ASTM A772/A772M-00(2011)e1
(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
SIGNIFICANCE AND USE
The permeability determined by this method is the impedance permeability. Impedance permeability is the ratio of the peak value of flux density (Bmax) to the assumed peak magnetic field strength (Hz) without regard to phase. As compared to testing under sinusoidal flux (sinusoidal B) conditions, the permeabilities determined by this method are numerically lower since, for a given test signal frequency, the rate of flux change (dB/dt) is higher.
This test method is suitable for impedance permeability measurements at very low magnetic inductions at power frequencies (50 to 60 Hz) to moderate inductions below the point of maximum permeability of the material (the knee of the magnetization curve) or until there is visible distortion of the current waveform. The lower limit is a function of sample area, secondary turns, and the sensitivity of the flux-reading voltmeter used. At higher inductions, measurements of flux-generated voltages that are appreciably distorted mean that the flux has appreciable harmonic frequency components. The upper limit is given by the availability of pure sinusoidal current, which is a function of the power source. In addition, a large ratio (≥10) of the total series resistance of the primary circuit to the primary coil impedance is required. With proper test apparatus, this test method is suitable for use at frequencies up to 1 MHz.
This test method is suitable for design, specification acceptance, service evaluation, quality control, and research use.
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)
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Designation: A772/A772M − 00(Reapproved 2011)
Standard Test Method for
AC Magnetic Permeability of Materials Using Sinusoidal
Current
This standard is issued under the fixed designationA772/A772M; the number immediately following the designation indicates the year
of original adoption or, in the case of revision, the year of last revision.Anumber in parentheses indicates the year of last reapproval.
A superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
ε NOTE—Updated 6.2 and 7.3 editorially in August 2011.
1. Scope of Magnetic Materials
A340Terminology of Symbols and Definitions Relating to
1.1 This test method provides a means for determination of
Magnetic Testing
the impedance permeability (µ ) of ferromagnetic materials
z
under the condition of sinusoidal current (sinusoidal H) exci-
3. Terminology
tation. Test specimens in the form of laminated toroidal cores,
tape-wound toroidal cores, and link-type laminated cores
3.1 Definitions—The terms and symbols used in this test
having uniform cross sections and closed flux paths (no air
method are defined in Terminology A340.
gaps) are used. The method is intended as a means for
determining the magnetic performance of ferromagnetic strip
4. Significance and Use
having a thickness less than or equal to 0.025 in. [0.635 mm].
4.1 The permeability determined by this method is the
1.2 Thistestmethodshallbeusedinconjunctionwiththose
impedancepermeability.Impedancepermeabilityistheratioof
applicable paragraphs in Practice A34/A34M.
the peak value of flux density (B ) to the assumed peak
max
magnetic field strength (H ) without regard to phase. As
1.3 The values and equations stated in customary (cgs-emu z
compared to testing under sinusoidal flux (sinusoidal B)
and inch-pound) or SI units are to be regarded separately as
conditions, the permeabilities determined by this method are
standard. Within this standard, SI units are shown in brackets
numerically lower since, for a given test signal frequency, the
except for the sections concerning calculations where there are
rate of flux change (dB/dt) is higher.
separate sections for the respective unit systems. The values
stated in each system may not be exact equivalents; therefore,
4.2 This test method is suitable for impedance permeability
each system shall be used independently of the other. Combin-
measurements at very low magnetic inductions at power
ingvaluesfromthetwosystemsmayresultinnonconformance
frequencies (50 to 60 Hz) to moderate inductions below the
with this standard.
pointofmaximumpermeabilityofthematerial(thekneeofthe
1.4 This standard does not purport to address all of the magnetization curve) or until there is visible distortion of the
safety concerns, if any, associated with its use. It is the
currentwaveform.Thelowerlimitisafunctionofsamplearea,
responsibility of the user of this standard to establish appro- secondary turns, and the sensitivity of the flux-reading voltme-
priate safety and health practices and determine the applica- ter used.At higher inductions, measurements of flux-generated
bility of regulatory limitations prior to use. voltages that are appreciably distorted mean that the flux has
appreciable harmonic frequency components. The upper limit
2. Referenced Documents
is given by the availability of pure sinusoidal current, which is
a function of the power source. In addition, a large ratio (≥10)
2.1 ASTM Standards:
of the total series resistance of the primary circuit to the
A34/A34MPractice for Sampling and Procurement Testing
primarycoilimpedanceisrequired.Withpropertestapparatus,
this test method is suitable for use at frequencies up to 1 MHz.
