ASTM A804/A804M-04(2015)

Standard Test Methods for Alternating-Current Magnetic Properties of Materials at Power Frequencies Using Sheet-Type Test Specimens

SIGNIFICANCE AND USE
4.1 Materials Evaluation—These test methods were developed to supplement the testing of Epstein specimens for applications involving the use of flat, sheared laminations where the testing of Epstein specimens in either the as-sheared or stress-relief-annealed condition fails to provide the most satisfactory method of predicting magnetic performance in the application. As a principal example, the test methods have been found particularly applicable to the control and evaluation of the magnetic properties of thermally flattened, grain-oriented electrical steel (Condition F5, Specification A876) used as lamination stock for cores of power transformers. Inasmuch as the test methods can only be reliably used to determine unidirectional magnetic properties, the test methods have limited applicability to the testing of fully processed nonoriented electrical steels as normally practiced (Specification A677).  
4.2 Specification Acceptance—The reproducibility of test results and the accuracy relative to the 25-cm [250-mm] Epstein method of test are considered such as to render the test methods suitable for materials specification testing.  
4.3 Interpretation of Test Results—Because of specimen size, considerable variation in magnetic properties may be present within a single specimen or between specimens that may be combined for testing purposes. Also, variations may exist in test values that are combined to represent a test lot of material. Test results reported will therefore, in general, represent averages of magnetic quality and in certain applications, particularly those involving narrow widths of laminations, deviations in magnetic performance from those expected from reported data may occur at times. Additionally, application of test data to the design or evaluation of a particular magnetic device must recognize the influence of magnetic circuitry upon performance and the possible deterioration in magnetic properties arising from construction of the device.  
4.4 ...
SCOPE
1.1 These test methods cover the determination of specific core loss and peak permeability of single layers of sheet-type specimens tested with normal excitation at a frequency of 50 or 60 Hz.  
Note 1: These test methods have been applied only at the commercial power frequencies, 50 and 60 Hz, but with proper instrumentation and application of the principles of testing and calibration embodied in the test methods, they are believed to be adaptable to testing at frequencies ranging from 25 to 400 Hz.  
1.2 These test methods use calibration procedures that provide correlation with the 25-cm [250-mm] Epstein test.  
1.3 The range of test magnetic flux densities is governed by the properties of the test specimen and by the available instruments and other equipment components. Normally, nonoriented electrical steels can be tested over a range from 8 to 16 kG [0.8 to 1.6 T] for core loss. For oriented electrical steels, the normal range extends to 18 kG [1.8 T]. Maximum magnetic flux densities in peak permeability testing are limited principally by heating of the magnetizing winding and tests are limited normally to a maximum ac magnetic field strength of about 150 Oe [12 000 A/m].  
1.4 These test methods cover two alternative procedures as follows:
Test Method 1—Sections 6 – 12
Test Method 2—Sections 13 – 19  
1.4.1 Test Method 1 uses a test fixture having (1) two windings that encircle the test specimen, and (2) a ferromagnetic yoke structure that serves as the flux return path and has low core loss and low magnetic reluctance.  
1.4.2 Test Method 2 uses a test fixture having (1) two windings that encircle the test specimen, (2) a third winding located inside the other two windings and immediately adjacent to one surface of the test specimen, and (3) a ferromagnetic yoke structure which serves as the flux-return path and has low magnetic reluctance.  
1.5 The values and equations stated in customary (cgs-emu a...

General Information

• Status: Historical
• Publication Date: 30-Sep-2015
• ICS: 77.140.40 - Steels with special magnetic properties
• Technical Committee: A06 - Magnetic Properties
• Drafting Committee: A06.01 - Test Methods

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: A804/A804M − 04 (Reapproved 2015)
Standard Test Methods for
Alternating-Current Magnetic Properties of Materials at
Power Frequencies Using Sheet-Type Test Specimens
This standard is issued under the fixed designationA804/A804M; 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 netic yoke structure which serves as the flux-return path and
has low magnetic reluctance.
