The use of a miniature Lloyd-Fisher square for power-loss measurements at audio frequencies

The paper stresses the need for the development of a standardized commercial method of iron loss measurement at audio frequencies. To assist such a development, the use of a miniaturereproduction of the standard Lloyd-Fisher square is investigated. In comparing results obtained onthe miniature square with those obtained on the standard square, it is found that the hardening effect near the edges of the material due to cutting, is increased and may amount to 5% on the totalloss. Nevertheless, results obtained on the miniature square are probably more representative of values obtained in the practical utilization of sheet metal at audio frequencies. Since the proportionate mass of the overlapping portion in the magnetic square is quite appreciable, its effect is considered in some detail. It is shown that the relation given in B.S. 601:1935, between the loss per unit mass and the total loss measured on the standard square at power frequencies, is applicable to the miniature square at power and higher frequencies. A comparison of loss and permeability measurements on the miniature-square and ring samples demonstrates that the problem of satisfactory sampling becomes more important when test results are required at the low inductions associated with higher-frequency operation.