ASTM A932/A932M-01(2012)
(Test Method)Standard Test Method for Alternating-Current Magnetic Properties of Amorphous Materials at Power Frequencies Using Wattmeter-Ammeter-Voltmeter Method with Sheet Specimens
Standard Test Method for Alternating-Current Magnetic Properties of Amorphous Materials at Power Frequencies Using Wattmeter-Ammeter-Voltmeter Method with Sheet Specimens
SIGNIFICANCE AND USE
4.1 This test method provides a satisfactory means of determining various ac magnetic properties of amorphous magnetic materials. It was developed to supplement the testing of toroidal and Epstein specimens. For testing toroidal specimens of amorphous materials, refer to Test Method A912/A912M.
4.2 The procedures described herein are suitable for use by manufacturers and users of amorphous magnetic materials for materials specification acceptance and manufacturing control.Note 2—This test method has been principally applied to the magnetic testing of thermally, magnetically annealed, and flattened amorphous strip at 50 and 60 Hz. Specific core loss at 13 or 14 kG [1.3 or 1.4T], specific exciting power at 13 or 14 kG [1.3 or 1.4T], and the flux density, B, at 1 Oe [79.6 A/m] are the recommended parameters for evaluating power grade amorphous materials.
SCOPE
1.1 This test method covers tests for various magnetic properties of flat-cast amorphous magnetic materials at power frequencies (50 and 60 Hz) using sheet-type specimens in a yoke-type test fixture. It provides for testing using either single- or multiple-layer specimens. Note 1—This test method has been applied only at frequencies of 50 and 60 Hz, but with proper instrumentation and application of the principles of testing and calibration embodied in the test method, it is believed to be adaptable to testing at frequencies ranging from 25 to 400 Hz.
1.2 This test method provides a test for specific core loss, specific exciting power and ac peak permeability at moderate and high flux densities, but is restricted to very soft magnetic materials with dc coercivities of 0.07 Oe [5.57 A/m] or less.
1.3 The test method also provides procedures for calculating ac peak permeability from measured peak values of total exciting currents at magnetic field strengths up to about 2 Oe [159 A/m].
1.4 Explanation of symbols and abbreviated definitions appear in the text of this test method. The official symbols and definitions are listed in Terminology A340.
1.5 This test method shall be used in conjunction with Practice A34/A34M.
1.6 The values stated in either 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. 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.
1.7 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: A932/A932M − 01 (Reapproved 2012)
Standard Test Method for
Alternating-Current Magnetic Properties of Amorphous
Materials at Power Frequencies Using Wattmeter-Ammeter-
Voltmeter Method with Sheet Specimens
This standard is issued under the fixed designationA932/A932M; 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.
1. Scope responsibility of the user of this standard to establish appro-
priate safety and health practices and determine the applica-
1.1 This test method covers tests for various magnetic
bility of regulatory limitations prior to use.
properties of flat-cast amorphous magnetic materials at power
frequencies (50 and 60 Hz) using sheet-type specimens in a
2. Referenced Documents
yoke-type test fixture. It provides for testing using either
2.1 ASTM Standards:
single- or multiple-layer specimens.
A34/A34MPractice for Sampling and Procurement Testing
NOTE 1—This test method has been applied only at frequencies of 50
of Magnetic Materials
and 60 Hz, but with proper instrumentation and application of the
A340Terminology of Symbols and Definitions Relating to
principles of testing and calibration embodied in the test method, it is
Magnetic Testing
believed to be adaptable to testing at frequencies ranging from 25 to
A343/A343MTest Method for Alternating-Current Mag-
400Hz.
netic Properties of Materials at Power Frequencies Using
1.2 This test method provides a test for specific core loss,
Wattmeter-Ammeter-Voltmeter Method and 25-cm Ep-
specific exciting power and ac peak permeability at moderate
stein Test Frame
and high flux densities, but is restricted to very soft magnetic
A876Specification for Flat-Rolled, Grain-Oriented, Silicon-
materials with dc coercivities of 0.07 Oe [5.57 A/m] or less.
