ASTM A927/A927M-18(2022)

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: A927/A927M − 18 (Reapproved 2022)
Standard Test Method for
Alternating-Current Magnetic Properties of Toroidal Core
Specimens Using the Voltmeter-Ammeter-Wattmeter
Method
This standard is issued under the fixed designationA927/A927M; 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 2. Referenced Documents
1.1 This test method covers the determination of several ac 2.1 ASTM Standards:
magnetic properties of either laminated ring or toroidal tape A34/A34MPractice for Sampling and Procurement Testing
wound cores made from flat rolled product. of Magnetic Materials
A340Terminology of Symbols and Definitions Relating to
1.2 This test method covers test equipment and procedures
Magnetic Testing
fordeterminationofspecificcoreloss,specificexcitingpower,
A697/A697MTestMethodforAlternatingCurrentMagnetic
and peak permeability for power and audio frequencies (50Hz
Properties of Laminated Core Specimen UsingVoltmeter-
to 20000 Hz) under sinusoidal flux conditions.
Ammeter-Wattmeter Methods
1.3 This test method, because of the use of a feedback-
A801Specification for Wrought Iron-Cobalt High Magnetic
controlled power amplifier, is well suited for determination of
Saturation Alloys (UNS R30005 and K92650)
ac magnetic properties at magnetic flux densities above the
knee of the magnetization curve and is particularly useful for
3. Significance and Use
testing of high-saturation iron-cobalt alloys (for example,
3.1 This test method is a derivative of Test Method A697/
alloys listed in Specification A801), although use of this test
A697M specifically designed for testing of toroidal cores
method is not restricted to a particular type of material.
which are not covered in Test Method A697/A697M and for
1.4 This test method shall be used in conjunction with
testing at magnetic flux densities above the knee of the
Practice A34/A34M and Terminology A340.
magnetization curve.
1.5 The values stated in either SI units or inch-pound units
3.2 Specimen size typically ranges from 1in. to 1.25 in.
are to be regarded separately as standard. The values stated in
[25.4mm to 31.8 mm] in inside diameter to 1.5 in. [38.1 mm]
each system may not be exact equivalents; therefore, each
in outside diameter with weights ranging from 30g to 60 g.
system shall be used independently of the other. Combining
Provided the test equipment is suitably chosen, there is no
values from the two systems may result in non-conformance
obvious limit to the overall size of core that can be tested. If
with the standard.
basic material properties are desired, then the requirements of
1.6 This standard does not purport to address all of the
5.1 must be observed.
safety concerns, if any, associated with its use. It is the
3.3 The reproducibility and repeatability of this test method
responsibility of the user of this standard to establish appro-
are such that this test method is suitable for design, specifica-
priate safety, health, and environmental practices and deter-
tion acceptance, service evaluation, and research and develop-
mine the applicability of regulatory limitations prior to use.
ment.
1.7 This international standard was developed in accor-
3.4 When testing under sinusoidal flux conditions at mag-
dance with internationally recognized principles on standard-
netic flux densities approaching saturation, highly peaked
ization established in the Decision on Principles for the
magnetizing waveforms will be present, and the test instru-
Development of International Standards, Guides and Recom-
ments used must have crest factor capabilities of at least 3;
mendations issued by the World Trade Organization Technical
otherwise erroneous results will be obtained.
Barriers to Trade (TBT) Committee.
This test method is under the jurisdiction ofASTM Committee A06 and is 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, 2022. Published November 2022. Originally contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM
approved in 1994. Last previous edition approved in 2018 as A927/A927M–18. Standards volume information, refer to the standard’s Document Summary page on
DOI: 10.1520/A0927_A0927M-18R22. the ASTM website.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
A927/A927M − 18 (2022)
4. Apparatus current and rms voltage to an accuracy of 60.5% or better;
otherwise, separate instruments meeting this accuracy require-
4.1 The apparatus for testing under this test method shall
ment must be used.