1.1 These test methods cover the determination of specific
1.5 The values and equations stated in customary (cgs-emu
core loss and peak permeability of single layers of sheet-type
and inch-pound) units or SI units are to be regarded separately
specimenstestedwithnormalexcitationatafrequencyof50or
as standard. Within this standard, SI units are shown in
60 Hz.
brackets except for the sections concerning calculations where
NOTE 1—These test methods have been applied only at the commercial
there are separate sections for the respective unit systems. The
power frequencies, 50 and 60 Hz, but with proper instrumentation and
values stated in each system may not be exact equivalents;
applicationoftheprinciplesoftestingandcalibrationembodiedinthetest
therefore,eachsystemshallbeusedindependentlyoftheother.
methods, they are believed to be adaptable to testing at frequencies
ranging from 25 to 400 Hz.
Combiningvaluesfromthetwosystemsmayresultinnoncon-
formance with this standard.
1.2 These test methods use calibration procedures that
provide correlation with the 25-cm [250-mm] Epstein test. 1.6 This standard does not purport to address all of the
safety concerns, if any, associated with its use. It is the
1.3 The range of test magnetic flux densities is governed by
responsibility of the user of this standard to establish appro-
the properties of the test specimen and by the available
priate safety and health practices and determine the applica-
instruments and other equipment components. Normally, non-
bility of regulatory limitations prior to use.
orientedelectricalsteelscanbetestedoverarangefrom8to16
kG[0.8to1.6T]forcoreloss.Fororientedelectricalsteels,the
2. Referenced Documents
normal range extends to 18 kG [1.8 T]. Maximum magnetic
flux densities in peak permeability testing are limited princi- 2.1 ASTM Standards:
A34/A34MPractice for Sampling and Procurement Testing
pally by heating of the magnetizing winding and tests are
of Magnetic Materials
limited normally to a maximum ac magnetic field strength of
A340Terminology of Symbols and Definitions Relating to
about 150 Oe [12000 A/m].
Magnetic Testing
1.4 These test methods cover two alternative procedures as
A343/A343MTest Method for Alternating-Current Mag-
follows:
netic Properties of Materials at Power Frequencies Using
Test Method 1—Sections6–12
Wattmeter-Ammeter-Voltmeter Method and 25-cm Ep-
Test Method 2—Sections13–19
stein Test Frame
1.4.1 Test Method 1 uses a test fixture having (1) two
A677Specification for Nonoriented Electrical Steel Fully
windings that encircle the test specimen, and (2) a ferromag-
Processed Types
netic yoke structure that serves as the flux return path and has
A683Specification for Nonoriented Electrical Steel, Semi-
low core loss and low magnetic reluctance.
processed Types
1.4.2 Test Method 2 uses a test fixture having (1) two
A876Specification for Flat-Rolled, Grain-Oriented, Silicon-
windings that encircle the test specimen, (2) a third winding
Iron, Electrical Steel, Fully Processed Types
located inside the other two windings and immediately adja-
cent to one surface of the test specimen, and (3) a ferromag-
3. Terminology
3.1 Definitions:
These test methods are under the jurisdiction of ASTM Committee A06 on
Magnetic Properties and are the direct responsibility of Subcommittee A06.01 on
Test Methods. For referenced ASTM standards, visit the ASTM website, www.astm.org, or
Current edition approved Oct. 1, 2015. Published October 2015. Originally contact ASTM Customer Service at [e-mail]. For Annual Book of ASTM
approved in 1982. Last previous edition approved in 2009 as A804/A804M–04 Standards volume information, refer to the standard’s Document Summary page on
ɛ1
(2009) . DOI: 10.1520/A0804_A0804M-04R15. the ASTM website.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
A804/A804M − 04 (2015)
3.1.1 General—The definitions of terms, symbols, and con- test data to the design or evaluation of a particular magnetic
version factors relating to magnetic testing found in Terminol- devicemustrecognizetheinfluenceofmagneticcircuitryupon
ogy A340 are used in these test methods. performance and the possible deterioration in magnetic prop-
erties arising from construction of the device.
3.2 Definitions of Terms Specific to This Standard:
3.2.1 sheet specimen—a rectangular specimen comprised of 4.4 Recommended Standard Tests—Thesetestmethodshave
a single piece of material or paralleled multiple strips of been principally applied to the magnetic testing of thermally
material arranged in a single layer. flattened, grain-oriented electrical steels at 50 and 60 Hz.
