ASTM A348/A348M-05(2021)

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: A348/A348M − 05 (Reapproved 2021)
Standard Test Method for
Alternating Current Magnetic Properties of Materials Using
the Wattmeter-Ammeter-Voltmeter Method, 100 to 10 000 Hz
and 25-cm Epstein Frame
This standard is issued under the fixed designationA348/A348M; 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 1.4.4 Excitation—Either rms or peak values of exciting
current may be measured at any test point that does not exceed
1.1 This test method covers the determination of the mag-
the equipment limitations provided that the impedance of the
netic properties of flat-rolled magnetic materials using Epstein
ammeter shunt is low and its insertion into the test circuit does
test specimens with double-lap joints in the 25-cm Epstein
notcauseappreciablyincreasedvoltagewaveformdistortionat
frame. It covers determination of core loss, rms and peak
the test magnetic flux density.
exciting current, exciting power, magnetic field strength, and
1.4.5 Incremental Properties—Measurement of incremental
permeability. This test method is commonly used to test
properties shall be limited to combinations of ac and dc
grain-orientedandnonorientedelectricalsteelsbutmayalsobe
excitations that do not cause secondary voltage waveform
used to test nickel-iron, cobalt-iron, and other flat-rolled
distortion, as determined by the form factor method, to exceed
magnetic materials.
a shift of 10% away from sine wave conditions.
1.2 This test method shall be used in conjunction with
1.5 The values and equations stated in customary (cgs-emu
Practice A34/A34M and Test Method A343/A343M.
and inch-pound) or SI units are to be regarded separately as
1.3 Tests under this test method may be conducted with
standard. Within this standard, SI units are shown in brackets
either normal ac magnetization or with ac magnetization and
except for the sections concerning calculations where there are
superimposed dc bias (incremental magnetization).
separate sections for the respective unit systems. The values
1.4 In general, this test method has the following limita- stated in each system may not be exact equivalents; therefore,
each system shall be used independently of the other. Combin-
tions:
1.4.1 Frequency—The range of this test method normally ingvaluesfromthetwosystemsmayresultinnonconformance
covers frequencies from 100 to 10000 Hz. With proper with this standard.
equipment,thetestmethodmaybeextendedabove10000Hz.
1.6 This standard does not purport to address all of the
When tests are limited to the use of power sources having
safety concerns, if any, associated with its use. It is the
frequenciesbelow100Hz,theyshallusetheproceduresofTest
responsibility of the user of this standard to establish appro-
Method A343/A343M.
priate safety, health, and environmental practices and deter-
1.4.2 Magnetic Flux Density (may also be referred to as
mine the applicability of regulatory limitations prior to use.
Flux Density)—Therangeofmagneticfluxdensityforthistest
1.7 This international standard was developed in accor-
method is governed by the test specimen properties and by the
dance with internationally recognized principles on standard-
available instruments and other equipment components.
ization established in the Decision on Principles for the
Normally, for many materials, the magnetic flux density range
Development of International Standards, Guides and Recom-
is from 1 to 15 kG [0.1 to 1.5 T].
mendations issued by the World Trade Organization Technical
1.4.3 Core Loss and Exciting Power—These measurements
Barriers to Trade (TBT) Committee.
are normally limited to test conditions that do not cause a test
2. Referenced Documents
specimen temperature rise in excess of 50°C or exceed 100
W/lb [220 W/kg].
2.1 ASTM Standards:
A34/A34MPractice for Sampling and Procurement Testing
of Magnetic Materials
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 June 1, 2021. Published June 2021. Originally contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM
approved in 1960. Last previous edition approved in 2015 as A348/A348M–05 Standards volume information, refer to the standard’s Document Summary page on
(2015). DOI: 10.1520/A0348_A0348M-05R21. the ASTM website.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
A348/A348M − 05 (2021)
A340Terminology of Symbols and Definitions Relating to 5.4 Table 1 shows the number of Epstein strips that will
Magnetic Testing provide nominal weights of approximately 125, 250, 500, and
A343/A343MTest Method for Alternating-Current Mag- 1000 g for various strip thicknesses.
