ASTM A912/A912M-11(2019)
(Test Method)Standard Test Method for Alternating-Current Magnetic Properties of Amorphous Materials at Power Frequencies Using Wattmeter-Ammeter-Voltmeter Method with Toroidal Specimens
Standard Test Method for Alternating-Current Magnetic Properties of Amorphous Materials at Power Frequencies Using Wattmeter-Ammeter-Voltmeter Method with Toroidal Specimens
SIGNIFICANCE AND USE
3.1 This test method provides a satisfactory means of determining various ac magnetic properties of amorphous magnetic materials.
3.2 The procedures described herein are suitable for use by producers and users of magnetic materials for materials specification acceptance and manufacturing control.
3.3 The procedures described herein may be adapted for use with specimens of other alloys and other toroidal forms.
SCOPE
1.1 This test method covers tests for various magnetic properties of amorphous materials at power frequencies [25 to 400 Hz] using a toroidal test transformer. The term “toroidal test transformer” is used to describe the test device, reserving the term “specimen” to refer to the material used in the test. The test specimen consists of toroidally wound flat strip.
1.2 This test method covers the determination of core loss, exciting power, rms and peak exciting current, several types of ac permeability, and related properties under ac magnetization at moderate and high inductions at power frequencies [25 to 70 Hz].
1.3 With proper instrumentation and specimen preparation, this test method is acceptable for measurements at frequencies from 5 Hz to 100 kHz. Proper instrumentation implies that all test instruments have the required frequency bandwidth. Also see Annex A2.
1.4 This test method also provides procedures for calculating impedance permeability from measured values of rms exciting current and for calculating ac peak permeability from measured peak values of total exciting current at magnetic field strengths up to about 10 Oe [796 A/m].
1.5 Explanations of symbols and brief definitions appear in the text of this test method. The official symbols and definitions are listed in Terminology A340.
1.6 This test method shall be used in conjunction with Practice A34/A34M.
1.7 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. 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.
1.8 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, health, and environmental practices and determine the applicability of regulatory limitations prior to use.
1.9 This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.
General Information
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Standards Content (Sample)
This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the
Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.
Designation: A912/A912M − 11 (Reapproved 2019)
Standard Test Method for
Alternating-Current Magnetic Properties of Amorphous
Materials at Power Frequencies Using Wattmeter-Ammeter-
Voltmeter Method with Toroidal Specimens
This standard is issued under the fixed designationA912/A912M; 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 of the other. Combining values from the two systems may
result in nonconformance with this standard.
1.1 This test method covers tests for various magnetic
1.8 This standard does not purport to address all of the
properties of amorphous materials at power frequencies [25 to
safety concerns, if any, associated with its use. It is the
400 Hz] using a toroidal test transformer. The term “toroidal
responsibility of the user of this standard to establish appro-
test transformer” is used to describe the test device, reserving
priate safety, health, and environmental practices and deter-
the term “specimen” to refer to the material used in the test.
mine the applicability of regulatory limitations prior to use.
The test specimen consists of toroidally wound flat strip.
1.9 This international standard was developed in accor-
1.2 This test method covers the determination of core loss,
dance with internationally recognized principles on standard-
exciting power, rms and peak exciting current, several types of
ization established in the Decision on Principles for the
ac permeability, and related properties under ac magnetization
Development of International Standards, Guides and Recom-
atmoderateandhighinductionsatpowerfrequencies[25to70
mendations issued by the World Trade Organization Technical
Hz].
Barriers to Trade (TBT) Committee.
1.3 With proper instrumentation and specimen preparation,
this test method is acceptable for measurements at frequencies
2. Referenced Documents
from 5 Hz to 100 kHz. Proper instrumentation implies that all
2.1 ASTM Standards:
test instruments have the required frequency bandwidth. Also
A34/A34MPractice for Sampling and Procurement Testing
see Annex A2.
of Magnetic Materials
1.4 This test method also provides procedures for calculat-
A340Terminology of Symbols and Definitions Relating to
ing impedance permeability from measured values of rms
Magnetic Testing
exciting current and for calculating ac peak permeability from
A343/A343MTest Method for Alternating-Current Mag-
measuredpeakvaluesoftotalexcitingcurrentatmagneticfield
netic Properties of Materials at Power Frequencies Using
strengths up to about 10 Oe [796 A/m].
Wattmeter-Ammeter-Voltmeter Method and 25-cm Ep-
stein Test Frame
1.5 Explanations of symbols and brief definitions appear in
A901Specification for Amorphous Magnetic Core Alloys,
thetextofthistestmethod.Theofficialsymbolsanddefinitions
Semi-Processed Types
are listed in Terminology A340.
C693Test Method for Density of Glass by Buoyancy
1.6 This test method shall be used in conjunction with
Practice A34/A34M.
