Instruments and Systems: Monitoring, Control, and Diagnostics Annotation << Back Determination of Magnetic Properties of Ferromagnetic Material Based on Diagnostic Data of the Cylinder Sample Against the Criterion of its Length D.А. SANDULYAK, I.A. SOLOVEV, А.V. SANDULYAK, А.А. SANDULYAK, V.A. ERSHOVA The method of identifi cation of the relative length’ criterion value of the studied ferromagnetic sample λ = [λ] is considered – when the experimentally obtained dependence goes to the automodel region, i.e. to the "plateau", for example, sample’ magnetic induction B in the dependence from λ. In this case, due to vanishing small sample’ demagnetizing factor, the magnetic properties of the studied sample corresponds to the properties for its material. The value [λ] is proposed to be determined using the concept of piecewise linear approximation, adapted to the specifi c (logarithmic) coordinates: the ascending nonlinear section of the resulting λ-dependence of B should be approximated by power dependence that in the logarithmic coordinates maps this section as "linear" (quasilinear). Then the value of λ = [λ] is determined by the abscissa of its intersection point with the interpolated line of the tail automodel section (i.e. by characteral line infl ection point λ-dependence of B). The obtained family of λ-dependencies of B for steel samples (in Russian steel 40Kh) in the range of λ = 1.1... 50 made it possible to establish the criterion values of λ = [λ] and dependence [λ] on the fi eld strength H in the range of H = 5.2... 127 kA/m. It turned out to be decreasing dependence from [λ] = 30 to [λ] = 3.3, obeying the power dependence. According to data B at the λ ≥ [λ] the magnetic permeability μ data of the samples’ material were obtained. Decreasing from μ = 225 to μ = 12.4 (according to the established power dependence), it also allows to fi nd the power μ-dependence of [λ]. Кeywords: ferromagnetic material, relative length of sample, magnetic induction, automodel section, accommodate piecewise approximation. DOI: 10.25791/pribor.11.2023.1450 Pp. 01-9.