Maintenance and dissemination of the magnetic field unit at PTB

The different methods which are used at Physikalisch Technische Bundesansta lt (PTB) to disseminate the unit of flux density are presented and compared with respect to their uncertainties, ii de flux density range from 10 muT to 2 T is covered with the lo,vest relative uncertainty of 10(-6) at fields of 1 mT to Z mT, In case of sc fields, field coils are used as standards, the frequency response of which is checked by means of a simple but very re liable inductive measuring technique, A relative uncertainty of 3 10(-3) or even less is typically achieved for frequencies below 30 kHz.