3. Significance and Use
1.7 The values and equations stated in customary (cgs-emu
3.1 This test method provides a satisfactory means of
and inch-pound) units or SI units are to be regarded separately
determining various ac magnetic properties of amorphous
as standard. Within this standard, SI units are shown in
magnetic materials.
brackets. The values stated in each system may not be exact
3.2 The procedures described herein are suitable for use by
equivalents;therefore,eachsystemshallbeusedindependently
producers and users of magnetic materials for materials speci-
fication acceptance and manufacturing control.
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
Current edition approved April 1, 2019. Published April 2019. Originally contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM
approved in 1992. Last previous edition approved in 2011 as A912/A912M–11. Standards volume information, refer to the standard’s Document Summary page on
DOI: 10.1520/A0912_A0912M-11R19. the ASTM website.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
A912/A912M − 11 (2019)
3.3 Theproceduresdescribedhereinmaybeadaptedforuse 5.3 Instruments:
with specimens of other alloys and other toroidal forms.
5.3.1 Electronic digital instruments are preferred for use in
this test method. The use of analog instruments is permitted
4. Interferences
provided the requirements given in 5.3.2 – 5.5.2 as well as the
4.1 Test methods using toroidal test transformers are espe- requirements given in Test Method A343/A343M are met.
cially useful for evaluating the magnetic properties of a
5.3.1.1 Theelectricalimpedanceandaccuracyrequirements
material. There are, however, several important requirements
are given in 5.3.2 – 5.5.2. The operating principles for the
to be met when determining the material characteristics.
various instruments are not specified.
4.1.1 Theratioofinsidetooutsidediametermustbe0.82or
5.3.1.2 Combination instruments (volt-watt-ammeters) may
greater, or the magnetic field strength will be excessively
beusedprovidedtherequirementsgivenin5.3.2–5.5.2forthe
nonuniform throughout the test specimen and the measured
individual instruments are met.
parameters will not represent the basic material properties.
5.3.1.3 Automatic or data logging equipment may be used.
4.1.2 To best represent the average material properties, the
Itispreferablefortheoperatortohavearecordavailableofthe
cross-sectional area of the toroid should be uniform and the
specimen identification and measured values of the tests being
winding should be designed to avoid nonuniform induction.
performed.
4.1.3 Preparation of test specimens, especially of stress
5.3.1.4 Although electronic digital equipment usually fails
sensitivealloys,iscritical.Stressesthatareintroducedintoflat
catastrophically and errors are easily detected, it is incumbent
strip material when it is wound into a toroid depend on the
upon the user of this test method to ensure that the instruments
diameteroftheresultingtoroid,thethicknessanduniformityof
continue to meet the performance requirements.
the material, and the winding tension. These stresses shall be
5.3.2 Flux Voltmeter—A full-wave, true-average voltmeter,
removed or reduced by annealing. The annealing conditions
=2π
(time, temperature, and atmosphere) are a function of the
with scale reading in average volts times so that its
material chosen. The details of sample preparation must be
indications will be identical with those of a true rms voltmeter
agreed upon between the producer and user. Suggested condi-
on a pure sinusoidal voltage, shall be provided for evaluating
tions for preparation of amorphous specimens are contained in
the peak value of the test induction. To produce the estimated
Annex A2, Annex A3, Annex A4, and Annex A5.
precision of test under this test method, the full-scale meter
errorsshallnotexceed 60.25%(Note1).Metersof 60.5%or
5. Apparatus
more error may be used at reduced accuracy.
5.1 Theapparatusshallconsistofasmanyofthecomponent
5.3.3 RMS Voltmeter—Atrue rms-indicating voltmeter shall
parts shown in the basic block circuit diagram (Fig. 1)asare
be provided for evaluating the form factor of the voltage
required to perform the desired measurement functions.
induced in the secondary winding of the test fixture and for
5.2 Toroidal Test Transformer—The test transformer shall
evaluating the instrument losses. The accuracy of the rms
consist of a toroidal specimen, prepared as directed in Annex
voltmeter shall be the same as specified for the flux voltmeter.
A2, enclosed by primary and secondary windings. When the
5.3.3.1 The normally high input impedance of digital flux
test specimen is small or especially stressed, the use of a
and rms voltmeters will minimize loading effects and reduce
protective case, bobbin, spool, or core form is necessary, see
the magnitude of instrument losses to an insignificant value.
Annex A3.
5.3.3.2 Anelectronicscalingamplifiermaybeusedtocause
5.2.1 The primary and secondary windings may be any
the flux voltmeter and the rms voltmeter to indicate directly in
number of turns suited to the instrumentation, mass of
units of induction. The input impedance of the scaling ampli-
specimen, and test frequency. A 1:1 turns ratio is recom-
fier must be high enough to minimize loading effects and
mended.Anair-fluxcompensatoristobeusedwhenevertheair
instrumentlosses.Thecombinationofabasicinstrumentanda
flux is a measurable fraction of the total flux.
scalingdevicemustconformtothespecificationsstatedabove.
