Standard Historical Last Updated: Jun 10, 2021
ASTM A348/A348M-05(2015)

Standard Test Method for Alternating Current Magnetic Properties of Materials Using the Wattmeter-Ammeter-Voltmeter Method, 100 to 10 000 Hz and 25-cm Epstein Frame

Significance and Use

4.1 This test method evaluates the performance of flat-rolled magnetic materials over a wide frequency range of ac excitation with and without incremental dc bias, as used on transformers, motors, and other laminated core devices.

4.2 This test method is suitable for design, specification acceptance, service evaluation, and research.

4.3 The application of test results obtained with this test method to the design or evaluation of a particular magnetic device must recognize the influence of the magnetic circuitry upon its performance. Some specific items to consider are size, shape, holes, welding, staking, bolting, bracketing, shorting between laminations, ac waveform, adjacent magnetic fields, and stress.


1.1 This test method covers the determination of the magnetic properties of flat-rolled magnetic materials using Epstein test specimens with double-lap joints in the 25-cm Epstein frame. It covers determination of core loss, rms and peak exciting current, exciting power, magnetic field strength, and permeability. This test method is commonly used to test grain-oriented and nonoriented electrical steels but may also be used to test nickel-iron, cobalt-iron, and other flat-rolled magnetic materials.

1.2 This test method shall be used in conjunction with Practice A34/A34M and Test Method A343/A343M.

1.3 Tests under this test method may be conducted with either normal ac magnetization or with ac magnetization and superimposed dc bias (incremental magnetization).

1.4 In general, this test method has the following limitations:

1.4.1 Frequency—The range of this test method normally covers frequencies from 100 to 10 000 Hz. With proper equipment, the test method may be extended above 10 000 Hz. When tests are limited to the use of power sources having frequencies below 100 Hz, they shall use the procedures of Test Method A343/A343M.

1.4.2 Magnetic Flux Density  (may also be referred to as Flux Density)—The range of magnetic flux density for this test method is governed by the test specimen properties and by the available instruments and other equipment components. Normally, for many materials, the magnetic flux density range is from 1 to 15 kG [0.1 to 1.5 T].

1.4.3 Core Loss and Exciting Power—These measurements are normally limited to test conditions that do not cause a test specimen temperature rise in excess of 50°C or exceed 100 W/lb [220 W/kg].

1.4.4 Excitation—Either rms or peak values of exciting current may be measured at any test point that does not exceed the equipment limitations provided that the impedance of the ammeter shunt is low and its insertion into the test circuit does not cause appreciably increased voltage waveform distortion at the test magnetic flux density.

1.4.5 Incremental Properties—Measurement of incremental properties shall be limited to combinations of ac and dc excitations that do not cause secondary voltage waveform distortion, as determined by the form factor method, to exceed a shift of 10 % away from sine wave conditions.

1.5 The values and equations stated in customary (cgs-emu and inch-pound) or SI units are to be regarded separately as standard. Within this standard, SI units are shown in brackets except for the sections concerning calculations where there are separate sections for the respective unit systems. The values stated in each system may not be exact equivalents; therefore, each system shall be used independently of the other. Combining values from the two systems may result in nonconformance with this standard.

1.6 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use.

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Book of Standards Volume: 03.07
Developed by Subcommittee: A06.01
Pages: 11
DOI: 10.1520/A0348_A0348M-05R15
ICS Code: 29.030