Time metrology
Time metrology or time and frequency metrology is the application of metrology for time keeping, including frequency stability.[1][2] Its main tasks are the realization of the second as the SI unit of measurement for time and the establishment of time standards and frequency standards as well as their dissemination.[3]
Time transfer
Time transfer is a scheme where multiple sites share a precise reference time. Time transfer solves problems such as astronomical observatories correlating observed flashes or other phenomena with each other, as well as cell phone towers coordinating handoffs as a phone moves from one cell to another. Multiple techniques have been developed, often transferring reference clock synchronization from one point to another, often over long distances. Accuracy approaching one nanosecond worldwide is economically practical for many applications. Radio-based navigation systems are frequently used as time transfer systems.
In some cases, multiple measurements are made over a period of time, and exact time synchronization is determined retrospectively. In particular, time synchronization has been accomplished by using pairs of radio telescopes to listen to a pulsar, with the time transfer accomplished by comparing time offsets of the received pulsar signal.See also
- Allan variance
- Atomic clock
- Chronometry
- Clock drift
- Coordinated Universal Time
- Frequency drift
- History of timekeeping devices
- Horology
- International Bureau of Weights and Measures
- International Earth Rotation and Reference Systems Service
- Time and Frequency Standards Laboratory
- Time deviation
References
- ↑ Arias, Elisa Felicitas (2005-07-02). "The metrology of time". Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences (The Royal Society) 363 (1834): 2289–2305. doi:10.1098/rsta.2005.1633. ISSN 1364-503X. PMID 16147510. Bibcode: 2005RSPTA.363.2289A.
- ↑ Levine, Judah (1999). "Introduction to time and frequency metrology". Review of Scientific Instruments (AIP Publishing) 70 (6): 2567–2596. doi:10.1063/1.1149844. ISSN 0034-6748. Bibcode: 1999RScI...70.2567L.
- ↑ "time and frequency". https://www.bipm.org/metrology/time-frequency/.
Further reading
- IEEE Guide for Measurement of Environmental Sensitivities of Standard Frequency Generators (Revision of IEEE Std 1193 - 1994), Piscataway, NJ, USA: IEEE, doi:10.1109/ieeestd.2004.94440, ISBN 0-7381-3711-1
- IEEE Standard Definitions of Physical Quantities for Fundamental Frequency and Time Metrology—Random Instabilities, Piscataway, NJ, USA: IEEE, doi:10.1109/ieeestd.2008.4797525, ISBN 978-0-7381-6855-5
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