earth Rotation Service (IERS) – The “keeper’ of UTC • The ‘decider’ of UTC leap seconds • U.S. Naval Observatory (USNO) – Contributes to IERS for UTC • Follows IERS for UTC leap seconds • U.S. Department of Defense (DoD) – Follows USNO for UTC & UTC leap seconds • Global Positioning System (GPS) – Should be following USNO for UTC & UTC leap seconds 2 UTC Leap Second Announcements • IERS announces the UTC leap second schedule – USNO forwards the IERS announcements • DoD uses the IERS leap second announcements – GPS should simply follow along… 3 IERS “Bulletin C” Announcements Paris, 6 July 2016 – Bulletin C 52 4 IERS “Bulletin C” Announcements Paris, 9 January 2017 – Bulletin C 53 5 IERS “Bulletin C” Announcements Paris, 06 July 2017 – Bulletin C 54 6 IERS “Bulletin C” Announcements Paris, 09 January 2018 – Bulletin C 55 7 IERS “Bulletin C” Announcements Paris, 05 July 2018 – Bulletin C 56 8 IERS “Bulletin C” Announcements Paris, 07 January 2019 – Bulletin C 57 9 IERS “Bulletin C” Announcements Paris, 04 July 2019 – Bulletin C 58 10 UTC Leap Second Announcements • IERS announces the UTC leap second schedule – USNO forwards the IERS announcements • DoD uses the IERS leap second announcements – GPS should simply follow along… • GPS also announces a UTC leap second schedule – Should be the same schedule as IERS & USNO 11 GPS Leap Second Announcement WNLSF DN ΔtLSF 12 GPS Leap Second Announcement Leap -
Leap Second Application Anomaly
PRESS RELEASE Leap Second Application Anomaly Affected products The following models will not properly apply the leap second coming 31 December 201 6. Model 1 084A/B/C Model 1 093A/B/C Model 1 1 33A Model 1 088A/B Model 1 094B Model 1 092A/B/C Model 1 095B/C What is a leap second? A leap second is the second added to or subtracted from the UTC time reference when the difference between UTC and UT1 approaches 0.9 seconds. By adding an additional second to the time count, clocks are effectively stopped for that second to give Earth the opportunity to catch up with atomic time. What does this mean, UTC, UT1 , et cetera? There are many time references in use. There is time based on atoms. There is time based on the Earth's rotation. Then there is time that we civilians use. • International Atomic Time (TAI). TAI is a statistical atomic time scale based on a large number of clocks operating at standards laboratories around the world with the unit interval of the SI second. • Universal Time (UT1 ). UT1 is also known as Astronomical Time and is the non-uniform time based on the Earth’s rotation. • Coordinated Universal Time (UTC) is a widely used standard for international timekeeping of civil time and differs from TAI by the total number of leap seconds. • Global Positioning System (GPS) Time is the atomic time scale implemented by the atomic clocks in the GPS ground control stations and the GPS satellites themselves. GPS time was zero at 0h 6 January 1 980 and does not include leap seconds. -
15 Pecision System Clock Architecture
Pecision System Clock Architecture 15 Pecision System Clock Architecture “Time iz like money, the less we hav ov it teu spare the further we make it go.” Josh Billing Encyclopedia and Proverbial Philosophy of Wit and Humor, 1874 225 Pecision System Clock Architecture Limitations of the Art Over the almost three decades that NTP has evolved, accuracy expectations have improved from 100 ms to less than 1 ms on fast LANs with multiple segments interconnected by switches and less than a few milliseconds on most campus and corporate networks with multiple subnets interconnected by routers. Today the practical expectations with a GPS receiver, PPS signal and precision kernel support are a few microseconds. In principle the ultimate expectations are limited only by the 232-ps resolution of the NTP timestamp format or about the time light travels three inches. Improving accuracy expectations below the PPS regime is proving intricate and tricky. In this chapter we turn to the most ambitious means available to minimize errors in the face of hardware and software not designed for extraordinary timekeeping. First we examine the hardware and software components for a precision system clock and evolve an optimal design. Next we survey timestamping techniques using both hardware, driver and software methods to minimize errors due to media, device and operating system latencies. Finally, we explore the IEEE 1588 Precision Time Protocol (PTP), how it is used in a high speed LAN, and how it and NTP can sail in the same boat. The parting shots section proposes a hardware assisted design which provides performance equivalent to PTP with only minimal modifications to the Unix operating system kernel. -
Kronosync® Transmitter Operations Guide
KRONOsync Transmitter System Operations Guide 11869 Teale St. Culver City, CA 90230 Tech Support: 888-608-0125 www.InnovationWireless.com System Operations Guide Thank You for Purchasing the KRONOsync GPS/NTP Wireless Clock System from Innovation Wireless. We appreciate having you as a customer and wish you many years of satisfied use with your KRONOsync clock system. Innovation Wireless has incorporated our 40+ years of experience in clock manufacturing with the best of today’s innovative technology into the KRONOsync system. The result being an accurate, reliable, ‘Plug and Play’, wireless clock system for your facility. Please read this manual thoroughly before making any connections and powering up the transmitter. Following these instructions will enable you to obtain optimum performance from the KRONOsync Wireless Clock System. If you have any questions during set-up, please contact Technical Support at 1-888-608-0125. Thank you again for your purchase. From all of us at Innovation Wireless 2 | P a g e Innovation Wireless System Operations Guide System Operations Guide Table of Contents KRONOsync Transmitter Set-up .................................................................................................................... 4 Mounting the GPS Receiver .......................................................................................................................... 4 Connecting the NTP Receiver........................................................................................................................ 4 Power -
Date and Time Terms and Definitions
Date and Time Terms and Definitions Date and Time Terms and Definitions Brooks Harris Version 35 2016-05-17 Introduction Many documents describing terms and definitions, sometimes referred to as “vocabulary” or “dictionary”, address the topics of timekeeping. This document collects terms from many sources to help unify terminology and to provide a single reference document that can be cited by documents related to date and time. The basic timekeeping definitions are drawn from ISO 8601, its underlying IEC specifications, the BIPM Brochure (The International System of Units (SI)) and BIPM International vocabulary of metrology (VIM). Especially important are the rules and formulas regarding TAI, UTC, and “civil”, or “local”, time. The international standards that describe these fundamental time scales, the rules and procedures of their maintenance, and methods of application are scattered amongst many documents from several standards bodies using various lexicon. This dispersion makes it difficult to arrive at a clear understanding of the underlying principles and application to interoperable implementations. This document collects and consolidates definitions and descriptions from BIPM, IERS, and ITU-R to clarify implementation. There remain unresolved issues in the art and science of timekeeping, especially regarding “time zones” and the politically driven topic of “local time”. This document does not attempt to resolve those dilemmas but describes the terminology and the current state of the art (at the time of publication) to help guide