GB/Z 28865-2012Specification for anti-EMI soft ferrite materials (English PDF)

Foreword

GB/Z 28865-2012 was issued on 5 November 2012 by the General Administration of Quality Supervision, Inspection and Quarantine and the Standardization Administration of the People's Republic of China, and has been in force since 15 February 2013.

The document is a national standardization guiding technical document - a GB/Z - which gives guidance rather than binding requirements.

1 Scope

China's guiding technical document for the soft ferrite materials used to suppress electromagnetic interference - the material of the ferrite bead moulded round a cable and of the clamp on a monitor lead. A ferrite suppressor is unusual among electronic components in that its job is to be lossy: it does not filter the unwanted high-frequency current so much as absorb it and turn it into heat, and the property that matters is therefore not a clean inductance but the impedance the material presents over a band of frequencies. Which material to choose is a direct trade-off. A high initial permeability gives a large impedance but only up to a modest frequency; a low permeability holds its impedance far higher up the spectrum. Choose wrongly and the bead does nothing at the frequency that is actually causing the trouble. This document classifies the materials, sets out how a grade designation is built, and gives the typical magnetic properties of the main grades - initial permeability, the frequency at which the nominal impedance is measured, that impedance, the saturation flux density, the Curie temperature and the resistivity - together with the test methods. It applies to anti-EMI soft ferrite materials. Being a GB/Z, it is a guiding technical document rather than a compulsory standard.

This guiding technical document specifies the classification, the material grade designations, the main magnetic properties and the test methods for anti-EMI soft ferrite materials.

This guiding technical document applies to anti-EMI soft ferrite materials.

2 Normative references

The following documents are indispensable for the application of this document. For dated references, only the edition cited applies. For undated references, the latest edition of the referenced document, including all amendments, applies.

GB/T 2421.1-2008 Environmental testing for electric and electronic products - General and guidance.

GB/T 2900.60-2002 Electrotechnical terminology - Electromagnetism.

GB/T 9637-2001 Electrotechnical terminology - Magnetic materials and components.

GB/Z 28870-2012 Measuring methods for anti-EMI soft ferrite materials.

3 Definitions

The terms and definitions given in GB/T 2900.60-2002 and GB/T 9637-2001 and the following apply to this document.

3.1 normalized impedance - the product of the single-turn impedance of a bead of specified dimensions, measured under the specified test conditions, and the core constant.

3.2 saturation flux density - the flux density when the maximum value of the magnetic field strength is able to magnetise the material to saturation.

3.3 Curie temperature - the critical temperature at which a ferromagnetic or ferrimagnetic material changes from the ferromagnetic or ferrimagnetic state to the paramagnetic state.

5 Requirements

The typical magnetic properties of the principal anti-EMI soft ferrite materials shall comply with Tables 1 and 2 respectively. Table 1 covers the KN class of NiZn and NiCuZn ferrite materials, listing for each grade the initial permeability with its tolerance, the frequency at which the nominal impedance is measured, the nominal impedance, the saturation flux density, the Curie temperature and the resistivity; the grades run from the highest permeability, usable only to a low frequency, down to the lowest, usable to a much higher one. A note records that manufacturers may supply materials of other supplementary grades. The footnotes fix the measurement conditions: the test temperature, the frequency associated with the initial permeability, the bead size on which the nominal impedance is measured, and the applied field strength at which the saturation flux density is determined.