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R. Grössinger:
"SURVEY OF PULSE FIELD MEASUREMENT TECHNIQUE ";
Vortrag: 2DM Tagung, Lüdenscheid, Deutschland (eingeladen); 16.09.2002 - 17.09.2002.

The characterisation of modern permanent magnet materials like SmCo based or Nd-Fe-B type material is difficult because coercivities up to 5T are possible. The measurement in an Fe-yoke allows fields up to 1.5T which is not sufficient to obtain a full second quadrant demagnetization curve. Additionally the sample needs two plan and parallel surfaces. In magnet laboratories are sometimes vibrating sample magnetometers available which uses a superconducting magnet with fields up to 8T and even more. These magnetometers needs for a hysteresis loop minutes ? this time is given by the allowed rise time dH/dt of the magnet. Additionally these systems operate in a magnetic open circuit, which needs a careful correction of the demagnetizing field. Generally the fast measurement of large industrial shaped samples is an open problem.
Recently the use of pulsed field magnetometers (PFM) for characterising permanent magnets in industrial surroundings where discussed [1,2]. The advantage of a PFM is that a fast loop measurement (within seconds) of magnet samples is possible. A PFM can be calibrated with an absolute accuracy of ±1.5 % [3]. Generally there are two problems applying a transient field pulse on a permanent magnet material:
i) Eddy currents ? the eddy current error scales with dH/dt, the specific resistivity of the material and r2 (r...mean dimension perpendicular to the field). For metallic sintered magnets with dimensions up to 20 mm the eddy current error is usually below 1% [4].
ii) Magnetic viscosity - this effect depends on the actual domain structure and the magnetisation process. It scales with the coercivity however a general scaling law is unknown. For ferrites this error is small. For Sm-Co or Nd-Fe-B type material this error has to be checked for each type of material.
The reliability of PFM measurements on industrial permanent magnets will be shown.