Abstract :
The paper describes an instrument which enables a measurement to be made of power losses, due to eddy currents and hysteresis, that occur in small areas of electrical sheet steel when it is placed in an alternating magnetic field. The measurement, which is nondestructive in that it can be made on a complete sheet without test samples having to be taken, enables both comparative and absolute measurements to be carried out. Illustrations of each are given. The first form of the instrument enabled the principle of the method of measurement to be established and showed that the power-loss properties of sheet steel can vary considerably, even over small areas; the limitation of this early instrument is, in fact, set by the heterogeneity of the steel, which makes it difficult to assign a representative value to a given area. A method of overcoming this limitation is described, and the way in which the instrument might be used to investigate the local variation of permeability is discussed.