Iron, Electrical Steel, Fully Processed Types
1.3 Thetestmethodalsoprovidesproceduresforcalculating
A901Specification for Amorphous Magnetic Core Alloys,
ac peak permeability from measured peak values of total
Semi-Processed Types
exciting currents at magnetic field strengths up to about 2 Oe
A912/A912MTest Method for Alternating-Current Mag-
[159 A/m].
netic Properties of Amorphous Materials at Power Fre-
quencies Using Wattmeter-Ammeter-Voltmeter Method
1.4 Explanation of symbols and abbreviated definitions
with Toroidal Specimens
appear in the text of this test method.The official symbols and
definitions are listed in Terminology A340.
3. Terminology
1.5 This test method shall be used in conjunction with
3.1 The definitions of terms, symbols, and conversion fac-
Practice A34/A34M.
tors relating to magnetic testing, used in this test method, are
1.6 The values stated in either customary (cgs-emu and found in Terminology A340.
inch-pound) or SI units are to be regarded separately as
3.2 Definitions of Terms Specific to This Standard:
standard. Within this standard, SI units are shown in brackets.
3.2.1 sheet specimen—arectangularspecimencomprisedof
Thevaluesstatedineachsystemmaynotbeexactequivalents;
a single piece of material or parallel multiple strips of material
therefore,eachsystemshallbeusedindependentlyoftheother.
arranged in a single layer.
Combiningvaluesfromthetwosystemsmayresultinnoncon-
3.2.2 specimen stack—testspecimens(asin3.2.1)arranged
formance with this standard.
in a stack two or more layers high.
1.7 This standard does not purport to address all of the
4. Significance and Use
safety concerns, if any, associated with its use. It is the
4.1 This test method provides a satisfactory means of
determining various ac magnetic properties of amorphous
This test method is under the jurisdiction of ASTM Committee A06 on
MagneticPropertiesandisthedirectresponsibilityofSubcommitteeA06.01onTest
Methods. For referenced ASTM standards, visit the ASTM website, www.astm.org, or
CurrenteditionapprovedMay1,2012.PublishedJuly2012.Originallyapproved contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM
in 1995. Last previous edition approved in 2006 as A932/A932M–01(2006). Standards volume information, refer to the standard’s Document Summary page on
DOI:10.1520/A0932_A0932M-01R12. the ASTM website.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
A932/A932M − 01 (2012)
magneticmaterials.Itwasdevelopedtosupplementthetesting 5.2 Some amorphous magnetic materials are highly magne-
of toroidal and Epstein specimens. For testing toroidal speci- tostrictive. This is an additional potential source of error
mens of amorphous materials, refer to Test Method A912/ because even a small amount of surface loading, twisting, or
A912M. flattening will cause a noticeable change in the measured
values.
4.2 The procedures described herein are suitable for use by
manufacturers and users of amorphous magnetic materials for
6. Basic Test Circuit
materials specification acceptance and manufacturing control.
6.1 Fig. 1 provides a schematic circuit diagram for the test
NOTE 2—This test method has been principally applied to the magnetic
method.Apowersourceofpreciselycontrollableacsinusoidal
testingofthermally,magneticallyannealed,andflattenedamorphousstrip
voltage is used to energize the primary circuit. To minimize
at 50 and 60 Hz. Specific core loss at 13 or 14 kG [1.3 or 1.4T], specific
exciting power at 13 or 14 kG [1.3 or 1.4T], and the flux density, B,at1 flux-waveform distortion, current ratings of the power source
Oe [79.6 A/m] are the recommended parameters for evaluating power
and of the wiring and switches in the primary circuit shall be
grade amorphous materials.