netic Properties of Materials at Power Frequencies Using
6. Basic Circuit (see Fig. 1)
Wattmeter-Ammeter-Voltmeter Method and 25-cm Ep-
stein Test Frame
6.1 Fig. 1 shows the essential apparatus and basic circuit
connections for this test. The ac source shall be capable of
3. Summary of Test Method
driving the test circuit with an ac sinusoidal waveform voltage
3.1 A representative sample of the magnetic material is cut
of desired amplitude and frequency. The series resistance
into Epstein strips and then annealed or otherwise treated in
components, randwattmetercurrentshunt,inconjunctionwith
accordance with the appropriate material specification or as
the ac source, shall be such as to provide a pure sine wave
agreed between producer and user. The strips are weighed and
voltage either at the test frame transformer primary, or if
loaded into the Epstein frame becoming the transformer core.
overall negative feedback is implemented, then the pure sine
The primary coil is then excited with ac voltage and current at
wave shall be at the test frame transformer secondary. The
the frequencies and magnetic flux densities of interest and
wiring and switches shall be selected to minimize current or
measurements taken. In some cases, a dc magnetic field
voltage reading errors, for example, the voltage connections
strength is superimposed (incremental dc bias). The magnetic
across rshallbemadepreciselyattheresistorterminalssothat
parameters are then calculated from the data.
no wire resistance is effectively added to that of the resistor.
Also, all voltage reading or negative feedback components
4. Significance and Use
across the secondary of the test frame transformer shall cause
4.1 Thistestmethodevaluatestheperformanceofflat-rolled
negligible loading, that is, shall draw sufficiently low currents
magnetic materials over a wide frequency range of ac excita-
to not appreciably affect power or current readings. When a
tion with and without incremental dc bias, as used on
common ground connection is made between primary and
transformers, motors, and other laminated core devices.
secondary of the test frame transformer, the ac source ground
connection must be isolated to eliminate ground loop current.
4.2 This test method is suitable for design, specification
acceptance, service evaluation, and research.
7. Apparatus
4.3 The application of test results obtained with this test
7.1 The test apparatus shall consist of as many of the
method to the design or evaluation of a particular magnetic
following components as required to perform the desired
device must recognize the influence of the magnetic circuitry
measurement functions:
uponitsperformance.Somespecificitemstoconsideraresize,
7.2 Balance or Scale—The balance or scales used for
shape, holes, welding, staking, bolting, bracketing, shorting
determining the mass of the test specimen shall weigh to an
between laminations, ac waveform, adjacent magnetic fields,
accuracy of 0.05%. The calculated test voltage E is directly
and stress.
f
proportional to specimen mass and magnetic flux density (see
5. Test Specimens
Note 2).
5.1 The test specimens shall consist of Epstein strips cut
from sheets or coiled strips of magnetic materials in accor-
TABLE 1 Number of Strips for Various Nominal Specimen Weight
dance with the test lot and sampling requirements of Practice
Epstein Frames (Minimum Strip Length is 28 cm [280 mm])
A34/A34M, Sections 5 and 7, and Test Method A343/A343M,
Number of Strips for Test Specimens of
Nominal Strip Thickness
Annex A3 (see Note 1).
Nominal Weight
Thick (cm) Thick (in.) 125 g 250 g 500 g 1000 g
NOTE1—Excessiveburrandnonflatnessofstripscanappreciablyaffect
0.079 0.0310 . . 12 20
test results.
0.071 0.0280 . . 12 24
5.1.1 If specimen is primarily isotropic, cut one half of the
0.064 0.0250 . . 12 24
0.056 0.0220 . . 16 28
stripswithgrainandone-halfcrossgrain.Ifanisotropic,cutall
0.047 0.0185 . 12 16 32
with grain. Other ratios of with and cross grain may be chosen
0.043 0.0170 . 12 20 36
by agreement.
0.039 0.0155 . 12 20 40
0.036 0.0140 . 12 24 44
5.2 The test specimen shall consist of multiples of four
0.032 0.0125 . 12 24 48
strips. The total number of strips shall be such as to: 0.028 0.0110 . 16 28 56
0.025 0.0100 . 16 32 60
5.2.1 Provide sufficient total losses to register within the
0.023 0.0090 . 16 36 68
range of required accuracy of the wattmeter.
