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Introduction The models of magnetic devices having a magnetic core without known parameters require the core evaluation by means of sophisticated measurement procedures and systems. For certain models, higher measurement accuracy is of key importance. For the other models, additional factors (speed, cost, measurement instruments and apparatus) may strongly limit achievement of the specific measurement requirements. Numerous techniques have been developed for hysteresis description, among which the models of Preisach, Jiles-Atherton and Stoner-Wolfarth are the most widespread. The existing hysteresis models can be roughly divided in two different classes: mathematical and physical models. Physical models, such as the model of Jiles-Atherton [1], consider the underlying physics of hysteresis to model the phenomenon. Mathematical models, such as the Preisach model [2], consider hysteresis as a superposition of elementary rectangular hysteresis loops. By measuring the Everett-function, a certain weight is assigned to every dipole. Sophisticated Preisach models also comprise dynamical effects and anisotropy. The Stoner-Wolfarth model regards the hysteresis loop as a superposition of an infinite number of dipoles. Here, the dipoles themselves can have a non-rectangular hysteresis loops, and that is why this model has a lot of numerical disadvantages when compared to the Preisach model. The Jiles-Atherton model is the model of choice for the modeling of ferromagnetism in soft magnetic materials, such as electrical steel. Although it was developed over the course of several publications, the classic paper is generally considered to be [1]. David Jiles later published an entire text on magnetism [3], which contains the model, as well as extensions such as stress effects. PSpice software currently includes non-linear magnetic cores based on the Jiles-Atherton model [4]. The Jiles-Atherton model requires both geometric parameters (such as effective air-gap length) and materials parameters (such as domain anisotropy). The required information is simply not available except for a limited number of cores in the supplied library. Vendor data sheet don’t include values for domain anisotropy. Even a relatively innocuous sounding parameter like effective air gap length is fraught with dangerous complications. This paper presents a method and the experimental measurement system for the determination of Jiles-Atherton parameters of the unknown magnetic core by minimizing the error between experimental and simulated magnetic field curves. Comparison of experimental and simulated results validates the procedure. The Jiles-Atherton Parameters The Jiles-Atherton method derives a hysteresis loop out of the Weiss-theory for ferromagnetism. The model relies upon a set of differential equations, for which five parameters have to be determined by a measurement of the hysteresis loop. Jiles and Atherton (1983) used an energy balance to model magnetic hysteresis. The energy supplied to the material by a change in the applied field can be dissipated either as a change in magnetostatic energy, or as hysteresis loss. In the absence of hysteresis, all the energy supplied would go toward modifying the magnetostatic energy. In such a case, the magnetisation would be a reversible, single-valued function of the applied field. This anhysteretic magnetisation an M can be modeled as:   e S an H f M M   (1)