Specific core loss at 15 or 17 kG [1.5 or 1.7 T] and peak
4. Significance and Use
permeability (if required) at 10 Oe [796 A/m] are the recom-
4.1 Materials Evaluation—These test methods were devel- mended parameters for evaluating this class of material.
oped to supplement the testing of Epstein specimens for
5. Sampling
applications involving the use of flat, sheared laminations
5.1 LotSizeandSampling—Unlessotherwiseestablishedby
where the testing of Epstein specimens in either the as-sheared
mutualagreementbetweenthemanufacturerandthepurchaser,
or stress-relief-annealed condition fails to provide the most
determination of a lot size and the sampling of a lot to obtain
satisfactory method of predicting magnetic performance in the
sheets for specimen preparation shall follow the recommenda-
application.Asaprincipalexample,thetestmethodshavebeen
tions of Practice A34/A34M, Sections 5 and 6.
found particularly applicable to the control and evaluation of
the magnetic properties of thermally flattened, grain-oriented
METHOD 1 TWO-WINDING YOKE-FIXTURE TEST
electrical steel (Condition F5, Specification A876) used as
METHOD
lamination stock for cores of power transformers. Inasmuch as
the test methods can only be reliably used to determine
6. Basic Test Circuit
unidirectional magnetic properties, the test methods have
6.1 Fig. 1 provides a schematic circuit diagram for the test
limited applicability to the testing of fully processed nonori-
method.Apowersourceofpreciselycontrollableacsinusoidal
ented electrical steels as normally practiced (Specification
voltage is used to energize the primary circuit. To minimize
A677).
flux-waveform distortion, current ratings of the power source
4.2 Specification Acceptance—The reproducibility of test
and of the wiring and switches in the primary circuit shall be
results and the accuracy relative to the 25-cm [250-mm]
such as to provide very low impedance relative to the imped-
Epsteinmethodoftestareconsideredsuchastorenderthetest
ance arising from the test fixture and test specimen. Ratings of
methods suitable for materials specification testing.
switches and wiring in the secondary circuit also shall be such
astocausenegligiblevoltagedropbetweentheterminalsofthe
4.3 Interpretation of Test Results—Because of specimen
secondary test winding and the terminals of the measuring
size, considerable variation in magnetic properties may be
instruments.
present within a single specimen or between specimens that
may be combined for testing purposes. Also, variations may
7. Apparatus
exist in test values that are combined to represent a test lot of
7.1 The test circuit shall incorporate as many of the follow-
material. Test results reported will therefore, in general, repre-
ing components as are required to perform the desired mea-
sent averages of magnetic quality and in certain applications,
surements.
particularly those involving narrow widths of laminations,
deviations in magnetic performance from those expected from 7.2 Yoke Test Fixture—Fig. 2 and Fig. 3 show line drawings
reported data may occur at times. Additionally, application of ofasingle-yokefixtureandadouble-yokefixture,respectively.
FIG. 1 Basic Circuit Diagram for Method 1
A804/A804M − 04 (2015)
may be chosen to suit the instrumentation, mass of specimen
and test frequency. The secondary winding shall be the
innermost winding and, with instrumentation of suitably high
input resistance, normally may consist of a single layer. To
reduce self-impedance and thereby minimize flux-waveform
distortion, it is recommended that the primary winding consist
of multiple layers of equal turns connected in parallel. The
number of such layers should be optimized based on consid-
eration of a reduction in winding resistance versus an increase
ininductivereactanceatthethirdharmonicoftheprincipaltest
frequency used. The primary and secondary turns shall be
wound in the same direction from a common starting point at
FIG. 2 Single-Yoke Fixture (Exploded View)
one end of the coil form.Also, to minimize self-impedances of
thewindings,theopeninginthecoilformshouldbenogreater
than required to allow easy insertion of the test specimen.
Construction and mounting of the test coil assembly must be
such that the test specimen will be maintained without me-
chanical distortion in the plane established by the pole faces of
the yoke(s) of the test fixture.
7.3 Air-Flux Compensator—To provide a means of deter-
mining intrinsic induction in the test specimen, an air-core
mutual inductor shall constitute part of the test-coil system.
