Calibration of magnetic field coil standards by means of field profile measurement

In order to calibrate field coil standards a new setup has been developed by which the field profile of field coils is recorded. From the profile the centre field strength can be related to the SI units of electrical current and length. The main components of the apparatus are a modified, commercially available fluxgate magnetometer, an optical length measuring device, and a motor driven positioning system which moves the fluxgate sensor along the axis of the coil under test. Depending on size and type of the coil a relative uncertainty of some parts in 10 ^{-5} is achievable. Recording the flux profile provides additional information about the device under test, even if its centre field value has been determined by means of Nuclear Magnetic Resonance using protons in pure water, which must be regarded at present as the most accurate method for magnetic field calibration.