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Search Publications by: Michael A. Lombardi (Assoc)

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Displaying 26 - 50 of 146

International Comparisons of Network Time Protocol Servers

December 4, 2014
Author(s)
Michael A. Lombardi, Judah Levine, Jose M. Lopez, Francisco Jimenez, John Bernard, Marina Gertsvolf, Harold Sanchez, Oscar G. Fallas, Liz C. Hernandez Ferero, Ricardo de Carvalho, Mario Fittipaldi, Raul Solis, Franklin Espejo
This paper describes a recently designed system that measures the time transmitted by network time protocol (NTP) servers located in North, Central, and South America. Direct measurements of the time transmitted by each server are obtained by comparing the

A Low-Cost Time Transfer Receiver for Contributions to Coordinated Universal Time

November 6, 2014
Author(s)
Michael A. Lombardi, Andrew N. Novick, Victor S. Zhang
This paper describes a low-cost time transfer receiver that allows timing laboratories, including national metrology institutes and other designated institutions, to contribute data to the computation of Coordinated Universal Time (UTC). The time transfer

Improvements in SIM Time Network and SIM Time Scale Performance

October 10, 2014
Author(s)
Michael A. Lombardi, J. Mauricio Lopez-Romero, Nelida Diaz-Munoz, E. de Carlos-Lopez, Marina Gertsvolf, Ricardo de Carvalho
We report recent results achieved within the Sistema Interamericano de Metrología (SIM) regarding the multinational cooperation program in the field of time and frequency metrology. We discuss the performance of the SIM Time Network (SIMTN) and the SIM

WWVB: A Half Century of Delivering Accurate Frequency and Time by Radio

March 12, 2014
Author(s)
Michael A. Lombardi, Glenn K. Nelson
In commemoration of its 50th anniversary of broadcasting from Fort Collins, Colorado, this paper provides a history of National Institute of Standards and Technology (NIST) radio station WWVB. The narrative describes the evolution of the station, from its

Frequency Measurement

February 3, 2014
Author(s)
Michael A. Lombardi
An overview of frequency metrology, with emphasis on estimating accuracy and stability, oscillator types, and measurement instrumentation. It describes how to measure frequency and the statistics and terminology that are used to report the results. The

Time Measurement

February 3, 2014
Author(s)
Michael A. Lombardi
An overview of time metrology, with emphasis on time interval measurements, and time synchronization. It covers the evolution of clocks and timekeeping, time scales, the fundamentals of time measurement, and the various time transfer technique used to

Automated Control of National Time Standards via the SIM Time Scale

September 27, 2013
Author(s)
Michael A. Lombardi, J. Mauricio Lopez-Romero, Nelida Diaz-Munoz
This paper describes a frequency and time control system developed by the Sistema Interamericano de Metrologia (SIM). Due to limited resources, some SIM national metrology institutes maintain a low-cost rubidium clock as their national time standard

The SIM time scale

April 20, 2013
Author(s)
Michael A. Lombardi, J. Mauricio Lopez-Romero, Nelida Diaz-Munoz, E. de Carlos-Lopez
Time measurement is of great importance for science, technology and commerce. Among the seven base units of the International System (SI), the second can be realized with the smallest uncertainty, currently reaching parts in 10 16. Keeping track of the

Replicating UTC(NIST) at Remote Sites

November 26, 2012
Author(s)
Michael A. Lombardi, Andrew N. Novick, J. Mauricio Lopez-Romero, Rodrigo Ramos
The National Institute of Standards and Technology (NIST) is deploying disciplined oscillators that are referenced to the UTC(NIST) time scale through common-view observations of Global Positioning System (GPS) satellites. We present measurement results

The Need for a Robust, Precise Time and Frequency Alternative to GNSS

November 1, 2012
Author(s)
Michael A. Lombardi, Mitch Narins, Per Enge, Ben Peterson, Sherman Lo, Yu-Hsuan Chen, Dennis Akos
Positioning, Navigation, and Timing (PNT) services are key enablers of both essential safety and security applications and economically beneficial capacity and efficiency applications worldwide. Whether users are ground-based, sea-based or in the air

Microsecond Accuracy at Multiple Locations: Is it possible without GPS?