such as to provide very low impedance relative to the imped-
ance arising from the test fixture and test specimen. Ratings of
5. Interferences
switches and wiring in the secondary circuit also shall be such
5.1 Because amorphous magnetic strip is commonly less
astocausenegligiblevoltagedropbetweentheterminalsofthe
than 0.0015 in. [0.04 mm] thick, surface roughness tends to
secondary test winding and the terminals of the measuring
have a large effect on the cross-sectional area and the cross
instruments.
sectioninsomeareascanbelessthanthecomputedaverage.In
suchcases,thetestresultsusingasingle-stripspecimencanbe
7. Apparatus
substantially different from that measured with a stack of
7.1 The test circuit shall incorporate as many of the follow-
several strips. One approach to minimize the error caused by
ing components as are required to perform the desired mea-
surface roughness is to use several strips in a stack to average
surements.
out the variations. The penalty for stacking is that the active
magnetic path length of the specimen stack becomes poorly 7.2 Yoke Test Fixture—Fig.2showsalinedrawingofayoke
fixture. Directions concerning the design, construction, and
defined. The variation of the active length increases with each
additional strip in the stack. Moreover, the active length for calibration of the fixture are given in 7.2.1, 7.2.2, Annex A1,
stacked strips tends to vary from sample to sample. As the Annex A2, and Annex A3.
stack height increases, the error as a result of cross-sectional 7.2.1 Yoke Structure—Various dimensions and fabrication
variations diminishes but that as a result of length variations procedures in construction are permissible. Since the recom-
increases with the overall optimum at about four to six layers. mended calibration procedure requires correlation with the
The accuracy for stacked strips is never as good as for a single 25-cm Epstein test, the minimum inside dimension between
layer of smooth strip. pole faces must be at least 22 cm [220 mm]. The thickness of
FIG. 1 Basic Block Circuit Diagram of the Wattmeter Method
A932/A932M − 01 (2012)
Use of a digital flux voltmeter with high input impedance
(typically, 10 MΩ) is recommended to minimize loading
effects and to reduce instrument loss compensation. If an
analog flux voltmeter is used, its input resistance shall be
greaterthen10000Ω/Voffull-scaleindication.Voltageranges
and number of significant digits shall be consistent with the
accuracy specified above. Care shall be taken to avoid errors
caused by temperature and frequency effects in the instrument.
NOTE3—Inaccuraciesinsettingthetestvoltageproduceerrorsapproxi-
mately two times as large in the specific core loss.
7.5 RMS Voltmeter, V —A true rms-indicating voltmeter
rms
FIG. 2 Single-Yoke Fixture (Exploded View)
shall be provided for evaluating the form factor of the voltage
induced in the secondary winding of the test fixture and for
evaluating the instrument losses. The accuracy of the rms
the pole faces should be not less than 2.5 cm [25 mm]. To
voltmeter shall be the same as specified for the flux voltmeter.
minimize the influences of coil-end and pole-face effects, the
Either digital or analog rms voltmeters are permitted. The
yokes should be thicker than the recommended minimum. For
normally high input impedance of digital rms voltmeters is
calibrationpurposes,itissuggestedthatthewidthofthefixture
desirable to minimize loading effects and to reduce the mag-
be at least 12.0 cm [120 mm] which corresponds to the
nitude of instrument loss compensations. The input resistance
combined width of four Epstein-type specimens.
of an analog rms voltmeter shall not be less than 10000 Ω/V
7.2.2 Test Windings—The test windings, which shall consist
of full-scale indication.
of a primary (exciting) winding and a secondary (potential)
winding, shall be uniformly and closely wound on a
7.6 Wattmeter, W—The full-scale accuracy of the wattmeter
nonmagnetic, nonconducting coil form and each shall span the
shall not be lower than 0.25% at the test frequency and unity
greatest possible distance between the pole faces of the yoke
power factor. The power factor encountered by a wattmeter
fixture. It is recommended that the number of turns in the
during a core loss test on a specimen is always less than unity
primaryandsecondarywindingsbeequal.Thenumberofturns
and, at flux densities far above the knee of the magnetization
may be chosen to suit the instrumentation, mass of specimen,
curve, approaches zero. The wattmeter must maintain 1.0%
and test frequency. The secondary winding shall be the
accuracy at the lowest power factor which is presented to it.
