Coaxial Shunts as AC-DC Transfer Standards of Current

A new type of coaxial shunt, with nominal current ranges from 20 mA to 20 A, has been designed at the Istituto Nazionale di Ricerca Metrologica (INRIM). Depending on the nominal current, different construction methods have been employed. For current ranges between 100 mA and 20 A, the shunts are made using disk structures, either with surface mount (SMD) resistors or resistive layers. To reduce coupling, the structures have a very small magnetic interaction between the input current and the output voltage circuits, resulting in a flat response over a wide frequency range. This paper presents design and construction details of these shunts, as well as measurement results and plans for further development.