ASTM A772/A772M-00
(Test Method)Standard Test Method for ac Magnetic Permeability of Materials Using Sinusoidal Current
Standard Test Method for ac Magnetic Permeability of Materials Using Sinusoidal Current
SCOPE
1.1 This test method provides a means for determination of the impedance permeability (µz) of ferromagnetic materials under the condition of sinusoidal current (sinusoidal H) excitation. Test specimens in the form of laminated toroidal cores, tape-wound toroidal cores, and link-type laminated cores having uniform cross sections and closed flux paths (no air gaps) are used. The method is intended as a means for determining the magnetic performance of ferromagnetic strip having a thickness less than or equal to 0.025 in. [0.635 mm].
1.2 This test method shall be used in conjunction with those applicable paragraphs in Practice A34/A34M.
1.3 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.
1.4 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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Standards Content (Sample)
NOTICE: This standard has either been superseded and replaced by a new version or withdrawn. Contact ASTM
International (www.astm.org) for the latest information.
Designation: A 772/A 772M – 00
Standard Test Method for
ac Magnetic Permeability of Materials Using Sinusoidal
Current
This standard is issued under the fixed designationA 772/A 772M; the number immediately following the designation indicates the year
of original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval.
A superscript epsilon (e) indicates an editorial change since the last revision or reapproval.
1. Scope 4. Significance and Use
1.1 This test method provides a means for determination of 4.1 The permeability determined by this method is the
the impedance permeability (µ ) of ferromagnetic materials impedance permeability. Impedance permeability is the ratio of
z
under the condition of sinusoidal current (sinusoidal H) exci- the peak value of flux density (B ) to the assumed peak
max
tation. Test specimens in the form of laminated toroidal cores, magnetic field strength (H ) without regard to phase. As
z
tape-wound toroidal cores, and link-type laminated cores compared to testing under sinusoidal flux (sinusoidal B)
having uniform cross sections and closed flux paths (no air conditions, the permeabilities determined by this method are
gaps) are used. The method is intended as a means for numerically lower since, for a given test signal frequency, the
determining the magnetic performance of ferromagnetic strip rate of flux change (dB/dt) is higher.
having a thickness less than or equal to 0.025 in. [0.635 mm]. 4.2 This test method is suitable for impedance permeability
1.2 This test method shall be used in conjunction with those measurements at very low magnetic inductions at power
applicable paragraphs in Practice A 34/A 34M. frequencies (50 to 60 Hz) to moderate inductions below the
1.3 The values and equations stated in customary (cgs-emu point of maximum permeability of the material (the knee of the
and inch-pound) or SI units are to be regarded separately as magnetization curve) or until there is visible distortion of the
standard. Within this standard, SI units are shown in brackets current waveform.The lower limit is a function of sample area,
except for the sections concerning calculations where there are secondary turns, and the sensitivity of the flux-reading voltme-
separate sections for the respective unit systems. The values ter used.At higher inductions, measurements of flux-generated
stated in each system may not be exact equivalents; therefore, voltages that are appreciably distorted mean that the flux has
each system shall be used independently of the other. Combin- appreciable harmonic frequency components. The upper limit
ing values from the two systems may result in nonconformance is given by the availability of pure sinusoidal current, which is
with this standard. a function of the power source. In addition, a large ratio ($10)
1.4 This standard does not purport to address all of the of the total series resistance of the primary circuit to the
safety concerns, if any, associated with its use. It is the primary coil impedance is required.With proper test apparatus,
responsibility of the user of this standard to establish appro- this test method is suitable for use at frequencies up to 1 MHz.
priate safety and health practices and determine the applica- 4.3 This test method is suitable for design, specification
bility of regulatory limitations prior to use. acceptance, service evaluation, quality control, and research
use.
2. Referenced Documents
5. Apparatus
2.1 ASTM Standards:
A 34/A 34M Practice for Sampling and Procurement Test- 5.1 Thetestcircuit,whichisschematicallyillustratedinFig.
ing of Magnetic Materials 1, shall consist of the following components.