The respective primary and secondary windings of the air-core
inductorandthetest-specimencoilshallbeconnectedinseries
andthevoltagepolaritiesofthesecondarywindingsshallbein
opposition. By proper adjustment of the mutual inductance of
the air-core inductor, the average of the voltage developed
across the combined secondary windings is proportional to the
FIG. 3 Double-Yoke Fixture (Exploded View) intrinsic induction in the test specimen. Directions for con-
struction and adjustment of the air-core mutual inductor for
air-flux compensation are found in Annex A3.
A double-yoke fixture is preferred in this method but a
7.4 Flux Voltmeter, V—Afull-wave,true-averagevoltmeter,
single-yoke fixture is permitted. Directions concerning the f
with scale reading in average voltage times 1.111 so that its
design, construction, and calibration of the fixture are given in
indications will be identical with those of a true rms voltmeter
7.2.1, 7.2.2, Annex A1, and Annex A2.
on a pure sinusoidal voltage, shall be provided for evaluating
7.2.1 Yoke Structure—Various dimensions and fabrication
thepeakvalueofthetestmagneticfluxdensity.Toproducethe
procedures in construction are permissible. Since the recom-
estimated precision of test under this method, the full-scale
mended calibration procedure provides correlation with the
metererrorsshallnotexceed0.25%(Note2).Metersof0.5%
25-cm [250-mm] Epstein test, the minimum inside dimension
or more error may be used at reduced accuracy. Either digital
between pole faces must be at least 22 cm [220 mm]. The
or analog flux voltmeters are permitted. The normally high
thickness of the pole faces should be not less than 2.5 cm [25
input impedance of digital voltmeters is desirable to minimize
mm]. It is recognized that pole faces as narrow as 1.9 cm [19
loading effects and to reduce the magnitude of instrument loss
mm] are being used with nickel-iron yoke systems with good
compensations. The input resistance of an analog flux voltme-
results. To minimize the influences of coil-end and pole-face
ter shall not be less than 1000 Ω/V of full-scale indication. A
effects, the yokes should be longer than the recommended
resistive voltage divider, a standard-ratio transformer, or other
minimum. For calibration purposes, it is suggested that the
variablescalingdevicemaybeusedtocausethefluxvoltmeter
width of the fixture be such as to accommodate a specimen of
to indicate directly in units of magnetic flux density if the
at least 36-cm [360-mm] width which corresponds to the
combination of basic instrument and scaling device conforms
combined width of twelve Epstein-type specimens. Should the
to the specifications stated above.
fixturewidthbelessthan36cm[360mm],itwillbenecessary
to test each calibration specimen in two parts and average the
NOTE 2—Inaccuracies in setting the test voltage produce percentage
results.
errors approximately two times as large in the specific core loss. Care
should also be taken to avoid errors caused by temperature and frequency
7.2.2 Test Windings—The test windings, which shall consist
effects in the instrument.
of a primary (exciting) winding and a secondary (potential)
winding, shall be uniformly and closely wound on a 7.4.1 If used with a mutual inductor as a peak ammeter at
nonmagnetic, nonconducting coil form and each shall span the magnetic flux densities well above the knee of the magnetiza-
greatestpracticabledistancebetweenthepolefacesoftheyoke tion curve, the flux voltmeter must be capable of accurately
fixture. It is recommended that the number of turns in the measuringtheextremelynonsinusoidal(peaked)voltagethatis
primaryandsecondarywindingsbeequal.Thenumberofturns induced in the secondary winding of the mutual inductor.
A804/A804M − 04 (2015)
Additionally, if so used, an analog flux voltmeter should have suitable electronic digital wattmeter is permitted as an alterna-
an input resistance of 5000 to 10000 Ω/V of full-scale tive to an electrodynamometer wattmeter in this test method.
indication.
