ASTM A912-93(1998)

NOTICE: This standard has either been superseded and replaced by a new version or withdrawn.
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Designation:A 912–93 (Reapproved 1998)
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 designation A 912; 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 (ε) 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 amorphous materials at power frequencies [25 to
400Hz]usingatoroidaltesttransformer.Thetermtoroidaltest
2. Referenced Documents
transformer is used to describe the test device reserving the
2.1 ASTM Standards:
term specimen to refer to the material used in the test.The test
A34/A34M Practice for Sampling and Procurement Test-
specimen consists of toroidally wound flat strip.
ing of Magnetic Materials
1.2 This test method covers the determination of core loss,
A340 Terminology of Symbols and Definitions Relating to
exciting power, rms and peak exciting current, several types of
Magnetic Testing
ac permeability, and related properties under ac magnetization
A343 Test Method forAlternating-Current Magnetic Prop-
atmoderateandhighinductionsatpowerfrequencies[25to70
ertiesofMaterialsatPowerFrequenciesUsingWattmeter-
Hz].
Ammeter-Voltmeter Method and 25-cm Epstein Test
1.3 With proper instrumentation and specimen preparation,
Frame
this test method is acceptable for measurements at frequencies
A901 Specification for Amorphous Magnetic Core Alloys,
from 5 Hz to 100 kHz. Proper instrumentation implies that all
Semi-Processed Types
test instruments have the required frequency bandwidth. Also
C693 Test Method for Density of Glass by Buoyancy
see Annex A2.
1.4 This test method also provides procedures for calculat- 3. Significance and Use
ing impedance permeability from measured values of rms
3.1 This test method provides a satisfactory means of
exciting current and for calculating ac peak permeability from
determining various ac magnetic properties of amorphous
measured peak values of total exciting current at magnetizing
magnetic materials.
forces up to about 10 Oe [796 A/m].
3.2 The procedures described herein are suitable for use by
1.5 Explanation of symbols and brief definitions appear in
manufacturers and users of magnetic materials for materials
thetextofthistestmethod.Theofficialsymbolsanddefinitions
specification acceptance and manufacturing control.
are listed in Terminology A340.
3.3 Theproceduresdescribedhereinmaybeadaptedforuse
1.6 This test method shall be used in conjunction with
with specimens of other alloys and other toroidal forms.
Practice A34/A34M.
4. Interferences
1.7 The values stated in either customary (cgs-emu and
inch-pound) units or SI units are to be regarded separately as
4.1 Test methods using toroidal test transformers are espe-
standard. Within the text, the SI units are shown in brackets.
cially useful for evaluating the magnetic properties of a
The values stated in each system are not exact equivalents;
material. There are, however, several important requirements
therefore,eachsystemshallbeusedindependentlyoftheother.
to be met when determining the material characteristics.
Combiningvaluesfromthetwosystemsmayresultinnoncon-
4.1.1 Theratioofthemeandiametertoradialbuild(annular
formance with this test method.
width)mustbeatleasttentoone,orthemagnetizingforcewill
1.8 This standard does not purport to address all of the
be excessively nonuniform throughout the test specimen and
safety concerns, if any, associated with its use. It is the
the measured parameters will not represent the basic material
properties.
This test method is under the jurisdiction of ASTM Committee A-6 on
MagneticPropertiesandisthedirectresponsibilityofSubcommitteeA06.01onTest
Methods.
Current edition approved Sept. 15, 1993. Published November 1993. Originally Annual Book of ASTM Standards, Vol 03.04.
published as A912–92. Last previous edition A912–92. Annual Book of ASTM Standards, Vol 15.02.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.