A 340 Terminology of Symbols and Definitions Relating to 5.2 Power Supply—For power frequency (50- or 60-Hz)
Magnetic Testing testing, a suitable power supply consists of two or three series
connected autotransformers of sufficient power rating. This
3. Terminology
will provide a continuously variable current source to excite
3.1 Definitions—The terms and symbols used in this test the test specimen. For testing at other than power frequency, an
method are defined in Terminology A 340.
ac power source consisting of a low distortion sinosoidal signal
generatorandlinearamplifierarerequired.Theuseoffeedback
control of the power amplifier is permitted.
This test method is under the jurisdiction of ASTM Committee A06 on
5.3 Isolation/Stepdown Transformer—The use of a low
Magnetic Properties and is the direct responsibility of SubcommitteeA06.01 onTest
Methods. distortion isolation/stepdown transformer is highly recom-
Current edition approved Oct. 10, 2000. Published January 2001. Originally
mended for operator safety and to eliminate any dc bias current
published as A 772 – 80. Last previous edition A 772/A 772M – 95.
present when using electronic power supplies. A combined
Annual Book of ASTM Standards, Vol 03.04.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.
NOTICE: This standard has either been superseded and replaced by a new version or withdrawn. Contact ASTM
International (www.astm.org) for the latest information.
A 772/A 772M – 00
FIG. 1 Schematic Circuit for Sinusoidal Current Permeability Test
isolation/stepdown transformer can provide greater control
when testing is done at very low magnetizing currents.
5.4 Primary Series Resistor (Z)—A noninductive resistor
having sufficiently high resistance to maintain sinusoidal cur-
rent conditions at the highest magnetizing current and test
FIG. 2 Schematic of Link-Type Lamination
signal frequency of interest. In practice, resistance values of 10
to 100 V are used. If this resistor is used to measure the
magnetizing current, the resistance shall be known to better
distributed primary winding (N ) of insulated wire shall be
than 0.5 % and the resistance shall not increase by more than
applied on top of the secondary winding and be of sufficient
0.5 % at the rated maximum current of the power supply.
diameter to conduct the highest intended magnetizing current
5.5 True RMS Ammeter (A)—A true rms ammeter or a
safelywithoutsignificantheating.Twistedleadsorbiconductor
combination of a noninductive, precision current viewing
cableshallbeusedtoconnectthespecimenwindingstothetest
resistor and true rms voltmeter shall be used to measure the
apparatus.
magnetizingcurrent.Themetershallhaveanaccuracyofbetter
6.2 Calculation of Test Signals—Testing is done either as
than 0.5 % full scale at the test frequency. The current viewing
specified values of flux density (B ) or magnetic field
max
resistor, if used, shall have an accuracy better than 0.5 % and
strength (H ). Before testing, the rms magnetizing currents or
z
shall have sufficient power rating such that the resistance shall
voltages generated in the secondary shall be calculated using
not vary by more than 0.5 % at the rated maximum current of
the equations found in 7.3 and 7.4 or 8.3 and 8.4.
the power supply.
6.3 Demagnetization—After connecting the primary and
5.6 Flux Measuring Voltmeter (V)—The flux shall be deter-
secondary windings to the apparatus, the test specimen shall be
mined from the voltage induced in the secondary winding
demagnetized by applying a magnetizing current sufficiently
using one of the following type of voltmeter:
large to create a magnetic field strength greater than ten times
(1)anaveragerespondingdigitalvoltmetercalibratedtoread
the coercivity of the test specimen. The magnetizing current
rms volts for a sine wave or
then shall be slowly and smoothly reduced to zero to demag-
(2) a true average responding digital voltmeter.
netize the test specimen. The frequency used should be the
The voltmeter shall have input impedance greater than 1 MV,
same as the test frequency.
a full-scale accuracy of better than 0.5 % at the test frequency,
6.4 Measurement—The magnetizing current shall be care-
and a crest factor capability of 3 or greater.
fully increased until the lowest value of either magnetizing
current (if measuring at a specified value of magnetic field
6. Procedure
strength) or flux density (if measuring at a specified value of
6.1 S
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