ASTM A932/A932M-95

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Designation: A 932/A932M – 95 An American National Standard
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 designation A 932/A932M; 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 2. Referenced Documents
1.1 This test method covers tests for various magnetic 2.1 ASTM Standards:
properties of flat-cast amorphous magnetic materials at power A 34 Practice for Procurement, Testing and Sampling of
frequencies (50 and 60 Hz) using sheet type specimens in a Magnetic Materials
yoke type test fixture. It provides for testing using either single A 340 Terminology of Symbols and Definitions Relating to
or multiple layer specimens. Magnetic Testing
A 343 Test Method for Alternating-Current Magnetic Prop-
NOTE 1—This test method has been applied only at frequencies of 50
erties of Materials at Power Frequencies Using Wattmeter-
and 60 Hz, but with proper instrumentation and application of the
Ammeter-Voltmeter Method and 25-cm Epstein Frame
principles of testing and calibration embodied in the test method, it is
A 804/A804M Test Methods for Alternating-Current Mag-
believed to be adaptable to testing at frequencies ranging from 25 to 400
Hz.
netic Properties of Materials at Power Frequencies Using
Sheet-Type Test Specimens
1.2 This test method provides a test for specific core loss,
A 876 Specification for Flat-Rolled, Grain-Oriented,
specific exciting power and ac peak permeability at moderate
Silicon-Iron, Electrical Steel, Fully Processed Types
and high flux densities, but is restricted to very soft magnetic
A 876M Specification for Flat-Rolled, Grain-Oriented,
materials with dc coercivities of 0.07 Oe [5.57 A/m] or less.
Silicon-Iron, Electrical Steel, Fully Processed Types (Met-
1.3 The test method also provides procedures for calculating
ric)
ac peak permeability from measured peak values of total
A 901 Specification for Amorphous Magnetic Core Alloys,
exciting currents at magnetic field strengths up to about 2 Oe
Semi-Processed Types
[159 A/m].
A 912 Test Method for Alternating-Current Magnetic Prop-
1.4 Explanation of symbols and abbreviated definitions
erties of Amorphous Materials at Power Frequencies Using
appear in the text of this test method. The official symbols and
Wattmeter-Ammeter-Voltmeter Methods with Toroidal
definitions are listed in Terminology A 340.
Specimens
1.5 This test method shall be used in conjunction with
C 693 Test Method for Density of Glass by Buoyancy
Practice A 34.
1.6 The values stated in either customary units (practical cgs
3. Terminology
& inch-pound) or SI units are to be regarded separately as
3.1 The definitions of terms, symbols, and conversion fac-
standard. Separate derivations are included for each of the unit
tors relating to magnetic testing, used in this test method, are
systems. However, within the general text, SI units are shown
found in Terminology A 340.
in brackets. The values stated in each system are not exact
3.2 Definitions of Terms Specific to This Standard:
equivalents: therefore, each system shall be used independently
3.2.1 sheet specimen—a rectangular specimen comprised
of the other. Combining values from the two systems may
of a single piece of material or parallel multiple strips of
result in nonconformance with the test method.
material arranged in a single layer.
1.7 This standard does not purport to address all of the
3.2.2 specimen stack—test specimens (as in 3.2.1) arranged
safety concerns, if any, associated with its use. It is the
in a stack two or more layers high.
responsibility of the user of this standard to establish appro-
priate safety and health practices and determine the applica-
4. Significance and Use
bility of regulatory limitations prior to 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
This test method is under the jurisdiction of ASTM Committee A-6 on
Magnetic Properties and is the direct responsibility of Subcommittee A06.01 on Test
Methods. Annual Book of ASTM Standards, Vol 03.04.
Current edition approved Nov. 10, 1995. Published January 1996. Annual Book of ASTM Standards, Vol 15.02.
Copyright © ASTM, 100 Barr Harbor Drive, West Conshohocken, PA 19428-2959, United States.
A 932/A932M
of toroidal and Epstein specimens. For testing toroidal speci- because even a small amount of surface loading, twisting or
mens of amorphous materials, refer to Test Method A 912. flattening will cause a noticeable change in the measured
4.2 The procedures described herein are suitable for use by values.
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. A power source of precisely controllable ac sinusoidal
testing of thermally, magnetically annealed and flattened amorphous strip
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
flux-waveform distortion, current ratings of the power source
exciting power at 13 or 14 kG [1.3 or 1.4T], and the flux density, B, at 1
and of the wiring and switches in the primary circuit shall be
Oe [79.6 A/m] are the recommended parameters for evaluating power
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
as to cause negligible voltage drop between the terminals of the
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.
section in some areas can be less than the computed average. In
7. Apparatus
such cases the test results using a single strip specimen can be
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 due to 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 7.2 Yoke Test Fixture—Fig. 2 shows a line drawing of a
magnetic path length of the specimen stack becomes poorly
yoke fixture. Directions concerning the design, construction,
defined. The variation of the active length increases with each and calibration of the fixture are given in 7.2.1, 7.2.2, Annex
additional strip in the stack. Moreover, the active length for A1, Annex A2, and Annex A3.
stacked strips tends to vary from sample to sample. As the 7.2.1 Yoke Structure—Various dimensions and fabrication
stack height increases, the error due to cross-sectional varia- procedures in construction are permissible. Since the recom-
tions diminishes but that due to length variations increases with mended calibration procedure requires correlation with the
the overall optimum at about four to six layers. The accuracy 25-cm Epstein test, the minimum inside dimension between
for stacked strips is never as good as for a single layer of pole faces must be at least 22 cm [220 mm]. The thickness of
smooth strip. the pole faces should be not less than 2.5 cm [25 mm]. To
5.2 Some amorphous magnetic materials are highly magne- minimize the influences of coil-end and pole-face effects, the
tostrictive. This is an additional potential source of error yokes should be thicker than the recommended minimum. For
FIG. 1 Basic Block Circuit Diagram of the Wattmeter Method
A 932/A932M
and number of significant digits shall be consistent with the
accuracy specified above. Care shall be taken to avoid errors
due to temperature and frequency effects in the instrument.