An electronic digital wattmeter oftentimes is preferred in this
test method because of its digital readout and its capability for
7.5 RMS Voltmeter, V —A true rms-indicating voltmeter
rms
direct interfacing with electronic data acquisition systems.
shall be provided for evaluating the form factor of the voltage
7.6.2.1 The voltage input circuitry of the electronic digital
induced in the secondary winding of the test fixture and for
wattmeter must have an input impedance sufficiently high that
evaluating the instrument losses. The accuracy of the rms
connection of the circuitry, during testing, to the secondary
voltmeter shall be the same as that specified for the flux
voltmeter. Either digital or analog rms voltmeters are permit- windingofthetestfixturedoesnotchangetheterm
...

This document is not an ASTM standard and is intended only to provide the user of an ASTM standard an indication of what changes have been made to the previous version. Because
it may not be technically possible to adequately depict all changes accurately, ASTM recommends that users consult prior editions as appropriate. In all cases only the current version
of the standard as published by ASTM is to be considered the official document.
´1
Designation: A804/A804M − 04 (Reapproved 2009) A804/A804M − 04 (Reapproved 2015)
Standard Test Methods for
Alternating-Current Magnetic Properties of Materials at
Power Frequencies Using Sheet-Type Test Specimens
This standard is issued under the fixed designation A804/A804M; 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.
ε NOTE—Editorial changes were made throughout in May 2009.
1. Scope
1.1 These test methods cover the determination of specific core loss and peak permeability of single layers of sheet-type
specimens tested with normal excitation at a frequency of 50 or 60 Hz.
NOTE 1—These test methods have been applied only at the commercial power frequencies, 50 and 60 Hz, but with proper instrumentation and
application of the principles of testing and calibration embodied in the test methods, they are believed to be adaptable to testing at frequencies ranging
from 25 to 400 Hz.
1.2 These test methods use calibration procedures that provide correlation with the 25-cm [250-mm] Epstein test.
1.3 The range of test magnetic flux densities is governed by the properties of the test specimen and by the available instruments
and other equipment components. Normally, nonoriented electrical steels can be tested over a range from 8 to 16 kG [0.8 to 1.6
T] for core loss. For oriented electrical steels, the normal range extends to 18 kG [1.8 T]. Maximum magnetic flux densities in peak
permeability testing are limited principally by heating of the magnetizing winding and tests are limited normally to a maximum
ac magnetic field strength of about 150 Oe [12 000 A/m].
1.4 These test methods cover two alternative procedures as follows:
Test Method 1—Sections 6 – 12
Test Method 2—Sections 13 – 19
1.4.1 Test Method 1 uses a test fixture having (1) two windings that encircle the test specimen, and (2) a ferromagnetic yoke
structure that serves as the flux return path and has low core loss and low magnetic reluctance.
1.4.2 Test Method 2 uses a test fixture having (1) two windings that encircle the test specimen, (2) a third winding located inside
the other two windings and immediately adjacent to one surface of the test specimen, and (3) a ferromagnetic yoke structure which
serves as the flux-return path and has low magnetic reluctance.
1.5 The values and equations stated in customary (cgs-emu and inch-pound) units 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.
1.6 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.
2. Referenced Documents
2.1 ASTM Standards:
A34/A34M Practice for Sampling and Procurement Testing of Magnetic Materials
A340 Terminology of Symbols and Definitions Relating to Magnetic Testing
These test methods are under the jurisdiction of ASTM Committee A06 on Magnetic Properties and are the direct responsibility of Subcommittee A06.01 on Test
Methods.
Current edition approved May 1, 2009Oct. 1, 2015. Published January 2010October 2015. Originally approved in 1982. Last previous edition approved in 20042009 as
ɛ1
A804/A804M–04. –04 (2009) . DOI: 10.1520/A0804_A0804M-04R09E01.10.1520/A0804_A0804M-04R15.
For referenced ASTM standards, visit the ASTM website, www.astm.org, or contact ASTM Customer Service at [e-mail]. For Annual Book of ASTM Standards
volume information, refer to the standard’s Document Summary page on the ASTM website.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
A804/A804M − 04 (2015)
A343/A343M Test Method for Alternating-Current Magnetic Properties of Materials at Power Frequencies Using Wattmeter-
Ammeter-Voltmeter Method and 25-cm Epstein Test Frame
A677 Specification for Nonoriented Electrical Steel Fully Processed Types
A683 Specification for Nonoriented Electrical Steel, Semiprocessed Types
A876 Specification for Flat-Rolled, Grain-Oriented, Silicon-Iron, Electrical Steel, Fully Processed Types
3. Terminology
3.1 Definitions:
3.1.1 General—The definitions of terms, symbols, and conversion factors relating to magnetic testing found in Terminology
A340 are used in these test methods.
