Patent ID: 7525314

Claim:
An apparatus for active compensation of magnetic and/or electromagnetic interference fields in a predetermined volume comprising at least one Helmholtz coil, which essentially encloses this volume, and a device for actuating the Helmholtz coil as a function of sensor signals, in which at least one first sensor ( 1 ) is arranged outside the predetermined volume in order to produce a signal ( 1 a ) which depends on the magnetic and/or electromagnetic field at the location of the sensor ( 1 ), and at least one second sensor ( 2 ) is arranged inside the predetermined volume, in order to produce a signal ( 2 a ) which depends on the magnetic and/or electromagnetic field at the location of the sensor ( 2 ), and the signals from the first sensor ( 1 a ) and from the second sensor ( 2 a ) are used as the input signals ( 3 a , 3 b ) for actuating a regulator amplifier ( 3 ) associated with the Helmholtz coil.