ASTM A772/A772M-00(2011)
(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. A number in parentheses indicates the year of last reapproval.
A superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
1. Scope A340 Terminology of Symbols and Definitions Relating to
Magnetic Testing
1.1 This test method provides a means for determination of
the impedance permeability (µ ) of ferromagnetic materials
z
3. Terminology
under the condition of sinusoidal current (sinusoidal H) exci-
3.1 Definitions—The terms and symbols used in this test
tation. Test specimens in the form of laminated toroidal cores,
method are defined in Terminology A340.
tape-wound toroidal cores, and link-type laminated cores
having uniform cross sections and closed flux paths (no air
4. Significance and Use
gaps) are used. The method is intended as a means for
4.1 The permeability determined by this method is the
determining the magnetic performance of ferromagnetic strip
impedancepermeability.Impedancepermeabilityistheratioof
having a thickness less than or equal to 0.025 in. [0.635 mm].
the peak value of flux density (B ) to the assumed peak
max
1.2 This test method shall be used in conjunction with those
magnetic field strength (H ) without regard to phase. As
z
applicable paragraphs in Practice A34/A34M.
compared to testing under sinusoidal flux (sinusoidal B)
1.3 The values and equations stated in customary (cgs-emu
conditions, the permeabilities determined by this method are
and inch-pound) or SI units are to be regarded separately as
numerically lower since, for a given test signal frequency, the
standard. Within this standard, SI units are shown in brackets
rate of flux change (dB/dt) is higher.
except for the sections concerning calculations where there are
4.2 This test method is suitable for impedance permeability
separate sections for the respective unit systems. The values
measurements at very low magnetic inductions at power
stated in each system may not be exact equivalents; therefore,
frequencies (50 to 60 Hz) to moderate inductions below the
each system shall be used independently of the other. Combin-
point of maximum permeability of the material (the knee of the
ingvaluesfromthetwosystemsmayresultinnonconformance
magnetization curve) or until there is visible distortion of the
with this standard.
currentwaveform.Thelowerlimitisafunctionofsamplearea,
1.4 This standard does not purport to address all of the
secondary turns, and the sensitivity of the flux-reading voltme-
safety concerns, if any, associated with its use. It is the
ter used.At higher inductions, measurements of flux-generated
responsibility of the user of this standard to establish appro-
voltages that are appreciably distorted mean that the flux has
priate safety and health practices and determine the applica-
appreciable harmonic frequency components. The upper limit
bility of regulatory limitations prior to use.
is given by the availability of pure sinusoidal current, which is
2. Referenced Documents a function of the power source. In addition, a large ratio ($10)
2 of the total series resistance of the primary circuit to the
2.1 ASTM Standards:
primary coil impedance is required.With proper test apparatus,
A34/A34M Practice for Sampling and Procurement Testing
this test method is suitable for use at frequencies up to 1 MHz.
of Magnetic Materials
4.3 This test method is suitable for design, specification
acceptance, service evaluation, quality control, and research
This test method is under the jurisdiction of ASTM Committee A06 on
use.
MagneticPropertiesandisthedirectresponsibilityofSubcommitteeA06.01onTest
Methods.
5. Apparatus
Current edition approved May 1, 2011. Published May 2011. Originally
5.1 Thetestcircuit,whichisschematicallyillustratedinFig.
approved in 1980. Last previous edition approved in 2005 as A772/A772M – 00
(2005). DOI:10.1520/A0772_A0772M-00R11.
1, shall consist of the following components.
For referenced ASTM standards, visit the ASTM website, www.astm.org, or
5.2 Power Supply—For power frequency (50- or 60-Hz)
contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM
testing, a suitable power supply consists of two or three series
Standards volume information, refer to the standard’s Document Summary page on
the ASTM website. connected autotransformers of sufficient power rating. This
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.
A772/A772M–00 (2011)
uniformity of magnetic field strength throughout the specimen,
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)
shall exceed nine times the radial width (w).
FIG. 1 Schematic Circuit for Sinusoidal Current Permeability Test
6.1.2 A secondary winding (N ) using insulated wire shall
be uniformly distributed over the test specimen using a
sufficient number of turns so that a measurable voltage will be
will provide a continuously variable current source to excite
obtained at the lowest flux density of interest. A uniformly
the test specimen. For testing at other than power frequency, an
distributed primary winding (N ) of insulated wire shall be
acpowersourceconsistingofalowdistortionsinosoidalsignal
applied on top of the secondary winding and be of sufficient
generatorandlinearamplifierarerequired.Theuseoffeedback
diameter to conduct the highest intended magnetizing current
control of the power amplifier is permitted.
safelywithoutsignificantheating.Twistedleadsorbiconductor
5.3 Isolation/Stepdown Transformer—The use of a low
cableshallbeusedtoconnectthespecimenwindingstothetest
distortion isolation/stepdown transformer is highly recom-
apparatus.
mended for operator safety and to eliminate any dc bias current
6.2 Calculation of Test Signals—Testing is done either as
present when using electronic power supplies. A combined
specified values of flux density (B ) or magnetic field
max
isolation/stepdown transformer can provide greater control
strength (H ). Before testing, the rms magnetizing currents or
z
when testing is done at very low magnetizing currents.
voltages generated in the secondary shall be calculated using
5.4 Primary Series Resistor (Z)—A noninductive resistor
the equations found in 7.3 and 7.4 or 8.3 and 8.4.
having sufficiently high resistance to maintain sinusoidal cur-
6.3 Demagnetization—After connecting the primary and
rent conditions at the highest magnetizing current and test
secondary windings to the apparatus, the test specimen shall be
signal frequency of interest. In practice, resistance values of 10
demagnetized by applying a magnetizing current sufficiently
to 100 V are used. If this resistor is used to measure the
large to create a magnetic field strength greater than ten times
magnetizing current, the resistance shall be known to better
the coercivity of the test specimen. The magnetizing current
than 0.5 % and the resistance shall not increase by more than
then shall be slowly and smoothly reduced to zero to demag-
0.5 % at the rated maximum current of the power supply.
netize the test specimen. The frequency used should be the
5.5 True RMS Ammeter (A)—A true rms ammeter or a
same as the test frequency.
combination of a noninductive, precision current viewing
6.4 Measurement—The magnetizing current shall be care-
resistor and true rms voltmeter shall be used to measure the
fully increased until the lowest value of either magnetizing
magnetizingcurrent.Themetershallhaveanaccuracyofbetter
current (if measuring at a specified value of magnetic field
than 0.5 % full scale at the test frequency. The current viewing
strength) or flux density (if measuring at a specified value of
resistor, if used, shall have an accuracy better than 0.
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