Patent ID: 7167556

Claim:
An electric device ( 201 , 301 ) for connecting an analogue data transfer device ( 202 ) by means of a control unit ( 203 ) to a digital transfer system, comprising means for connecting to a data transfer device with a twin cable ( 204 ), characterized in that it comprises a current amplifier arrangement ( 214 , 314 , 340 ) for looping a certain current fed into the twin cable from its other end, a first current switching device ( 219 ) for switching a first control current to the current amplifier arrangement, and a second current switching device ( 220 ) for switching a second control current to the current amplifier arrangement, wherein an impedance of a flowing path of the first control current in said first current switching device and an impedance of a flowing path of the second control current in said second current switching device make an electrical potential of said current amplifier arrangement to float in respect of a supply voltage of the electric device.