Abstract
The second, the base unit of time interval in the International System, is defined in terms of the two hyperfine states of the Cesium atom ground-state energy level. This definition has so far served the metrology community well, and the uncertainty of the best realization of the second has improved by a rate of about one order of magnitude per decade over the past 50 years, reaching a current level of a few parts in 1016 [1]. This continual reduction in uncertainty has increased the level of performance expected from both time and frequency transfer systems and from the time standards maintained by national metrology institutes (NMIs). During recent years, an automated time comparison network has been developed within the Sistema Interamericano de Metrologia (SIM), a regional metrology organization. The SIM Time Network (SIMTN) allows NMIs to compare their time scales via the Global Positioning System common-view and all-in-view time transfer techniques, and makes results available through the Internet in near real time [2]. The SIMTN has proven to be robust and reliable, and the uncertainty of its comparisons is similar to the uncertainty of the key comparisons published by the Bureau International des Poids et Mesures in its monthly Circular T document. The large number of geographically dispersed clocks measured by the SIMTN made it attractive to develop a SIM time scale (SIMT), which is computed in near real time and immediately made available to the general public via the Internet. This rapid computation allows contributing laboratories to easily monitor their time scales, and to quickly detect short term fluctuations in stability and accuracy. This paper discusses both the SIMTN and the SIMT, focusing primarily on the SIMT algorithm and the results of its performance.
Similar content being viewed by others
References
T.P. Heavner, T.E. Parker, J.H. Shirley, P. Kunz and S.R. Jefferts, NIST F1 and F2, Proceedings of the 42nd Annual Precise Time and Time Interval (PTTI) Meeting, pp. 457–463, November 2010.
M.A. Lombardi, A.N. Novick, J.M. Lopez-Romero, F. Jimenez, E. de Carlos-Lopez, J.S. Boulanger, R. Pelletier, R. de Carvalho, R. Solis, H. Sanchez, C.A. Quevedo, G. Pascoe, D. Perez, E. Bances, L. Trigo, V. Masi, H. Postigo, A. Questelles and A. Gittens, The SIM Time Network, NIST J. Res., 116 (2011) 557–572.
W.J. Riley, Handbook of Frequency Stability Analysis. NIST Special Publication 1065, July 2008.
B. Guinot, Some Properties of Algorithms for Atomic Time Scales, Metrologia, 24 (1987) 195–198.
S.R. Stein, Time Scales Demystified, Proceedings of the 2003 IEEE Frequency Control Symposium and European Frequency and Time Forum, pp. 224–227, May 2003.
J.M. López-Romero, N. Díaz-Muñoz and M.A. Lombardi, Establishment of the SIM Time Scale, Proc. 2008 Simposio de Metrología, Querétaro, México, October 2008.
J. Levine, Introduction to Time and Frequency Metrology, Rev. Sci. Instrum., 70 (1999) 2576–2596.
J.M. Lopez-Romero and N. Diaz-Munoz, Progress in the Generation of the UTC(CNM) in Terms of a Virtual Clock, Metrologia, 45 (2008) S59–S65.
M. Weiss and T. Weissert, AT2, A New Time Scale Algorithm: AT1 Plus Frequency Variance, Metrologia, 28 (1991) 65–74.
Author information
Authors and Affiliations
Corresponding author
Rights and permissions
About this article
Cite this article
López-Romero, J.M., Lombardi, M.A. & Díaz-Muñoz, N. Automated Clock Comparisons and Time Scale Generation in the SIM Region. MAPAN 27, 49–53 (2012). https://doi.org/10.1007/s12647-012-0002-4
Received:
Accepted:
Published:
Issue Date:
DOI: https://doi.org/10.1007/s12647-012-0002-4