Topic
Time deviation
About: Time deviation is a research topic. Over the lifetime, 583 publications have been published within this topic receiving 4407 citations.
Papers published on a yearly basis
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Papers
TL;DR: In this article, the authors present the results of their work concerning the long-distance fibre optic dissemination of time (1.PPS) and frequency (10MHz) signals generated by atomic sources, such as caesium clocks, hydrogen masers or caeium fountains.
Abstract: In this paper we present the results of our work concerning the long-distance fibre optic dissemination of time (1 PPS) and frequency (10 MHz) signals generated by atomic sources, such as caesium clocks, hydrogen masers or caesium fountains. For these purposes we developed dedicated hardware (a fibre optic system with active stabilization of the propagation delay and bidirectional fibre optic amplifiers) together with a procedure to enable calibration of the time transfer. Our laboratory measurements performed over fibre lengths of up to 480 km showed an Allan deviation of the order of 4 × 10−17, time deviation below 1 ps (both at one-day averaging) and the possibility of calibration with picosecond accuracy even for the longest from evaluated links. After successful laboratory evaluation the system was next installed on a 421.4 km long route between the Central Office of Measures (GUM) in Warsaw, Poland, and the Astrogeodynamic Observatory (AOS) in Borowiec near Poznan, Poland. Experiments comparing the UTC(PL) and UTC(AOS) atomic timescales using the fibre optic link and TTS-4 dual-frequency GNSS time transfer receivers showed that the consistency of the results is within the calibration accuracy of the GPS receivers and with much better noise performance. The field operation of the system proved its full functionality and confirmed our previous laboratory evaluation to the maximum extent possible using the methods for comparing distant clocks available at GUM and AOS.
208 citations
1 Jan 1984
TL;DR: In this paper, a Kalman Filter model is used to estimate and predict clock phase, frequency and frequency drift. But the model is not suitable for the measurement of phase as a function of time rather than as a spectral density.
Abstract: A relationship was constructed between the Allan variance parameters (H sub z, H sub 1, H sub 0, H sub -1 and H sub -2) and a Kalman Filter model that would be used to estimate and predict clock phase, frequency and frequency drift. To start with the meaning of those Allan Variance parameters and how they are arrived at for a given frequency source is reviewed. Although a subset of these parameters is arrived at by measuring phase as a function of time rather than as a spectral density, they all represent phase noise spectral density coefficients, though not necessarily that of a rational spectral density. The phase noise spectral density is then transformed into a time domain covariance model which can then be used to derive the Kalman Filter model parameters. Simulation results of that covariance model are presented and compared to clock uncertainties predicted by Allan variance parameters. A two state Kalman Filter model is then derived and the significance of each state is explained.
134 citations
TL;DR: In this article, a frequency counter measures the input frequency ν¯ averaged over a suitable time τ, versus the reference clock and achieves high resolution by interpolating the clock signal by averaging multiple frequency measurements highly overlapped.
Abstract: A frequency counter measures the input frequency ν¯ averaged over a suitable time τ, versus the reference clock. High resolution is achieved by interpolating the clock signal. Further increased resolution is obtained by averaging multiple frequency measurements highly overlapped. In the presence of additive white noise or white phase noise, the square uncertainty improves from σν2∝1∕τ2 to σν2∝1∕τ3. Surprisingly, when a file of contiguous data is fed into the formula of the two-sample (Allan) variance σy2(τ)=E{12(y¯k+1−y¯k)2} of the fractional frequency fluctuation y, the result is the modified Allan variance mod σy2(τ). But if a sufficient number of contiguous measures are averaged in order to get a longer τ and the data are fed into the same formula, the results is the (nonmodified) Allan variance. Of course interpretation mistakes are around the corner if the counter internal process is not well understood. The typical domain of interest is the the short-term stability measurement of oscillators.
126 citations
TL;DR: In contrast to standard two-way transfer schemes which offer only comparisons of two distant clocks, the fiber-optic frequency transfer system displays distribution functionality, reproducing the time and frequency signals of the reference clock in the remote location.
Abstract: In this paper, we describe the extension of our fiber-optic frequency transfer system to the time transfer capability. In contrast to standard two-way transfer schemes which offer only comparisons of two distant clocks, our system displays distribution functionality, reproducing the time and frequency signals of the reference clock in the remote location. By using active compensation of the fiber delay fluctuations, we obtained a time deviation of 0.3 ps (for time transfer) and an Allan deviation of 1.2 × 10-17 (for frequency transfer) at 105-s averaging. The experiments presented were carried out using a 60-km-long fiber loop, forming a part of the real urban network around Krakow.
116 citations
TL;DR: In this paper, a model sequencing algorithm for model-mix assembly lines is proposed, the objective function of which is to minimize the overall assembly line-length for no operator interference.
Abstract: SUMMARY This paper describes a model sequencing algorithm for model-mix assembly lines. A new formulation of the sequencing problem is proposed, the objective function of which is to minimize the overall assembly line-length for no operator interference. Lower bounds for the overall line-length are developed. Two types of work station interfaces are considered; ‘closed’, where boundaries cannot be violated, and ‘open’ where defined boundaries do not exist—adjacent operators being allowed to enter each others apparent work areas without causing any interference. A complete factorial experiment was made on five factors to determine their influence on the overall assembly line length. These are, the number of models, the model cycle time deviation, the production demand deviation for each model, the operator time deviation, and the number of stations in the assembly line. The main conclusions of this experiment are discussed and recommendations made for the selection of parameters used in the design of model...
112 citations
Related Topics (5)
Performance Metrics
| Year | Papers |
|---|---|
| 2021 | 17 |
| 2020 | 44 |
| 2019 | 33 |
| 2018 | 33 |
| 2017 | 39 |
| 2016 | 29 |