A 912
4.1.2 To best represent the average material properties, the 5.3.1.3 Automatic or data logging equipment may be used.
cross-sectional area of the toroid should be uniform and the Itispreferablefortheoperatortohavearecordavailableofthe
winding should be designed to avoid nonuniform induction. specimen identification and measured values of the tests being
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
with scale reading in average volts times 2p 4 so that its
=
(time, temperature, and atmosphere) are a function of the
/
indications will be identical with those of a true rms voltmeter
material chosen. The details of sample preparation must be
on a pure sinusoidal voltage, shall be provided for evaluating
agreed upon between the manufacturer and user. Suggested
the peak value of the test induction. To produce the estimated
conditions for preparation of amorphous specimens are con-
precision of test under this test method, the full-scale meter
tained in Annex A2, Annex A3, Annex A4, and Annex A5.
errorsshallnotexceed60.25%(Note1).Metersof 60.5%or
more error may be used at reduced accuracy.
5. Apparatus
5.3.3 RMSVoltmeter—Atruerms-indicatingvoltmetershall
5.1 Theapparatusshallconsistofasmanyofthecomponent
be provided for evaluating the form factor of the voltage
parts shown in the basic block circuit diagram (Fig. 1) as are
induced in the secondary winding of the test fixture and for
required to perform the desired measurement functions.
evaluating the instrument losses. The accuracy of the rms
5.2 Toroidal Test Transformer—The test transformer shall voltmeter shall be the same as specified for the flux voltmeter.
consist of a toroidal specimen, prepared as directed in Annex
5.3.3.1 The normally high-input impedance of digital flux
A2, enclosed by primary and secondary windings. When the and rms voltmeters will minimize loading effects and reduce
test specimen is small or especially stressed, the use of a the magnitude of instrument losses to an insignificant value.
protective case, bobbin, spool, or core form is necessary. 5.3.3.2 Anelectronicscalingamplifiermaybeusedtocause
the flux voltmeter and the rms voltmeter to indicate directly in
5.2.1 The primary and secondary windings may be any
units of induction. The input impedance of the scaling ampli-
number of turns suited to the instrumentation, mass of speci-
fier must be high enough to minimize loading effects and
men, and test frequency.A1:1 turns ratio is recommended.An
instrumentlosses.Thecombinationofabasicinstrumentanda
air-flux compensator is to be used whenever the air flux is a
scalingdevicemustconformtothespecificationsstatedabove.
measurable fraction of the total flux.
5.3 Instruments:
NOTE 1—Inaccuracies in setting the flux voltage produce errors ap-
proximately two times as large in the specific core loss.
5.3.1 Electronic digital instruments are preferred for use in
this test method. The use of analog instruments is permitted
5.4 Wattmeter—The full-scale accuracy of the wattmeter
provided the requirements given in 5.3.2-5.5.2 as well as the
must not be poorer than 0.25% at the frequency of test and at
requirements given in Test Method A343 are met.
unity power factor. The power factor encountered by a watt-
5.3.1.1 Theelectricalimpedanceandaccuracyrequirements
meter during a core-loss test on a specimen is always less than
are given in 5.3.2-5.5.2. The operating principles for the
unityand,atinductionsfarabovethekneeofthemagnetization
various instruments are not specified.
curve,approacheszero.Thewattmetermustmaintainadequate
accuracy (1% of reading) even at the most severe (lowest)
5.3.1.2 Combination instruments (volt-watt-ammeters) may
power factor that is presented to it. Variable scaling devices
be used provided the requirements given in 5.3.2-5.5.2 for the
maybeusedtocausethewattmetertoindicatedirectlyinunits
individual instruments are met.
of specific core loss if the combination of basic instrument and
scaling devices conforms to the specifications stated here.
5.4.1 Electronic Digital Wattmeter—An electronic digital
wattmeter is preferred in this test method because of its high
sensitivity, digital readout, and its capability for direct inter-
facing with electronic data acquisition systems.
5.4.1.1 The voltage input circuitry of the electronic digital
wattmeter must have an input impedance high enough that
connection of the circuitry, during testing, to the secondary
windingofthetestfixturedoesnotchangetheterminalvoltage
of the secondary by more than 0.05%.Also, the voltage input
circuitry must be capable of accepting the maximum peak
voltage, which is induced in the secondary winding during
testing.
