Precision permeability measurements on straight bars and strips in the region of high permeability

The construction of a yoke apparatus to give magnetizing forces up to H =3000 on straight samples 20 to 25 cm long, and up to H =5000 on samples 8 to 10 cm long, is described. The method of measuring the magnetizing force by means of search coils is used, and an examination is made of its applicability to strip and bar samples mounted in the yoke apparatus. It is found that, below H = 15, large errors result from the leakage taking place along the length of specimen under test. The conditions for satisfactory compensation for this leakage are detemined, and the method is them shown to give good agreement with tests on rings of similar magnetic properties. In Part 2 the effect of stress in the specimen is considered. Stress may be caused by clamping in the case of bars, or by windings on rings or strip samples is found to be the reluctance between the strips. Conditions of testing to obviate both these sources of error are indicated