0.020 0.0080 12 20 40 76
5.2.2 Fill the available vertical opening space in the test
0.018 0.0070 12 24 44 88
A
1 0.015 0.0060 12 24 52
frame to at least ⁄4 of its maximum height and
A
0.013 0.0050 16 32 60
5.2.3 Contain a minimum of twelve strips. A
0.010 0.0040 20 40 76
AA
0.0076 0.0030 24 52
5.3 Check each strip to assure its length and width are
AA
0.0051 0.0020 40 76
AAA
accurate to 60.04 cm [0.4 mm]. If the length is not 30.5 cm
0.0025 0.0010 76
[305 mm], use the actual length as described in Sections 9 and A
Not recommended.
10.
A348/A348M − 05 (2021)
NOTE 1—The ac source terminals must “float” to prevent ground loop currents. If the wattmeter has a common connection between its V and I
terminals, the rest of the circuit must be connected so as to prevent shorting.
NOTE 2—If, during demagnetization, current exceeds the wattmeter maximum rating, Switch S1 is required and is closed.
NOTE 3—A dc winding is required only if incremental properties are to be tested.
NOTE 4—The voltage and current monitoring oscilloscope may be a dual channel type and is optional equipment. Basic circuit-wattmeter-ammeter-
voltmeter method, 100 to 10000 Hz and 25-cm Epstein frame
FIG. 1 Basic Circuit-Wattmeter-Ammeter-Voltmeter Method, 100 to 10 000 Hz and 25–cm Epstein Frame
NOTE 2—Errors in the weight of a specimen will cause errors in 7.3.4 Air Flux Compensator—If the Epstein test frame has
magnetic flux density, core loss, and exciting power.
more than 200 turns, it shall contain an air flux compensator
7.3 Epstein Test Frame:
which opposes and balances out the air flux voltage induced in
7.3.1 Thedimensionsofthewindings,theirspacing,andthe
the secondary winding. Such compensation is necessary when-
general precautions and construction details of Test Method
ever the permeability of the test specimen is low under high
A343/A343M, Annex A1, shall apply. The Epstein test frame
magnetic field strength conditions to avoid serious errors in
should be selected to be compatible with the desired test
setting the flux voltage. The air flux compensator allows the
specimen size (see 5.4).
true intrinsic induction B to be measured. When tests are
i
7.3.2 The following numbers of total winding turns are
restricted to moderate magnetic flux density and field strength
usually commercially available and are suggested for testing at
where test specimen relative permeability remains high, the
various frequencies:
difference between B and B is small and air flux compensation
i
Frequency, Hz No. of Turns (Both Primary and Secondary)
is unnecessary.
Up to 400 700 or 352
7.4 Flux Voltmeter—A full wave true average responsive
400 to 1000 352
voltmeter calibrated so that its scale reads true average
1000 to 5000 200 (no air-flux compensator)
5000 to 10 000 100 (no air-flux compensator) 3π =2/4, and indicates the same value as an rms voltmeter
when measuring pure sine waves, shall be provided for
7.3.3 The primary winding is uniformly distributed along
measuring the peak value of the test induction. To meet the
the magnetic path and may be wound in multiple layers over
precision of this test method, meter error shall not exceed
the secondary winding. The secondary winding shall be the
0.25% (see Note 3). If the meter impedance is not sufficiently
innermost winding on the coil form and shall be a single layer
winding. The primary and secondary shall be wound in the high at the frequency of test, it is necessary to compensate for
its loading effect. To evaluate how much the meter loads the
samedirectionandtheirstartingendconnectionsshallbemade
at the same corner. circuit, read the rms ammeter and rms voltmeter before and
A348/A348M − 05 (2021)
after disconnecting the flux voltmeter. When dc bias is applied across the terminals of the current sensing resistor (r in Fig. 1)
tothetestframetransformer,thefluxvoltmetermustbeableto shall be provided to measure the peak value of the current
respond true average. waveform. Accuracy shall be 2%. Alternatively, an oscillo-
NOTE 3—Inaccuracies in setting the test voltage produce errors dispro- scope with voltage measurement capability can be used. An
portionately larger in core loss and exciting current. Evaluate meter error
oscilloscope,whenused,shallnotcauseshortingofanypartof
in accordance with the manufacturer’s information, for example, percent
the circuit through its dual input common ground.
of range, temperature, and frequency.
