GROUP FOR TIME, FREQUENCY AND TIME DISSEMINATION
Activities and tasks
- Keeping and maintenance of the time and frequency unit measurement standards and transferring of the time and frequency unit
- Realization of the national time scale, providing preconditions for its dissemination, dissemination and dissemination control
- Development and upgrading of metrological qualities of the national time and frequency standard and providing of its participation in international activities
- Development and application of new methods of transferring of the time and frequency units
- Calibration of reference time and frequency standards
- Establishing traceability in speed measurements
- Type examination of measuring instruments for measurement of the speed of vehicles
- Initiating and preparation of the regulations in the field of time, frequency and speed measurements
The main task of the Laboratory for time and frequency is to establish and maintain national time scale. It comprehends the realization of the time unit – second and the time scale, as a continuous time reference.
The national time and frequency standard is a system of which the most important part is an atomic caesium beam standard. The standard is placed in a Faraday cage to reduce influences of the electromagnetic field down to 100 dB, temperature variances are ± 0,5 °C. The uninterrupted power source with an autonomy of 24 hours provides reliable and quality powering.
The national time and frequency standard has a triple role: as a time unit – second standard, as a source of the national time scale UTC(DMDM) and as a source of reference frequencies.
Universal Coordinated Time (UTC) is a worldwide used time scale, being locally corrected depending on the longitude and daylight saving. UTC time scale is derived from the International Atomic Time (TAI) scale. TAI is a scale that is computed based on time comparison data of more than 400 atomic clocks, sent by over 60 laboratories from all over the world; by January 2006 our laboratory being one of them.
For that purpose, continuous measurements are performed on a daily basis – comparison of the time of our clock to the GPS time, i.e. time of the onboard satellite clocks of the Global Positioning System, using the appropriate GPS receiver and the measuring system for the comparison. Every fifth day, on standard MJD dates, this (master) clock is compared to the other (redundant) caesium clock of the same type, so our laboratory contribute to TAI with two caesium cloks. At the same time, it is a key comparison, denoted CCTF-K001.UTC.
Results of our measurements are published in BIPM monthly bulletin Circular-T.
Average frequency offset of the clock, relative to the international time reference, computed from the Circular-T, is about -7x10-14, which is more than one order of magnitude better than specified.
Frequency stability of the caesium frequency standard
Calibration and measurement capabilities (СМСs)
Calibration and measurement capabilities (CMCs) for time and frequency are published in the data base of the Bureau International des Poides et Mesures. Dissemination of the official time in the Republic of Serbia
DMDM is responsible for the dissemination of the official time in Serbia according to the Article 7, Item 13, of the Law on Metrology.
Official time in the Republic of Serbia is Universal Coordinated Time (UTC) plus one hour (Central European Time), in respect of which daylight saving time is introduced from the last Sunday in March to the last Sunday in October, according to Articles 1 and 2 of the Law on Time.
UTC is the world time scale that has only local physical realisations traceable to UTC. UTC (DMDM) is national realisation of UTC in the Republic of Serbia (derived from national time and frequency standard - atomic clocks in DMDM), and represents the official time in the Republic of Serbia. In the year 2011, the difference between UTC (DMDM) and UTC was in the range of ± 35 nanoseconds.
DMDM disseminates UTC (DMDM) over the internet using NTP protocol (Network Time Protocol) for synchronisation of the client’s PC clock with the referent clock.
Time data are disseminated by means of two public Stratum 2 time servers, each connected to one of two Stratum 1 time servers. Stratum 1 servers are connected to the national time and frequency standard. The host names of the public NTP-servers are:
For synchronisation of client’s PC clock with these servers, client’s PC needs software that supports NTP protocol. Such software is developed for all main operating systems.
Some applications that may be used for the communication with public servers:
Applications may be downloaded from:
Synchronisation time interval should be adjusted in the application. Choosing interval of 1 hour is sufficient to keep client clock second indication accurate. Synchronisation interval should not be shorter than 10 min.
Accuracy of the synchronisation via NTP depends mainly on the speed of the internet connection, the number of computers that simultaneously requests synchronisation, the distance from the server and the quality of the internet connection. Access to Stratum 1 time servers, with verification of authenticity of the disseminated time data, is permitted to authorised clients only. Note:
DMDM assumes no liability for any damage caused to users by failure of the time service, by incorrect transmission by the DMDM public time server, or by deviations in consequence of delays in the internet.
DMDM in any case shall not be liable for any damages in regarding the use of or downloading of data from public time servers, and particularly in relation to providing quality links to the user. Daylight Saving Time
Daylight Saving Time was introduced in 1983, start and end dates being established yearly by the act of the ministry until the year 2006, when it was regulated by the Low on time to be last Sundays in March and October. Projects
The laboratory for time took part in 2005. within the EUROMET project #828. The aim of this project was the comparison of the time interval measurements, and 25 national laboratories took part in this project.
The laboratory also took part in the GPS equipment calibration campaign, organized by BIPM, in December 2006.
In 2008, the laboratory took part in the EURAMET project #1017 that had the goal of presenting laboratories for time and frequency.
In 2009. the laboratory took part in the EURAMET project #1018 with the purpose of establishing data base on the satellite receivers used for time transfer in European national laboratories for time and frequency, and the EURAMET project #1117 with the task to make a survey of European countries' legal time regulations and practices. Contact
Head of Group for time, frequency and time dissemination Snezana Renovica, dipl.ing.
Phone: +381 11 20 24 407
Fax: +381 11 21 81 668
Phone: +381 11 20 24 406
Fax: +381 11 21 81 668
Group for time, frequency and time dissemination
Mike Alasa 14,
Republic of Serbia