ASTM A912/A912M-11(2019)

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 preferred method for measuring exciting
5.8 Test Fixture—Atest fixture (board, panel, or console) is
current is to measure the voltage drop across a low value,
recommended for convenience in testing. The test fixture shall
noninductive resistor in series with the primary windings.
consist of terminals for connecting a power source,
5.5.1 rms Ammeter—A true rms voltmeter in parallel with
instrumentation,thetesttransformer,andnecessaryswitches.It
the series resistor is required if measurements of rms exciting
may also contain the standard series current-sensing precision
current are to be made; rms exciting power, rms specific
resistor.
exciting power, and impedance permeability are calculated
from rms exciting current values. A nominal 1% accuracy is 6. Basic Circuit
required for this instrument.
6.1 Fig. 1 shows the essential apparatus and basic circuit
5.5.2 Peak Ammeter—The peak ammeter consists of a
connections for this test. Terminals 1 and 2 are connected to a
voltmeter whose indications are proportional to the peak-to-
source of adjustable ac voltage of sinusoidal waveform and
peak value of the voltage drop that results when the exciting
sufficient power rating to energize the primary circuit without
current flows through a low value of standard resistance appreciablevoltagedropinthesourceimpedance.Theprimary
connected in series with the primary winding of the test
circuitswitches,S andS ,aswellasallprimarycircuitwiring,
1 2
transformer. This peak-to-peak reading voltmeter should have should be capable of carrying much higher currents than
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normally are encountered to limit primary circuit resistance to 8.3 Setting Induction—With the required apparatus con-
values that will not cause appreciable distortion of the flux nectedasinFig.1,andwithTerminals1and2connectedtothe
waveform in the specimen when relatively high nonsinusoidal
powersource,thenwithswitchesS andS closedandS open,
1 3 2
currentsarebeingdrawn.Aprimarycircuitcurrentratingof10
adjust the voltage of the power supply to a point at which the
A is usually adequate for this purpose.
flux voltmeter indicates the value of voltage calculated to give
6.1.1 Although the current drain in the secondary circuit is
the desired test induction in accordance with Eq 1 or Eq 14.
quite small, the switches and wiring of these circuits should be
8.4 Core Loss—When the voltage indicated by the flux
rated for at least 1 A to ensure that the lead resistance is so
voltmeter has been adjusted to the desired value, read the
small that the voltage available at the terminals of all instru-
wattmeter.The combined resistance load of the flux voltmeter,
ments is imperceptibly lower than the voltage at the secondary
rms voltmeter, and potential circuit of the wattmeter will
terminals of the toroidal test transformer.
constitute the total instrument burden on the wattmeter. When
6.2 Fig. 2 shows an alternate set of instruments that may be
instruments other than high impedance electronic types are
used for this test.
used, exercise care so that the combined current drain of the
instrumentsdoesnotcauseanappreciablylargevoltagedropin
7. Sampling and Test Specimens
the secondary circuit resistance of the test frame. In such a
7.1 The test specimens for this test method shall be selected
case, the true induction in the specimens may be appreciably
and prepared for testing in accordance with provisions of
higher than is apparent from the voltage measured at the
Section 6 of Practice A34/A34M. Recommended practices are
secondary terminals of the test frame. In any event, power
given in Annex A2, Annex A3, Annex A4, and Annex A5 of
causedbyanycurrentdraininthesecondarycircuitatthetime
this test method.
ofreadingthewattmetermustbeknownsoitcanbesubtracted
from the wattmeter indications to obtain the net watts as a
8. Procedure
result of core loss.
8.1 Determine the mass, inner diameter, and outer diameter
of the toroidal test specimen with sufficient accuracy that the 8.5 Secondary (Induced) RMS Voltage—Measure the rms
inductionmaybecalculatedto 60.1%.Recordthesevaluesso
valueofthesecondaryvoltagebyhavingbothS andS closed
1 2
that the tests may be repeated or verified.
and the voltage adjusted to indicate the correct value of flux
voltage. On truly sinusoidal voltage, both voltmeters will
8.2 Demagnetization—The specimen should be demagne-
indicate the same value, showing that the form factor of the
tizedbeforemeasurementsofanymagneticpropertyaremade.
=
With the required apparatus connected as shown in Fig. 1, and 2π
induced voltage is . When the voltmeters give different
with switches S and S closed and S open, accomplish this 4
1 2 3
readings,theratioofthermsvaluetothatoftheformfactorof
demagnetizationbyinitiallyapplyingavoltagefromthepower
source to the primary circuit, which is sufficient to magnetize =2π
the induced voltage deviates from the desired value of .
the specimen to an induction above the knee of its magnetiza- 4
Determining the induction from the readings of a flux voltme-
tion curve, and then decrease the voltage slowly and smoothly
ter assures that the correct value of peak induction is achieved
(or in small steps) to a very low induction. (Induction may be
in the specimen, and hence, that the hysteresis component of
determined from the reading of the flux voltmeter by means of
the core loss is correct even if the waveform is not strictly
Eq 1 or Eq 14). After this demagnetization, test promptly for
the desired test points. When multiple test points are required, sinusoidal. But the eddy-current component of the core loss,
perform the tests in order of increasing induction values. being due to current resulting from a nonsinusoidal voltage
induced in the cross section of the strip, will be in error
depending on the deviation of the induced voltage from the
desired sinusoidal wave shape. This error in the eddy-current
component of loss can be corrected for some materials by
calculationsbasedontheobservedformfactorandtheapproxi-
mate percentage of eddy-current loss for the grade of material
being tested, if the correction is reasonably small. The equa-
tions involved in determining this correction are given in 9.3.
8.6 RMS Exciting Current—Measure the rms exciting
current, when required, with S closed and S and S open;
1 2 3
adjust the voltage from the power source to the desired test
induction and read the ammeter. If the current drain of the two
voltmeters in the secondary circuit is not negligible, they
should be disconnected when reading the ammeter; rms excit-
ing current may be used to calculate values of exciting power
or specific exciting power (see 9.4 or 10.4), rms exciting force
(see 9.5.1 or 10.5.1), ac magnetic field strength (see 9.5.2 or
FIG. 2 Basic Circuit Diagram for Waveform Calculator Method 10.5.2), or impedance permeability (see 9.7.2 or 10.7.2).
A912/A912M − 11 (2019)
8.7 Peak Current—When peak permeability at a given peak where:
magnetic field strength is required, open S and S for a
...