5.4.1.2 The current input circuitry of the electronic digital
wattmeter should have as low an input impedance as possible,
FIG. 1 Basic Circuit Diagram for Wattmeter Method preferably no more than 0.1 Ω, otherwise the flux waveform
A 912
distortion can be corrected for as described in 9.3. The current be adjustable by use of a tapped transformer between the
input circuitry must be capable of accepting the maximum rms source and the test circuit or by generator field control. The
current and the maximum peak current drawn by the primary harmonic content of the voltage output from the source under
winding of the test transformer when core-loss tests are being the heaviest test load should not exceed 1%. For testing at
performed. In particular, since the primary current will be very commercial power frequencies, the volt-ampere rating of the
nonsinusoidal (peaked) if core-loss tests are performed on a source and its associated voltage control equipment should be
specimen at inductions above the knee of the magnetizing adequate to supply the requirements of the test specimen
curve, the crest factor capability of the current input circuitry without an excessive increase in the distortion of the voltage
should be 4 or more. waveform. Voltage stability within 60.1% is necessary for
precise work. For testing at commercial frequencies, low-
5.4.2 Waveform Calculator—A waveform calculator, in
distortion line voltage regulating equipment is available. The
combination with a digitizing oscilloscope, may be used in
frequency of the source should be accurately controlled within
place of the wattmeter for core-loss measurements, provided
60.1% of the nominal value.
that it meets the accuracy requirements given in 5.4. This
5.7.1 An electronic power source consisting of a low-
equipment is able to measure, compute, and display the rms,
distortion oscillator (Note 2) and a linear amplifier makes an
average, and peak values for current and flux voltage, as well
acceptable source of test power. The form factor of the test
as measure the core loss and excitation power demand. It is
voltageshouldbeascloseto 2p 4aspracticableandmust
convenient for making a large number of repetitive measure- =
/
bewithin 61%ofthisvalue.Thelinepowerfortheelectronic
ments. See Appendix X2 for details regarding these instru-
oscillator and amplifier should come from a voltage-regulated
ments.
source to ensure voltage stability within 0.1%, and the output
5.4.2.1 The current and flux sensing leads must be con-
ofthesystemshouldbemonitoredwithanaccuratefrequency-
nected in the proper phase relationship.
indicating device to see that control of the frequency is
5.4.2.2 The normal high input impedance of these instru-
maintained to within 60.1% or better. It is permissible to use
ments(approximately1MΩ)reducespossibleerrorsasaresult
an amplifier with negative feedback to reduce the waveform
of instrument loading to negligible levels.
distortion.
5.5 Ammeters—Two types of current measurements are
used in conjunction with this test method. Rms current values NOTE 2—It is advisable when testing at power line frequency to have
the oscillator synchronized with the power line.
are used for calculating exciting power and impedance perme-
ability while peak current values are used for calculating peak
5.8 Test Fixture—Atest fixture (board, panel, or console) is
permeability. The preferred method for measuring exciting
recommended for convenience in testing. The test fixture shall
current is to measure the voltage drop across a low value,
consist of terminals for connecting a power source, instrumen-
noninductive resistor in series with the primary windings.
tation,thetesttransformer,andnecessaryswitches.Itmayalso
5.5.1 RMS Ammeter—Atrue rms voltmeter in parallel with
contain the standard series current-sensing precision resistor.
the series resistor is required if measurements of rms exciting
6. Basic Circuit
current are to be made. Rms exciting power, rms specific
exciting power, and impedance permeability are calculated
6.1 Fig. 1 shows the essential apparatus and basic circuit
from rms exciting current values. A nominal 1% accuracy is
connections for this test. Terminals 1 and 2 are connected to a
required for this instrument.
source of adjustable ac voltage of sinusoidal waveform and
5.5.2 Peak Ammeter—The peak ammeter consists of a
sufficient power rating to energize the primary circuit without
voltmeter whose indications are proportional to the peak-to-
appreciablevoltagedropinthesourceimpedance.Theprimary
peak value of the voltage drop that results when the exciting
circuitswitches,S andS ,aswellasallprimarycircuitwiring,
1 2
current flows through a low value of standard resistance
should be capable of carrying much higher currents than
connected in series with the primary winding of the test
normally are encountered to limit primary circuit resistance to
transformer. This peak-to-peak reading voltmeter should have
val
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