7.10 Oscilloscope Current Monitor (Optional)—Extreme
7.5 RMS Voltmeter—ARMSvoltmetershallbeprovidedfor
current wave peaking occurs as the magnetic core material
evaluating the exciting power and also the form factor of the
goes into saturation. This is readily observable on an oscillo-
voltage induced in the secondary winding of the test frame
scope connected across the current sensing resistor. An oscil-
transformer. The meter error shall not exceed 0.25% at the
loscope also makes it possible to recognize current waveform
frequency of test. The meter burden shall have no more than
nonsymmetry with positive and negative polarity. Such non-
0.05% effect on the test frame transformer voltage or current.
symmetry results when a dc component is present along with
To evaluate how much the meter loads the circuit, read the
the ac in the primary winding of the test frame, causing
RMS ammeter and flux voltmeter before and after disconnect-
nonsymmetrical B versus H excitation. This condition causes
ing the RMS voltmeter. When dc bias is applied to the test
serious peak current reading errors. Temporarily inverting the
frametransformer,theRMSmetermustbeabletoindicatetrue
waveform by flipping the oscilloscope “invert” switch is an
RMS ac voltage.
effective way to observe waveform symmetry. Some oscillo-
7.6 Oscilloscope Voltage Monitor (Optional)—An oscillo-
scopeshaveaprovisionforautomaticallyanddigitallydisplay-
scope may be provided to monitor the waveshape of the
ing the peak of a waveform and thus may be used to read the
secondary voltage. Connection of the oscilloscope shall not
peak current instead of a peak reading voltmeter. An
affect the voltage or current more than 0.05%.
oscilloscope, when used, shall not cause unwanted shorting of
7.6.1 The oscilloscope dual input common ground connec- any part in the circuit through its dual input ground.
tions shall not cause ground loop currents in any part of the
7.11 ac Source(seeFig.2)—Apreciselycontrollablesource
circuit.
of sinusoidal test voltage characterized by low internal
impedance, low harmonic distortion (1%), excellent voltage
7.7 Wattmeter—The wattmeter error shall not exceed
stability (0.1%), and excellent frequency stability (0.1%) is
0.25% at unity power factor at the frequency of test. Error
required.
shall not exceed 1% of reading at the lowest power factor
7.11.1 The ac source shall be ac coupled to prevent dc bias
encountered. If desired, the reactive power may also be
in the test fixture transformer. The ac source would typically
measured or calculated.
consist of some or all of the following components:
7.7.1 The voltage sensing terminals of the wattmeter shall
7.11.1.1 Sine Wave Generator.
have an input impedance sufficiently high that the voltage or
7.11.1.2 Power Amplifier.
current is changed no more than 0.05%.
7.11.1.3 Isolation Transformer or Coupling Capacitor.
7.7.2 The current sensing terminals of the wattmeter shall
7.11.1.4 Impedance Matching Tapped Transformer or Auto-
have a low impedance so as to not change the test fixture
transformer.
transformer primary current waveshape appreciably. An input
7.11.2 Sine Wave Generator—A sinusoidal wave generator
impedance of 0.1 Ω is preferred. The wattmeter shall be
orsynthesizercapableofgeneratingthesignaldescribedabove
capable of accepting the maximum peak current encountered
shall be provided. This signal is input to the power amplifier.
without exceeding its crest factor rating.
7.11.3 Power Amplifier—An amplifier of voltage and cur-
7.8 RMS Ammeter—A RMS ammeter consisting of a RMS
rent to be fed to the test frame transformer shall be provided.
voltmeterconnectedacrosstheterminalsofthecurrentsensing
It shall be capable of amplifying the signal while maintaining
resistor (rin Fig. 1) shall be provided. The RMS voltmeter
the waveform and meeting specifications described above. It
shall have an error no greater than 0.25% considering the
may use negative feedback to meet the low source impedance
maximum crest factor and all frequencies and amplitudes
and low waveform distortion requirements. It may consist, for
encountered in the measurement. Connection to the circuit
example, of an audio amplifier with several hundred watts
shall not cause appreciable changes in voltage or waveform.
The current sensing resistor shall be accurate to 0.1% and be
essentially noninductive at the frequency of test. It shall have
a power rating several times the maximum power to be
experienced during the test. Voltmeter connections to the
resistor shall be made precisely at the resistor terminals so that
wire resistance does not add to the known resistor value and
cause error.The resistor value shall be 0.1Ω or, if higher, shall
not cause a voltage drop greater than 5% of the test frame
voltage.
