BS EN IEC 60404‑7:2020 pdf download -Magnetic materials Part 7: Method of measurement of the coercivity (up to 160 kA/m) of magnetic materials in an open magnetic circuit.
1 Scope This part of IEC 60404 specifies a method of measurement of the coercivity of magnetic materials in an open magnetic circuit. This document is applicable to all magnetic materials with coercivities from 0,2 A/m to 1 60 kA/m. NOTE Examples of magnetic materials covered by this document are amorphous alloys, nanocrystalline alloys, all softmagnetic crystalline materials (e.g. Fe, FeSi-, CoFe- and FeNi-alloys), soft ferrites, hard metals, semi-hard magnetic alloys (e.g. FeCoTiAl-, FeCoV-, FeCrCo- and AlNiCo-alloys) [1 ] 1 . Special precautions are to be taken in measuring coercivities below 40 A/m, in materials with high conductivity and in test specimens which have a shape different from ellipsoids (see Annex A). 2 Normative references The following documents are referred to in the text in such a way that some or all of their content constitutes requirements of this document. For dated references, only the edition cited applies. For undated references, the latest edition of the referenced document (including any amendments) applies. There are no normative references in this document. 3 Terms and definitions For the purpose of this document, the following terms and definitions apply. ISO and IEC maintain terminological databases for use in standardization at the following addresses: • IEC Electropedia: available at http://www.electropedia.org/ • ISO Online browsing platform: available at http://www.iso.org/obp
4 Principle of the method If a magnetic test specimen is placed in a uniform and unidirectional magnetic field then it will distort this magnetic field unless a condition that no flux (additional to that previously carried by the air space it now occupies) enters or emerges from the test specimen. This condition represents a state of complete demagnetization which occurs when a demagnetizing coercive magnetic field strength is applied to the test specimen such that the magnetic polarization is zero [2]. The test specimen is magnetized to saturation (J s ) and then the magnetic field is reduced smoothly without interruption to zero (J r ). Afterwards the polarity of the magnetic field is reversed and a demagnetizing field is increased until the magnetic polarization of the test specimen is zero. The applied magnetic field strength required to achieve this condition is measured and defined as the coercivity H cJ of the test specimen (see Figure 1 ). A magnetic flux sensing probe enables the detection of the condition of no distortion of a uniform magnetic field by the test specimen and provides the means for determining the coercivity. For this measurement, the test specimen and the magnetic flux sensing probes are placed in an open magnetic circuit in the uniform and unidirectional magnetic field of a solenoid. The flux sensing probe should be placed as follows: a) inside the solenoid, close to the end of the test specimen (Method A – Hall probe, see Figure 3), or b) inside the solenoid, at a distance from the test specimen, depending on the size and permeability of the test specimen (Method A – differential fluxgate probe, see Figure 4), or c) outside the solenoid (Method B – differential fluxgate probe, see Figure 5). The solenoid and measuring equipment shall be connected as shown in Figure 2.
5 Test specimen The shape and the dimensions of the test specimen may be varied provided that they meet the following conditions: a) the test specimen can be placed inside the solenoid so that its major axis is coincident with the axis of the solenoid; b) the test specimen can be magnetized to saturation. NOTE For the effects of shape and non-uniform magnetic properties of the test specimen refer to 9.2.2 and 9.3. 6 Solenoid The magnetic field in the solenoid shall have the following specifications: a) the magnetic field strength in the solenoid over the volume of the test specimen shall not vary by more than ±0,5 %; b) an AC ripple of the magnetic field strength in the solenoid shall be less than ±0,5 % of the magnetic field strength. 7 Compensation for the earth’s magnetic field and static and dynamic magnetic noise fields The measurement of the coercivity of a test specimen of soft magnetic material can be distorted by the earth’s magnetic field and by external static and dynamic magnetic noise fields. Compensation for these can be achieved either by: a) a suitable compensation system for the earth’s magnetic field [4] or a magnetic shield placed around the measurement region, or b) the magnetic flux sensing probe for the measurement of the stray magnetic field of the test specimen is a differential fluxgate probe to suppress an influence of these uniform external magnetic fields (see Figures 4 and 5).