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THE NATIONAL STANDARD OF ELECTRIC CURRENT

Activites 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 electric current to the international level

At the moment, the SIQ is ensuring traceability of standards which provide the basis for the realisation of the national standard of electric current, i.e. the DC voltage standard and the DC resistance standards in the primary laboratory of the Nederlands Meetinstituut (NMi), the Netherlands; the AC voltage standards and the standard AC/DC shunts, in the primary laboratory of the Sveriges Provnings-och Forskningsinstitut (SP), Sweden; and in the Physikalisch-Technische Bundesanstalt (PTB), Germany. Based on the calibrations of these standards, the SIQ also calibrates other standards necessary for the realisation of the complete accredited scope for the electric current quantity. In view of improving the measurement uncertainty, the SIQ participates in numerous international inter-laboratory comparisons of the electric quantity standards.

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

The dissemination of the value by means of national standards is conducted following the accredited procedures, to the laboratory's working standards, which are then used for calibration of customers' standards. The national standards can exceptionally be used for calibrations, e.g. when uncertainties close to the best measuring capabilities of the laboratory must be met, or in inter-laboratory comparisons.

Scientific research work in the field of the quantity of electric current

The SIQ has focused its scientific research activity on the improvement of measurement uncertainty of individual quantities, on realisation of new standards, on meeting special needs of particular users of metrological services, and on participating in international scientific research projects. In the field of the electric current quantity, it conducts scientific research projects for the production of measurement standards (computable source of AC voltage, standard resistors, high-resistance scaling dividers, and methods of measurement.

Standard equipment

The national standard of electric current is realised indirectly through the realisation of standards for DC voltage, DC resistance, AC/DC transfer, and AC shunts.

Direct current:

In a DC range between 100 nA and 20 A, the unit of electric current is realised through the measurement of voltage drop on the DC resistor.

     

  • DC voltage includes 10 decadic classes of size, ranging from 1 µV to 10 kV. All values are derived from the reference value of 10 V, which is determined by a reference group of four semi-conductor voltage standards.
  • DC resistance is established through a reference group of three standard resistors of 10 k Ω. From this value, all the decadic values ranging from 0.1 m Ω to 100 T Ω are derived through scaling by resistance bridges of various types, which correspond to 18 decadic classes of size.

Alternating current:

In a frequency range between 20 Hz and 10 kHz, and current range between 100 µA and 10 A, the standard unit of electric current is realised through the use of shunts combined with thermal voltage transformers.

     

  • AC voltage is determined on the basis of known DC voltage and evaluated standards of AC/DC transfer of 2 mV to 1000 V.
  • AC resistance is represented by a group of standard AC/DC shunts of 100 µA to 10 A.