NOTE 3—Inaccuracies in setting the test voltage produce errors ap-
proximately two times as large in the specific core loss.
7.5 RMS Voltmeter, V — A true rms-indicating voltmeter
rms
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
voltmeter shall be the same as specified for the flux voltmeter.
FIG. 2 Single Yoke Fixture (Exploded View) Either digital or analog rms voltmeters are permitted. The
normally high input impedance of digital rms voltmeters is
calibration purposes, it is suggested that the width of the fixture
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 4 Epstein-type specimens.
of an analog rms voltmeter shall not be less than 10 000 V/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)
7.6 Wattmeter, W—The full-scale accuracy of the wattmeter
winding, shall be uniformly and closely wound on a non-
shall not be lower than 0.25 % at the test frequency and unity
magnetic, non-conducting coil form and each shall span the
power factor. The power factor encountered by a wattmeter
greatest possible distance between the pole faces of the yoke
during a core loss test on a specimen is always less than unity
fixture. It is recommended that the number of turns in the
and, at flux densities far above the knee of the magnetization
primary and secondary windings be equal. The number of turns
curve, approaches zero. The wattmeter must maintain 1.0 %
may be chosen to suit the instrumentation, mass of specimen
accuracy at the lowest power factor which is presented to it.
and test frequency. The secondary winding shall be the
Variable scaling devices may be employed to cause the
innermost winding. The primary and secondary turns shall be
wattmeter to indicate directly in units of specific core loss if the
wound in the same direction from a common starting point at
combination of basic instruments and scaling devices conforms
one end of the coil form. Also, to minimize self-impedances of
to the specifications stated here.
the windings, the opening in the coil form should be no greater
7.6.1 Electronic Digital Wattmeter—An electronic digital
than that required to allow easy insertion of the test specimen.
wattmeter is preferred in this test method because of its digital
Construction and mounting of the test coil assembly must be
read-out and its capability for direct interfacing with electronic
such that the test specimen will be maintained without me-
data acquisition systems. A combination True RMS Voltmeter-
chanical distortion in the plane established by the pole faces of
Wattmeter-RMS Ammeter is acceptable to reduce the number
the yoke(s) of the test fixture.
of instruments connected in the test circuit.
7.3 Air Flux Compensator—To provide a means of deter-
7.6.1.1 The voltage input circuitry of the electronic digital
mining intrinsic flux density in the test specimen, an air-core
wattmeter must have an input impedance sufficiently high so
mutual inductor shall constitute part of the test-coil system.
that connection to the secondary winding of the test fixture
The respective primary and secondary windings of the air-core
during testing does not change the terminal voltage of the
inductor and the test-specimen coil shall be connected in series
secondary by more than 0.05 %. Also, the voltage input
and the voltage polarities of the secondary windings shall be in
circuitry must be capable of accepting the maximum peak
opposition. By proper adjustment of the mutual inductance of
voltage which is induced in the secondary winding during
the air-core inductor, the average voltage developed across the
testing.
combined secondary windings is proportional to the intrinsic
7.6.1.2 The current input circuitry of the electronic digital
flux density in the test specimen. Directions for construction
wattmeter should have as low an input impedance as possible,
and adjustment of the air-core mutual inductor for air-flux are
preferably no more than 0.1V, otherwise the flux waveform
found in Annex A3.
distortion tends to be excessive. The effect of moderate
7.4 Flux Voltmeter, V —A full-wave, true average respond-
f
waveform distortion is addressed in 10.3. The current input
ing voltmeter, with scale readings in average volts times p
circuitry must be capable of accepting the maximum rms
. =2 /4 so that its indications will be identical with those of
current and the maximum peak current drawn by the primary
a true rms voltmeter on a pure sinusoidal voltage, shall be
winding of the test transformer when core loss tests are being
provided for evaluating the peak value of the test flux density.
performed. In particular, since the primary current will be very
To produce the estimated precision of test under this test
nonsinusoidal (peaked) if core loss tests are performed on a
method, the full-scale meter errors shall not exceed 0.25 %
specimen at flux densities above the knee of the magnetization
(Note 3). Either digital or analog flux voltmeters are permitted.
curve, the crest factor capability of the current input circuitry
Use of a digital flux voltmeter with high input impedance
should be 5 or more.
(typically, 10 MV) is recommended to minimize loading
effects and to reduce instrument loss compensation. If an 7.6.2 Electrodynamometer Wattmeter—A reflecting type as-
analog flux voltmeter is used, its input resistance shall be tatic electrodynamometer wattmeter is permitted as an alterna-
greater then 10 000 V/V of full scale indication. Voltage ranges tive to an electronic wattmeter.
A 932/A932M
7.6.2.1 The sensitivity of the electrodynamometer wattme- If desired, the value of the resistor may be such that the
ter must be such that the connection of the potential circuit of peak-reading voltmeter indicates directly in terms of peak
the wattmeter, during testing, to the secondary winding of the magnetic field strength, provided that the resistor conforms to
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