3.2 Definitions of Terms Specific to This Standard:
3.2.1 sheet specimen—a rectangular specimen comprised of a single piece of material or paralleled multiple strips of material
arranged in a single layer.
4. Significance and Use
4.1 Materials Evaluation—These test methods were developed to supplement the testing of Epstein specimens for applications
involving the use of flat, sheared laminations where the testing of Epstein specimens in either the as-sheared or stress-relief-
annealed condition fails to provide the most satisfactory method of predicting magnetic performance in the application. As a
principal example, the test methods have been found particularly applicable to the control and evaluation of the magnetic properties
of thermally flattened, grain-oriented electrical steel (Condition F5, Specification A876) used as lamination stock for cores of
power transformers. Inasmuch as the test methods can only be reliably used to determine unidirectional magnetic properties, the
test methods have limited applicability to the testing of fully processed nonoriented electrical steels as normally practiced
(Specification A677).
4.2 Specification Acceptance—The reproducibility of test results and the accuracy relative to the 25-cm [250-mm] Epstein
method of test are considered such as to render the test methods suitable for materials specification testing.
4.3 Interpretation of Test Results—Because of specimen size, considerable variation in magnetic properties may be present
within a single specimen or between specimens that may be combined for testing purposes. Also, variations may exist in test values
that are combined to represent a test lot of material. Test results reported will therefore, in general, represent averages of magnetic
quality and in certain applications, particularly those involving narrow widths of laminations, deviations in magnetic performance
from those expected from reported data may occur at times. Additionally, application of test data to the design or evaluation of
a particular magnetic device must recognize the influence of magnetic circuitry upon performance and the possible deterioration
in magnetic properties arising from construction of the device.
4.4 Recommended Standard Tests—These test methods have been principally applied to the magnetic testing of thermally
flattened, grain-oriented electrical steels at 50 and 60 Hz. Specific core loss at 15 or 17 kG [1.5 or 1.7 T] and peak permeability
(if required) at 10 Oe [796 A/m] are the recommended parameters for evaluating this class of material.
5. Sampling
5.1 Lot Size and Sampling—Unless otherwise established by mutual agreement between the manufacturer and the purchaser,
determination of a lot size and the sampling of a lot to obtain sheets for specimen preparation shall follow the recommendations
of Practice A34/A34M, Sections 5 and 6.
METHOD 1 TWO-WINDING YOKE-FIXTURE TEST METHOD
6. Basic Test Circuit
6.1 Fig. 1 provides a schematic circuit diagram for the test method. A power source of precisely controllable ac sinusoidal
voltage is used to energize the primary circuit. To minimize flux-waveform distortion, current ratings of the power source and of
the wiring and switches in the primary circuit shall be such as to provide very low impedance relative to the impedance arising
from the test fixture and test specimen. Ratings of switches and wiring in the secondary circuit also shall be such as to cause
negligible voltage drop between the terminals of the secondary test winding and the terminals of the measuring instruments.
7. Apparatus
7.1 The test circuit shall incorporate as many of the following components as are required to perform the desired measurements.
7.2 Yoke Test Fixture—Fig. 2 and Fig. 3 show line drawings of a single-yoke fixture and a double-yoke fixture, respectively. A
double-yoke fixture is preferred in this method but a single-yoke fixture is permitted. Directions concerning the design,
construction, and calibration of the fixture are given in 7.2.1, 7.2.2, Annex A1, and Annex A2.
