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THE NATIONAL STANDARD OF TIME AND FREQUENCY

Activities of the Slovenian Institute of Quality and Metrology - SIQ

The Slovenian Institute of Quality and Metrology (SIQ) operates as an independent, impartial and non-profit-distributing organisation in the field of metrology (holder of the national standards of electric current and of time and frequency, and a calibration laboratory), as well as in the fields of testing and certification of electrical and electronic devices, and assessment and certification of management systems.

The beginnings of the SIQ activities go back to the year 1960, when a specialised industrial institute under the name of "Institute of Automation" was founded, which included the development units of the Iskra factories, and became a common R&D organisation for the entire Iskra group. In a special "Measurement and Quality Department", as a central testing and metrology laboratory of Iskra, the Institute started to systematically develop quality testing, measuring techniques and maintenance of measuring instruments. Later on, this department became an independent organisation named the Institute of Quality Tests and Metrology (IKM), which was renamed into the Slovenian Institute of Quality and Metrology (SIQ) in 1992. The SIQ is designed following the model of this type of institutions in Europe and in the world, and in accordance with the requirements of the relevant standards.

Ensuring traceability of the national standard of time and frequency to the international level

The SIQ ensures the traceability of the standard which provides the basis for the realisation of the national standard of time and frequency, by measuring the time signals from the GPS (*) by an adequate receiver and time interval counter. The deviations of reference oscillators in the GPS satellites are continuously corrected by the United States Naval Observatory (USNO), which, besides the US National Institute of Standards and Technology (NIST) and the International Bureau of Weights and Measures (BIPM), publishes their actual values on the websites.

Dissemination of the value of the national standard to the lower hierarchical levels in Slovenia

The SIQ calibrates its measurement standards and those of other users by the signal from the national standard of time and frequency.

Scientific research work in the field of the quantity of time and frequency

In the field of the time and frequency quantity, the SIQ projects are focused on frequency distribution via optical fibres, on improvement of measurement uncertainty of the unit of time, and on direct performance of comparisons via the GPS. In this field, the SIQ plays a very important role within the framework of the EUROMET projects.

Standard equipment

The national standard of time and frequency is designed as a commercial caesium reference oscillator whose frequency is divided in such a way that the output signal has a pulse form with a period of 1 second. The period of output pulses represents the realisation of the unit of time interval (second), while the oscillator frequency (5 MHz or 10 MHz) represents the realisation of frequency.

The one-second period pulses are continuously compared with the one-second period pulses from the satellite signal receiver of the GPS. The measurements are made each full hour by taking 1000 samples each time and determining the mean value of the time interval between the signal from the GPS receiver and that from the time and frequency standard. The measurement results for each period of three months are also evaluated by a foreign national laboratory (IEN, Italy). In this way the value of the unit of time (time interval) and frequency is constantly defined, and traceability to the international level is ensured.