This test method is under the jurisdiction of ASTM Committee A06 on
4.3 This test method is suitable for design, specification
MagneticPropertiesandisthedirectresponsibilityofSubcommitteeA06.01onTest
Methods.
acceptance, service evaluation, quality control, and research
Current edition approved May 1, 2011. Published May 2011. Originally
use.
approved in 1980. Last previous edition approved in 2005 as A772/
A772M–00(2005). DOI:10.1520/A0772_A0772M-00R11E01.
5. Apparatus
For referenced ASTM standards, visit the ASTM website, www.astm.org, or
contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM
5.1 Thetestcircuit,whichisschematicallyillustratedinFig.
Standards volume information, refer to the standard’s Document Summary page on
the ASTM website. 1, shall consist of the following components.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
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A772/A772M − 00 (2011)
secondary winding encloses minimal air flux. All test speci-
mens shall have a uniform rectangular cross section.
6.1.1 The cross-sectional area and mean magnetic path
length of the test specimen shall be calculated using the
equations in 7.1 and 7.2 or 8.1 and 8.2. To obtain acceptable
uniformityofmagneticfieldstrengththroughoutthespecimen,
FIG. 1 Schematic Circuit for Sinusoidal Current Permeability Test
the following dimensional constraints shall be observed:
(1) for a toroid the inside diameter to outside diameter ratio
shall exceed 0.82 and
(2) for the link specimen shown in Fig. 2, the separation (s)
5.2 Power Supply—For power frequency (50- or 60-Hz)
shall exceed nine times the radial width (w).
testing, a suitable power supply consists of two or three series
6.1.2 A secondary winding (N ) using insulated wire shall
connected autotransformers of sufficient power rating. This 2
be uniformly distributed over the test specimen using a
will provide a continuously variable current source to excite
sufficient number of turns so that a measurable voltage will be
thetestspecimen.Fortestingatotherthanpowerfrequency,an
obtained at the lowest flux density of interest. A uniformly
acpowersourceconsistingofalowdistortionsinosoidalsignal
distributed primary winding (N ) of insulated wire shall be
generatorandlinearamplifierarerequired.Theuseoffeedback 1
applied on top of the secondary winding and be of sufficient
control of the power amplifier is permitted.
diameter to conduct the highest intended magnetizing current
5.3 Isolation/Stepdown Transformer—The use of a low
safelywithoutsignificantheating.Twistedleadsorbiconductor
distortion isolation/stepdown transformer is highly recom-
cableshallbeusedtoconnectthespecimenwindingstothetest
mendedforoperatorsafetyandtoeliminateanydcbiascurrent
apparatus.
present when using electronic power supplies. A combined
6.2 Calculation of Test Signals—Testing is done either at
isolation/stepdown transformer can provide greater control
specified values of flux density (B ) or magnetic field
when testing is done at very low magnetizing currents. max
strength (H ). Before testing, the rms magnetizing currents or
z
5.4 Primary Series Resistor (Z)—A noninductive resistor
voltages generated in the secondary shall be calculated using
having sufficiently high resistance to maintain sinusoidal cur-
the equations found in 7.3 and 7.4 or 8.3 and 8.4.
rent conditions at the highest magnetizing current and test
6.3 Demagnetization—After connecting the primary and
signalfrequencyofinterest.Inpractice,resistancevaluesof10
secondarywindingstotheapparatus,thetestspecimenshallbe
to 100 Ω are used. If this resistor is used to measure the
demagnetized by applying a magnetizing current sufficiently
magnetizing current, the resistance shall be known to better
large to create a magnetic field strength greater than ten times
than 0.5% and the resistance shall not increase by more than
the coercivity of the test specimen. The magnetizing current
0.5% at the rated maximum current of the power supply.
then shall be slowly and smoothly reduced to zero to demag-
5.5 True RMS Ammeter (A)—A true rms ammeter or a
netize the test specimen. The frequency used should be the
combination of a noninductive, precision current viewing
same as the test frequency.
resistor and true rms voltmeter shall be used to measure the
6.4 Measurement—The magnetizing current shall be care-
magnetizingcurrent.Themetershallhaveanaccuracyofbetter
fully increased until the lowest va
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