7.2.1 Yoke Structure—Various dimensions and fabrication procedures in construction are permissible. Since the recommended
calibration procedure provides correlation with the 25-cm [250-mm] Epstein test, the minimum inside dimension between pole
A804/A804M − 04 (2015)
FIG. 1 Basic Circuit Diagram for Method 1
FIG. 2 Single-Yoke Fixture (Exploded View)
FIG. 3 Double-Yoke Fixture (Exploded View)
faces must be at least 22 cm [220 mm]. The thickness of the pole faces should be not less than 2.5 cm [25 mm]. It is recognized
that pole faces as narrow as 1.9 cm [19 mm] are being used with nickel-iron yoke systems with good results. To minimize the
influences of coil-end and pole-face effects, the yokes should be longer than the recommended minimum. For calibration purposes,
it is suggested that the width of the fixture be such as to accommodate a specimen of at least 36-cm [360-mm] width which
corresponds to the combined width of twelve Epstein-type specimens. Should the fixture width be less than 36 cm [360 mm], it
will be necessary to test each calibration specimen in two parts and average the results.
7.2.2 Test Windings—The test windings, which shall consist of a primary (exciting) winding and a secondary (potential)
winding, shall be uniformly and closely wound on a nonmagnetic, nonconducting coil form and each shall span the greatest
practicable distance between the pole faces of the yoke fixture. It is recommended that the number of turns in the primary and
A804/A804M − 04 (2015)
secondary windings be equal. The number of turns may be chosen to suit the instrumentation, mass of specimen and test frequency.
The secondary winding shall be the innermost winding and, with instrumentation of suitably high input resistance, normally may
consist of a single layer. To reduce self-impedance and thereby minimize flux-waveform distortion, it is recommended that the
primary winding consist of multiple layers of equal turns connected in parallel. The number of such layers should be optimized
based on consideration of a reduction in winding resistance versus an increase in inductive reactance at the third harmonic of the
principal test frequency used. The primary and secondary turns shall be wound in the same direction from a common starting point
at one end of the coil form. Also, to minimize self-impedances of the windings, the opening in the coil form should be no greater
than required to allow easy insertion of the test specimen. Construction and mounting of the test coil assembly must be such that
the test specimen will be maintained without mechanical distortion in the plane established by the pole faces of the yoke(s) of the
test fixture.
7.3 Air-Flux Compensator—To provide a means of determining intrinsic induction in the test specimen, an air-core mutual
inductor shall constitute part of the test-coil system. The respective primary and secondary windings of the air-core inductor and
the test-specimen coil shall be connected in series and the voltage polarities of the secondary windings shall be in opposition. By
proper adjustment of the mutual inductance of the air-core inductor, the average of the voltage developed across the combined
secondary windings is proportional to the intrinsic induction in the test specimen. Directions for construction and adjustment of
the air-core mutual inductor for air-flux compensation are found in Annex A3.
7.4 Flux Voltmeter, V —A full-wave, true-average voltmeter, with scale reading in average voltage times 1.111 so that its
f
indications will be identical with those of a true rms voltmeter on a pure sinusoidal voltage, shall be provided for evaluating the
peak value of the test magnetic flux density. To produce the estimated precision of test under this method, the full-scale meter errors
shall not exceed 0.25 % (Note 2). Meters of 0.5 % or more error may be used at reduced accuracy. Either digital or analog flux
voltmeters are permitted. The normally high input impedance of digital voltmeters is desirable to minimize loading effects and to
reduce the magnitude of instrument loss compensations. The input resistance of an analog flux voltmeter shall not be less than 1000
Ω/V of full-scale indication. A resistive voltage divider, a standard-ratio transformer, or other variable scaling device may be used
to cause the flux voltmeter to indicate directly in units of magnetic flux density if the combination of basic instrument and scaling
device conforms to the specifications stated above.
NOTE 2—Inaccuracies in setting the test voltage produce percentage errors approximately two times as large in the specific core loss. Care should also
be taken to avoid errors caused by temperature and frequency effects in the instrument.
7.4.1 If used with a mutual inductor as a peak ammeter at magnetic flux densities well above the knee of the magnetization
curve, the flux voltmeter must be capable of accurately measuring the extremely nonsinusoidal (peaked) voltage that is induced
in the secondary winding of the mutual inductor. Additionally, if so used, an analog flux voltmeter should have an input resistance
of 5000 to 10 000 Ω/V of full-scale indication.
7.5 RMS Voltmeter, V —A true rms-indicating voltmeter shall be provided for evaluating the form factor of the voltage
rms
induced in the secondary winding of the test fixture and for evaluating the instrument losses. The accuracy of the rms voltmeter
shall be
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