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DKE German Commission for Electrical, Electronic & Information Technologies of DIN and VDE

Overview

The determination of the relative magnetic permeability of feebly magnetic materials is often required to assess their effect on the ambient magnetic field. Typical feebly magnetic materials are austenitic stainless steels and "non-magnetic" brass. The relative magnetic permeability of some of these materials can vary significantly with the applied magnetic field strength. In the majority of cases, these materials find application in the ambient earth's magnetic field. This field in Europe is 35 A/m to 40 A/m, in the Far East, it is 25 A/m to 35 A/m and in North America, it is 25 A/m to 35 A/m. However, at present, methods of measurement are not available to determine the relative magnetic permeability of feebly magnetic materials at such a low value of magnetic field strength. Studies of the properties of feebly magnetic materials have been carried out, primarily with a view to the production of improved reference materials. These studies have shown that it is possible to produce reference materials which have a substantially constant relative magnetic permeability over the range from the earth's magnetic field to at least a magnetic field strength of 100 kA/m. Conventional metallic materials can also be used as reference materials. Their relative magnetic permeability can be determined using the reference method. It is important that the magnetic field strength used during the determination of the relative magnetic permeability is stated for all materials but in particular for conventional materials since the changes with applied magnetic field can be large. This behaviour shall also be considered when using reference materials made from conventional materials to calibrate comparator methods. This is because these methods use magnetic fields that vary through the volume of the material being tested. This makes it difficult to know the relative magnetic permeability to use for the calibration. Where the effect of a feebly magnetic material on the ambient earth's magnetic field is critical, the direct measurement of this effect using a sensitive magnetometer should be considered. This standard specifies a solenoid method, a magnetic moment method, a magnetic balance method and a permeability meter method for the determination of the relative magnetic permeability of feebly magnetic materials (including austenitic stainless steel). The magnetic balance and permeability meter methods are both comparison methods calibrated using reference materials to determine the value of the relative magnetic permeability of the test specimen. The relative magnetic permeability range for each of these methods is shown in Table 1. The methods given are for applied magnetic field strengths of between 5 kA/m and 100 kA/m. The solenoid method is the reference method. The magnetic moment method described is used mainly for the measurement of the relative magnetic permeability of mass standards. Two comparator methods used by industry are described. These can be calibrated using reference materials for which the relative magnetic permeability has been determined using the reference method. When suitable, the magnetic moment method can also be used. The dimensions of the reference material need to be given careful consideration when determining the uncertainty in the calibration value due to self-demagnetization effects. The responsible committee is DKE/K 171 "Magnetische Legierungen und Stahl" ("Magnetic alloys and steels") of the DKE (German Commission for Electrical, Electronic and Information Technologies) at DIN and VDE.

Document: references other documents

Responsible national committee

DKE/K 171 - Magnetische Legierungen und Stahl