Metrological and Legal Traceability of Time Signals

Abstract

Metrological traceability requires an unbroken chain of calibrations that relate to a reference, with each calibration having a documented measurement uncertainty. In the field of time and frequency metrology, the desired reference is usually Coordinated Universal Time (UTC), or one or more of its official realizations, termed UTC(k), and traceability to UTC is a legal requirement for many entities. Traceability to UTC can be established in three areasfrequency, time interval, and timeof-day synchronization, but this paper focuses solely on the traceability of time signals used for synchronization. We first examine the definition of traceability, then discuss how traceability can be established via the reception of time signals transmitted by satellites and network time servers, followed by a discussion of how these signals can meet the synchronization and traceability requirements of the financial and electric power industries. Not all of the available UTC time signals are considered in this paper, as we primarily focus on direct broadcast and common-view Global Positioning System (GPS) signals, with uncertainties measured in nanoseconds, and Network Time Protocol (NTP) signals, with uncertainties measured in microseconds and milliseconds.

On the possibility of getting traceable time and frequency measurements via GNSS receivers

“…During recent years, the three timescales have deviated by less than 5 ns so that the information in the navigation message can de facto be considered as a good prediction for all of them. By US legislation, the reception of GPS establishes the required legal traceability path (Matsakis et al 2018). In their paper, the authors also advertise services provided by NIST, for establishing a link to UTC(NIST).…”

“…There is an ongoing debate on how traceability to national or international standards can be established with reasonable effort using such instrumentation, as reflected in the title of this paper. PTB shares common consensus that "something has to be done" (Lombardi 2016;Matsakis et al 2018;Piester et al 2019a), and in the section on recording and documentation of GNSS signals in PTB, our approach is provided for discussion. Looking ahead, improvements in the quality of time comparisons are needed to keep up with the ongoing improvements of atomic clocks.…”

Design and Development of a Cyber Security Framework for National Time Dissemination

“…These signs have small adequate uncertainties to address industrial synchronization and traceability necessities, but users are accountable for having adequate evidence to show that their necessities are being addressed. Matsakis et al [44] pointed out that an important part of this signal is the capability to exhibit that an uninterrupted sequence of calibrations back to UTC through a UTC (k) laboratory subsists, and that every linkage of the traceability chain has a standard measurement uncertainty. Figure 4 illustrates about timescale management system.…”

An evaluation of dependencies of critical infrastructure timing systems on the global positioning system (GPS)

“…Systems that physically realize the units, by generating time or time signals, will of course introduce some measurement uncertainty. Because UTC is the world's best physical approximation of the SI second, all time and frequency measurements should be referenced to UTC, and all traceability chains should originate with UTC [24]. However, as previously noted, UTC is not a physical standard, and actual time measurements will need to be made with respect to one of the local UTC(k) time scales, such as UTC(NIST) in the United States.…”