| Zugriffsnummer | 34585 |
| Dokumenttyp | Konferenzartikel |
| Sprache | Englisch |
| Titel | A status report on time scale generation in PTB |
| Autor(in); Institution |
Bauch, Andreas; 4.4, Zeit und Frequenz, PTB-Braunschweig
Staliuniene, Egle; 4.4, Zeit und Frequenz, PTB-Braunschweig
Gomah, Gihan; National Institute for Standards, Tersa St. Elharam, Giza, EGYPT
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| Quelle/Jahr | 2015 Joint Conference of the IEEE International Frequency Control Symposium & the European Frequency and Time Forum:(2015), 379 - 383 |
| ISBN | 978-1-4799-8866-2 |
| Berichtsnummer | CFP15FRE-ART |
| Verlag | Piscataway, NJ: IEEE |
| Konferenzangaben | 2015 Joint IEEE International Frequency Control Symposium and 29th European Frequency and Time Forum, Denver, Colo., 12-16, April, 2015, USA |
| Freie Schlagworte | scale generation ; fountain clock ; ACES ; UTC ; ALGOS process |
| Zusammenfassung | Since February 2010 UTC(PTB) has been realized using an active hydrogen maser as signal source whose frequency is steered via a commercial high resolution offset generator. Steering is based primarily on the comparison between the maser involved and PTB’s primary fountain clocks CSF1 and CSF2 [1]. In the long term, UTC(PTB) is steered towards UTC based on the data published in the BIPM Circular T. Between July 2010 and July 2014 the time difference UTC – UTC(PTB) was always less than 9 ns and typically below 5 ns. During that period the maximum absolute rate of UTC UTC(PTB) during any standard 5-day interval was 0.44 ns/d. In our paper we discuss further properties of UTC(PTB) and of TA(PTB) that is generated in a similar way (but no time steering to an external reference). UTC(PTB) serves as the basis for all of PTB’s time services and international time comparisons. It will also serve directly as the time and frequency reference for the future ACES campaign [2], and we are going to describe the signal interface to the future location of the ACES microwave-link ground terminal. From early on it was foreseen that the steering of UTC(PTB) could also be derived from the ensemble of caesium beam clocks operated in PTB, described as Option 2 in [1]. It turned out that CSF1 and CSF2 provided data with greatest reliability so that this option needed hardly ever be applied, UTC(PTB) practically is a fountain-based time scale. Since several months a timescale generation “test bed” is used to realize another time scale, named UTT(PTB), based on the inputs of five thermal beam clocks. Contrary to the expectations, a considerable difference between UTC(PTB) and UTT(PTB) was noted and motivated a study into the causes thereof. The steering commanded to the UTT(PTB) phase stepper consists of two clock specific summands and a common term, δfSteer = wi\{δfClock(i) + δfRate(i)\} + δfOffset. The term δfClock(i) is the predicted frequency offset of clock(i) from the maser used to generate UTT(PTB) for the current day, based on 16 or 25 days averaging, depending on the clock type. δfRate(i) is the rate of clock(i) with respect to TAI, and the weight wi (weights normalized to 1) has been calculated based on the weights of the clocks in the ALGOS process, both quantities published monthly by BIPM. δfOffset has been determined so that a time offset UTT(PTB) UTCr that appears at the end of a week is steered to zero within 20 days. Our analysis based on a few months of data showed that the averaging times mentioned should be changed, and in particular that the statistical weights published by BIPM deviate substantially from values that one would generate autonomously based on the instability of the clock frequency prediction. The findings will be explained in details. Starting January 2015, UTT(PTB) will be generated using the new strategy, and first results will be available at the time of the conference. |