innermost winding. The primary and secondary turns shall be
Variablescalingdevicesmaybeusedtocausethewattmeterto
wound in the same direction from a common starting point at
indicatedirectlyinunitsofspecificcorelossifthecombination
one end of the coil form.Also, to minimize self-impedances of
of basic instruments and scaling devices conforms to the
thewindings,theopeninginthecoilformshouldbenogreater
specifications stated here.
than that required to allow easy insertion of the test specimen.
7.6.1 Electronic Digital Wattmeter—An electronic digital
Construction and mounting of the test coil assembly must be
wattmeter is preferred in this test method because of its digital
such that the test specimen will be maintained without me-
readout and its capability for direct interfacing with electronic
chanical distortion in the plane established by the pole faces of
the yoke(s) of the test fixture. data acquisition systems. A combination true rms voltmeter-
wattmeter-rms ammeter is acceptable to reduce the number of
7.3 Air-Flux Compensator—To provide a means of deter-
instruments connected in the test circuit.
mining intrinsic flux density in the test specimen, an air-core
7.6.1.1 The voltage input circuitry of the electronic digital
mutual inductor shall constitute part of the test-coil system.
wattmeter must have an input impedance sufficiently high so
The respective primary and secondary windings of the air-core
inductorandthetest-specimencoilshallbeconnectedinseries that connection to the secondary winding of the test fixture
during testing does not change the terminal voltage of the
andthevoltagepolaritiesofthesecondarywindingsshallbein
opposition. By proper adjustment of the mutual inductance of secondary by more than 0.05%. Also, the voltage input
the air-core inductor, the average voltage developed across the circuitry must be capable of accepting the maximum peak
combined secondary windings is proportional to the intrinsic
voltage which is induced in the secondary winding during
flux density in the test specimen. Directions for construction testing.
and adjustment of the air-core mutual inductor for air flux are
7.6.1.2 The current input circuitry of the electronic digital
found in Annex A3.
wattmeter should have as low an input impedance as possible,
7.4 Flux Voltmeter, V—A full-wave, true average respond- preferably no more than 0.1 Ω, otherwise the flux waveform
f
distortion tends to be excessive. The effect of moderate
ing voltmeter, with scale readings in average volts times π
waveform distortion is addressed in 10.3. The current input
=
. 2/4 so that its indications will be identical with those of a
circuitry must be capable of accepting the maximum rms
true rms voltmeter on a pure sinusoidal voltage, shall be
current and the maximum peak current drawn by the primary
provided for evaluating the peak value of the test flux density.
To produce the estimated precision of test under this test winding of the test transformer when core loss tests are being
performed. In particular, since the primary current will be very
method, the full-scale meter errors shall not exceed 0.25%
(Note3).Eitherdigitaloranalogfluxvoltmetersarepermitted. nonsinusoidal (peaked) if core loss tests are performed on a
A932/A932M − 01 (2012)
specimen at flux densities above the knee of the magnetization and be able to accommodate voltage with a crest factor of 5 or
curve, the crest factor capability of the current input circuitry more.Caremustbeexercisedthatthestandardresistor(usually
should be 5 or more. in the range 0.1 to 1.0 Ω) carrying the exciting current has
7.6.2 Electrodynamometer Wattmeter—Areflecting-typeas- adequate current-carrying capacity and is accurate to at least
tatic electrodynamometer wattmeter is permitted as an alterna- 0.1%. It shall have negligible variation with temperature and
tive to an electronic wattmeter. frequency under the conditions applicable to this test method.
If desired, the value of the resistor may be such that the
7.6.2.1 The sensitivity of the electrodynamometer wattme-
ter must be such that the connection of the potential circuit of peak-reading voltmeter indicates directly in terms of peak
magnetic field strength, provided that the resis
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