# References of electrical quantities

## DEFINITION

The ampere, symbol A, is the SI unit of electric current. It is defined by taking the fixed numerical value of the elementary charge e to be 1.602 176 634×10^{–19} when expressed in the unit C, which is equal to A s, where the second is defined in terms of ∆*ν*_{Cs}.

## REALISATION OF THE SCALE

In the Estonian national electrical quantities’ measurement standard laboratory the unit of current is expressed via direct voltage unit Volt and resistance unit Ohm. A direct current unit Volt is realised by means of Zener-type reference voltage sources at reference values 1 V and 10 V. An electrical resistance unit Ohm is realised by using a set of precision resistors in the range from 1 mΩ to 10 kΩ. See the approved list of national measurement standards.

## DEVICES AND POSSIBILITIES

For offering a calibration service, reference voltage sources Fluke 7000 and 732B, voltage divider Fluke 752A, multifunctional calibrator Fluke 5720A, precision resistors Tinsley 5685 and an automatic measuring bridge MI 6010B are used.

Measuring instruments that measure direct voltage are calibrated in the range from 10 mV to 1 kV with a relative expanded uncertainty of (1…20)·10^{-6}.

Measuring instruments that measure resistance are calibrated in the range from 1 mΩ to 10 kΩ with a relative expanded uncertainty of (1…5)·10^{-6}.

## ADDITIONAL INFORMATION

Andrei Pokatilov

Phone +372 5 297 095

E-mail andrei.pokatilov@metrosert.ee