October 1, 2012
Author(s)
Michael A. Lombardi
The microsecond is the most discussed unit in industrial timing systems, because microsecond accuracy is required to support critical infrastructure. Most critical infrastructure timing systems depend upon GPS, simply because microsecond accuracy is easy

International time and frequency comparisons in real time: recent results

July 2, 2012
Author(s)
Michael A. Lombardi, J. Mauricio Lopez-Romero, Nelida Diaz-Munoz, Eduardo de Carlos Lopez
Within the Sistema Interamericano de Metrologia (SIM) region, a time comparison network, SIMTN, has been developed. The SIMTN continuously compares the time scales of SIM members and publishes measurement results in near real-time. The measurements are

A new algorithm for clock weights for the SIM time scale

May 24, 2012
Author(s)
Michael A. Lombardi, J. Mauricio Lopez-Romero, Nelida Diaz-Munoz, E. de Carlos-Lopez
A time and frequency comparison system has been developed for the Sistema Interamericano de Metrologia (SIM) region in order to compare in real time the time references maintained at the SIM national metrology institutes (NMIs). Since January 2010 a

Automated Clock Comparisons and Time Scale Generation in the SIM Region

April 21, 2012
Author(s)
Michael A. Lombardi, J. Mauricio Lopez-Romero, Nelida Diaz-Munoz
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 energy level. This definition has so far served the metrology community well, and the uncertainty of the best

The Evolution of Time Measurement Part V: Radio Controlled Clocks

April 1, 2012
Author(s)
Michael A. Lombardi
A historical article about the origins and the development of radio controlled clocks (Part IV of a IV-part series). It describes the first time signal radio stations, the early use of telegraphic time codes, and the modern use of digital time codes. It

The Evolution of Time Measurement, Part 2 - Quartz Clocks

October 1, 2011
Author(s)
Michael A. Lombardi
A historical article about the origins and the development of quartz clocks and oscillators (Part II of a IV-part series). It describes the discovery of piezoelectricity, the development of the first quartz oscillators, how quartz oscillators were

An Interlaboratory Stopwatch Comparison in the SIM Region

September 1, 2011
Author(s)
Michael A. Lombardi, Raul Solis, Harold Sanchez, J. Mauricio Lopez-Romero, Francisco Jimenez, Henry Postigo, Daniel Perez, Walter Adad, Victor Masi, Ahmed Ibrahim, Bill Hoger, Ricardo de Carvalho, Jose L. Kronenberg, Gustavo C. Orozco, Theodore Reddock, Leonardo Trigo
Stopwatches and timers are used for an almost unlimited number of applications and are among the most common devices calibrated by metrology laboratories. In large nations, stopwatch calibrations are typically handled by secondary laboratories, such as

Real-Time Generation of the SIM Time Scale (SIMT) from International Clock Comparisons

August 13, 2011
Author(s)
Michael A. Lombardi, Jose M. Lopez, Andrew N. Novick, Francisco Jimenez, Nelida Diaz-Munoz, Eduardo de Carlos Lopez, Jean-Simon Boulanger, Raymond Pelletier, Ricardo de Carvalho, Raul Solis, Harold Sanchez, Liz C. Forero, Junior Gordon, Daniel Perez, Eduardo Bances, Leonardo Trigo, Victor Masi, Henry Postigo, Anthony Questelles, Anselm Gittens, Rodrigo Ramos P.
The Sistema Interamericano de Metrologia (SIM) is one of the world’s five major regional metrology organizations (RMOs). The SIM members are the national metrology institutes (NMIs) located in the 34 nations of the Organization of American States (OAS)

The SIM Time Network

March 1, 2011
Author(s)
Michael A. Lombardi, Andrew N. Novick, J. Mauricio Lopez-Romero, Francisco Jimenez, Eduardo de Carlos Lopez, Jean-Simon Boulanger, Raymond Pelletier, Ricardo de Carvalho, Raul Solis, Harold Sanchez, Carlos A. Quevedo, Gregory Pascoe, Daniel Perez, Eduardo Bances, Leonardo Trigo, Victor Masil, Henry Postigo, Anthony Questelles
The Sistema Interamericano de Metrologia (SIM) is a regional metrology organization (RMO) whose members are the national metrology institutes (NMIs) located in the 34 nations of the Organization of American States (OAS). The SIM/OAS region extends