NOTE 1—Inaccuracies in setting the flux voltage produce errors
approximately two times as large in the specific core loss.
5.4 Wattmeter—The full-scale accuracy of the wattmeter
must not be poorer than 0.25% at the frequency of test and at
unity power factor. The power factor encountered by a watt-
meter during a core-loss test on a specimen is always less than
unityand,atinductionsfarabovethekneeofthemagnetization
curve,approacheszero.Thewattmetermustmaintainadequate
accuracy (1% of reading) even at the most severe (lowest)
power factor that is presented to it. Variable scaling devices
maybeusedtocausethewattmetertoindicatedirectlyinunits
ofspecificcorelossifthecombinationofbasicinstrumentand
scaling devices conforms to the specifications stated here.
5.4.1 Electronic Digital Wattmeter—An electronic digital
FIG. 1 Basic Circuit Diagram for Wattmeter Method wattmeter is preferred in this test method because of its high
A912/A912M − 11 (2019)
sensitivity, digital readout, and its capability for direct inter- a nominal full-scale accuracy of at least 3% at the test
facing with electronic data acquisition systems. frequency and be able to accommodate a voltage with a crest
factor of 5 or more.
5.4.1.1 The voltage input circuitry of the electronic digital
wattmeter must have an input impedance high enough that
5.6 Series Resistor—The standard series resistor (usually in
connection of the circuitry, during testing, to the secondary
the range 0.1 to 1.0 Ω) that carries the exciting current must
windingofthetestfixturedoesnotchangetheterminalvoltage
have adequate current-carrying capacity and be accurate to at
of the secondary by more than 0.05%.Also, the voltage input least 60.1%. It must have negligible temperature and fre-
circuitry must be capable of accepting the maximum peak quency variation with the conditions applicable to this test
voltage, which is induced in the secondary winding during method. If desired, the value of the resistor may be such that
testing. the peak-reading voltmeter indicates directly in terms of peak
magnetic field strength provided that the resistor conforms to
5.4.1.2 The current input circuitry of the electronic digital
the limitations stated herein.
wattmeter should have as low an input impedance as possible,
preferably no more than 0.1 Ω, otherwise the flux waveform 5.7 Power Supply—Asourceofsinusoidaltestpoweroflow
distortion can be corrected for as described in 9.3. The current internal impedance and excellent voltage and frequency stabil-
input circuitry must be capable of accepting the maximum rms ity is required for this test. The voltage for the test circuit may
be adjustable by use of a tapped transformer between the
current and the maximum peak current drawn by the primary
source and the test circuit or by generator field control. The
winding of the test transformer when core-loss tests are being
harmonic content of the voltage output from the source under
performed. In particular, since the primary current will be very
the heaviest test load should not exceed 1%. For testing at
nonsinusoidal (peaked) if core-loss tests are performed on a
commercial power frequencies, the volt-ampere rating of the
specimen at inductions above the knee of the magnetizing
source and its associated voltage control equipment should be
curve, the crest factor capability of the current input circuitry
adequate to supply the requirements of the test specimen
should be 4 or more.
without an excessive increase in the distortion of the voltage
5.4.2 Waveform Calculator—A waveform calculator, in
waveform. Voltage stability within 60.1% is necessary for
combination with a digitizing oscilloscope, may be used in
precise work. For testing at commercial frequencies, low-
place of the wattmeter for core-loss measurements, provided
distortion line voltage regulating equipment is available. The
that it meets the accuracy requirements given in 5.4. This
frequency of the source should be accurately controlled within
equipment is able to measure, compute, and display the rms,
60.1% of the nominal value.
average, and peak values for current and flux voltage, as well
5.7.1 An electronic power source consisting of a low-
as measure the core loss and excitation power demand. It is
distortion oscillator (Note 2) and a linear amplifier makes an
convenient for making a large number of repetitive measure-
acceptable source of test power. The form factor of the test
ments. See Appendix X2 for details regarding these instru-
=
2π
ments.
voltage should be as close to as practicable and must be
5.4.2.1 The current and flux sensing leads must be con-
within 61% of this value. The line power for the electronic
nected in the proper phase relationship.
oscillator and amplifier should come from a voltage-regulated
5.4.2.2 The normally high input impedance of these instru-
source to ensure voltage stability within 0.1%, and the output
ments(approximately1MΩ)reducespossibleerrorsasaresult ofthesystemshouldbemonitoredwithanaccuratefrequency-
of instrument loading to negligible levels.
indicating device to see that control of the frequency is
maintained to within 60.1% or better. It is permissible to use
5.5 Ammeters—Two types of current measurements are
an amplifier with negative feedback to reduce the waveform
used in conjunction with this test method: rms current values
distortion.
are used for calculating exciting power and impedance perme-
NOTE 2—It is advisable when testing at power line frequency to have
ability while peak current values are used for calculating peak
the oscillator synchronized with the power line.
permeability. The prefe
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