7.9 Peak Ammeter—Atrue peak, or peak-to-peak, ammeter
consisting of a true peak or peak-to-peak voltmeter connected FIG. 2 Circuit Diagram of Typical ac Source
A348/A348M − 05 (2021)
rating. If it is a dc-coupled amplifier, an ac isolation trans- voltageslowlyandprogressivelyduringanelapsedtimeof5to
former or capacitor shown in Fig. 2 is required. 10 s (or longer) so that the flux density is reduced smoothly to
7.11.4 Isolation Transformer—The isolation transformer, if a point below the lowest flux density at which tests are to be
required,shallhavesufficientbandwidth,coupling,andpower- performed and near zero flux density. Demagnetization to near
handling capacity to maintain signal integrity and low source zero magnetic flux density is especially critical when measur-
impedance, even with dc offset of a dc coupled amplifier ing properties at very low flux density (for example, 100 G).
feeding it. Its output shall be routed to the test frame trans- After demagnetization, take care not to jar or move the
former primary. specimen in any way that will destroy the desired reproducible
7.11.5 Coupling Capacitor—The coupling capacitors, magneticstateofnegligiblemagneticfluxdensity.Testsshould
which are an alternate to the isolation transformer, shall be a bemadeimmediatelyafterdemagnetization(within2to3min)
pair of electrolytic capacitors connected back to back with for the desired test points using the following sequence of
sufficient effective capacitance to maintain the low source testing:
impedance of the power amplifier. Alternatively, an ac-rated 8.4.1 Begin the tests at the lowest test magnetic flux density
capacitor may be used. andtestinorderofincreasingmaximummagneticfluxdensity.
7.11.6 Impedance Matching Tapped Transformer or Do not overshoot the target magnetic flux density level
Autotransformer—Atransformer or autotransformer with fixed appreciably, especially at low magnetic flux densities.
or variable taps shall be provided if necessary to match the 8.4.2 When frequency is varied at constant magnetic flux
power amplifier source impedance to that of the test frame density,beginthetestsatthelowestfrequencyandtestinorder
transformer. It shall have bandwidth and power-handling of increasing frequency.
capacity to maintain signal integrity. If this is a transformer 8.4.3 Repeat the demagnetization before determining a test
with isolated primary and secondary windings, the isolation pointateitheralowermagneticfluxdensityorlowerfrequency
transformer or coupling capacitor mentioned above may be than that of the previous test point.
omitted.
8.5 Meter Readings—Once the magnetic flux density level
is correct and steady, proceed to record the following:
8. Procedure
E = flux voltage (secondary),
8.1 Check the specimen strips to assure that no dented,
f
E = rms voltage (secondary),
twisted, or distorted strips showing evidence of mechanical
W = core wattage,
abusehavebeenincluded.Stripshavingreadilynoticeableburr
P = core volt-amperes reactive (optional),
q
(greater than 0.0005 in. [0.02 mm]) may also be unsuitable for
I = rms exciting current (primary), or
testing. Verify that the strips are of uniform length and width
E = rms voltage across r,
r
and that the appropriate number of strips with the appropriate
I = peak exciting current (primary), or
p
grain direction are available (see Table 1). Weigh strips on a
E = peak voltage across r,or
pr
scale or balance capable of determining the mass to within
I = peak-to-peak exciting current (primary), or
p-p
60.05%.
E = peak-to-peak voltage across r,
p-pr
f = frequency (if more than one frequency), and
8.2 Calculate Magnetic Flux Density—Calculate and record
r = shunt resistance.
the flux voltage values corresponding to all the magnetic flux
NOTE 5—Voltages E and E may also be observed or measured or
pr p-pr
density levels to be tested (see Sections9 and 10).Adata sheet
both with an oscilloscope. Gather information on test frame transformer
form should be prepared with spaces to enter every required
secondary voltmeter and wattmeter burdens and record them so correc-
meter reading and other data (see Note 4).
tionscanbemadeifnecessary,thatis,iftheyaffectaccuracybymorethan
0.1%.
NOTE 4—The calculations may be performed and a data sheet printout
obtained by use of a computer appropriately programmed. Use of data
8.6 Increme
...