On the problem of the field detection for single sheet testers

Abstract

For single-sheet testers, the field is derived either from the magnetization current or by means of a tangential field coil. The current method, proposed for IEC standardization, is characterized by simple apparatus and good reproducibility but suffers from questionable accuracy due to the lack of correspondence between field and current. The H-coil method exhibits a clear physical basis, but it is criticized for instabilities and many sources of error (specific electronic apparatus each as H-amplifier, B-integrator, and multiplier). The aim of work was to overcome these criticisms and to study possibilities of simplifications of this technique. Instead of electronic integration, a stable phase-accurate RC arrangement is applied. A solid H-coil of high turn area and sufficient areal averaging allows one to dispense with the usual H-amplifier. Instead of using two H-coils for checks of local field variations, a lift apparatus is proposed. Effects of minute-multiplier phase errors can be corrected by means of channel exchange. Results of measurement are presented for stress-coated SiFe and for consolidated amorphous material. These results indicate that with the applied single yoke, sample overhangs must be avoided. For the determination of physically precise loss values, the use of a double yoke in connection with a long H-coil is recommended. It is assumed that a reliable H-coil method will be needed, especially for novel types of materials with lowest loss and high permeability.