# Direct Current

## Realization of the unit Direct Current

The unit of electric current is a base unit:

“The ampere (A) is defined as that constant current which, if maintained in two straight parallel conductors of infinite length, of negligible circular cross-section, and placed 1 metre apart in vacuum, would produce between these conductors a force equal to 2 x 10–7 newton per metre of length”.

As this definition is metrologically unfeasible, in practice, electric current is reduced to the accurately measurable quantities direct voltage and resistance as stated by Ohm’s Law

(I = U / R).

The following method is applied at BEV: the current (I) to be measured is sent through a resistance (R) and at the same time the voltage drop (U) at the terminals is measured with a voltmeter.

A calibrated resistance and a calibrated voltmeter with known values are used for this.

The value of the current measured can be calculated applying Ohm’s Law.