consist of as many of the components, described below and
schematically illustrated in Fig. 1, as required to perform the 4.5 Flux Voltmeter—The flux voltmeter must be a true
measurements. average responding, high-impedance voltmeter calibrated to
read =2 π/4 times the full wave rectified average voltage so
4.2 Signal Generator—For testing at other than line fre-
that its indications will be identical to those of a true rms
quency (50Hz or 60 Hz), a low distortion sine wave signal
voltmeter when reading a pure sinusoidal voltage. The rated
generator is required. The frequency accuracy of the signal
full-scale accuracy must be 60.5% or better.
generator should be within 60.1%. To prevent dc biasing of
the magnetizing current waveform, a blocking capacitor or
4.6 Current-Sensing Resistor (Optional)—When peak per-
isolation transformer should be installed between the signal
meability is to be measured, a noninductive, high-precision,
generator and power amplifier.
low-thermal coefficient of resistance current-sensing resistor
shallbeused.Theresistormustberatedtocarrythemaximum
4.3 Power Amplifier—A linear power amplifier should be
current used in the test.
used (see Note 1). The signal from the secondary winding of
the test specimen is used for negative feedback control of the
4.7 Peak Voltmeter (Optional)—When peak permeability is
magnetizing waveform. Depending on the power amplifier
to be determined, a high-impedance peak-reading voltmeter
used, it may be necessary to install feedback signal condition-
shall be used to measure the voltage drop across the current-
ing equipment such as an attenuator or amplifier; however, the
sensing resistor.The voltmeter must have a full-scale accuracy
signal conditioning equipment must not distort the feedback
of 61% or better, a crest factor of at least 3, and appropriate
waveform nor load the secondary winding. Fig. 1 also shows
bandwidth.
an audio choke connecting the output and feedback terminals
4.8 Oscilloscope (Optional)—An oscilloscope displaying
oftheamplifier.Thischokeisintendedtopreventdcbiasbeing
both the magnetizing current waveform and secondary voltage
introduced into the magnetizing waveform by providing dc
permitstheoperatortoobservethewaveforms.Thisisparticu-
feedback to the power amplifier. Without such a choke, the dc
larly useful when setting up the test for the first time. The
offset current present in certain power amplifiers will result in
oscilloscope must have a very high input impedance to avoid
large dc output currents. This choke may not be needed
loading of the secondary winding.
depending on the make and model of power supply. Further
reduction or elimination of bias can be achieved by installing
5. Test Specimen
an isolation transformer to transformer couple the primary
5.1 The test specimen must be either a stack of toroidal
circuit.
(washer ring) laminations formed by punching, machining, or
NOTE 1—Audio amplifiers are suitable in some instances, although the etching or a toroidal tape wound core. For measurement of
smallspecimencrosssectionandtherelativelyfewprimaryturnstypically
basicmaterialproperties,theratioofinsidetooutsidediameter
used results in a low Q circuit and, therefore, difficulty in maintaining
must be 0.82 or greater.
sinusoidal flux at magnetic flux densities approaching saturation. In
addition, an impedance matchingtransformermayberequiredtoimprove
6. Procedure
power transfer.
6.1 The test specimen should be heat treated after fabrica-
4.4 Wattmeter—An electronic wattmeter with appropriate
tion.Bentorotherwisedamagedlaminationsortapecoresshall
voltage, current and wattage ranges, and bandwidth must be
be discarded.
used. The full-scale accuracy of the wattmeter must be better
6.2 The core shall be weighed to an accuracy of 60.1% or
than 60.5%.Thewattmetermusthaveacrestfactorcapability
of at least 3 and be capable of accurate measurements at better and the inside and outside diameters measured to an
accuracy of 0.1% or better.
low-powerfactors.Thewattmetermustbeabletomeasurerms
6.3 The laminations or tape core should be enclosed in a
rigid, nonconductive case (core box) or placed in a suitable
fixture to avoid winding stresses. The test core should fill the
core box or fixture as fully as possible to minimize air flux.
6.4 Primary and secondary windings, N and N , are ap-
1 2
plied; the secondary winding should be applied first. Both
windings should be uniformly wound over the circumference
of the toroid. The secondary winding may use finer diameter
wire than the primary winding, which should be of sufficient
diameter to carry the magnetizing current without overheating.
Al
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