ASTM A348/A348M-00
(Test Method)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
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
SCOPE
1.1 This test method covers the determination of the magnetic properties of flat-rolled magnetic materials using Epstein test specimens with double-lap joints in the 25-cm Epstein frame. It covers determination of core loss, rms and peak exciting current, exciting power, magnetic field strength, and permeability. This test method is commonly used to test grain-oriented and nonoriented electrical steels but may also be used to test nickel-iron, cobalt-iron, and other flat-rolled magnetic materials.
1.2 This test method shall be used in conjunction with Practice A34/A34M and Test Method A343.
1.3 Tests under this test method may be conducted with either normal ac magnetization or with ac magnetization and superimposed dc bias (incremental magnetization).
1.4 In general, this test method has the following limitations:
1.4.1 Frequency--The range of this test method normally covers frequencies from 100 to 10 000 Hz. With proper equipment, the test method may be extended above 10 000 Hz. When tests are limited to the use of power sources having frequencies below 100 Hz, they shall use the procedures of Test Method A343.
1.4.2 Magnetic Induction(may also be referred to as Induction)--The range of induction for this test method is governed by the test specimen properties and by the available instruments and other equipment components. Normally, for many materials, the induction range is from 1 to 15 kG [0.1 to 1.5 T].
1.4.3 Core Loss and Exciting Power--These measurements are normally limited to test conditions that do not cause a test specimen temperature rise in excess of 50oC or exceed 100 W/lb [220 W/kg].
1.4.4 Excitation--Either rms or peak values of exciting current may be measured at any test point that does not exceed the equipment limitations provided that the impedance of the ammeter shunt is low and its insertion into the test circuit does not cause appreciably increased voltage waveform distortion at the test induction.
1.4.5 Incremental Properties--Measurement of incremental properties shall be limited to combinations of ac and dc excitations that do not cause secondary voltage waveform distortion, as determined by the form factor method, to exceed a shift of 10 % away from sine wave conditions.
1.5 The values and equations stated in either customary (cgs-emu and inch-pound) or SI units are to be regarded separately as standard. Within this standard, SI units are shown in brackets except for the sections concerning calculations where there are separate sections for the respective unit systems. 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.
1.6 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 and health practices and determine the applicability of regulatory limitations prior to use.
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Designation:A 348/A348M–00
Standard Test Method for
Alternating Current Magnetic Properties of Materials Using
the Wattmeter-Ammeter-Voltmeter Method, 100 to 10000 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 (e) indicates an editorial change since the last revision or reapproval.
1. Scope the equipment limitations provided that the impedance of the
ammeter shunt is low and its insertion into the test circuit does
1.1 This test method covers the determination of the mag-
notcauseappreciablyincreasedvoltagewaveformdistortionat
netic properties of flat-rolled magnetic materials using Epstein
the test induction.
test specimens with double-lap joints in the 25-cm Epstein
1.4.5 Incremental Properties—Measurement of incremental
frame. It covers determination of core loss, rms and peak
properties shall be limited to combinations of ac and dc
exciting current, exciting power, magnetic field strength, and
excitations that do not cause secondary voltage waveform
permeability. This test method is commonly used to test
distortion, as determined by the form factor method, to exceed
grain-orientedandnonorientedelectricalsteelsbutmayalsobe
a shift of 10% away from sine wave conditions.
used to test nickel-iron, cobalt-iron, and other flat-rolled
1.5 The values and equations stated in either customary
magnetic materials.
(cgs-emu and inch-pound) or SI units are to be regarded
1.2 This test method shall be used in conjunction with
separatelyasstandard.Withinthisstandard,SIunitsareshown
Practice A34/A34M and Test Method A343.
in brackets except for the sections concerning calculations
1.3 Tests under this test method may be conducted with
where there are separate sections for the respective unit
either normal ac magnetization or with ac magnetization and
systems. The values stated in each system may not be exact
superimposed dc bias (incremental magnetization).
equivalents;therefore,eachsystemshallbeusedindependently
1.4 In general, this test method has the following limita-
of the other. Combining values from the two systems may
tions:
result in nonconformance with this standard.
1.4.1 Frequency—The range of this test method normally
1.6 This standard does not purport to address all of the
covers frequencies from 100 to 10000 Hz. With proper
safety concerns, if any, associated with its use. It is the
equipment, the test method may be extended above 10000 Hz.
responsibility of the user of this standard to establish appro-
When tests are limited to the use of power sources having
priate safety and health practices and determine the applica-
frequenciesbelow100Hz,theyshallusetheproceduresofTest
bility of regulatory limitations prior to use.
Method A343.
1.4.2 Magnetic Induction (may also be referred to as
2. Referenced Documents
Induction)—The range of induction for this test method is
2.1 ASTM Standards:
governed by the test specimen properties and by the available
A34/A34M PracticeforSamplingandProcurementTesting
instruments and other equipment components. Normally, for
of Magnetic Materials
many materials, the induction range is from 1 to 15 kG [0.1 to
A340 Terminology of Symbols and Definitions Relating to
1.5 T].
Magnetic Testing
1.4.3 Core Loss and Exciting Power—These measurements
A343 Test Method forAlternating-Current Magnetic Prop-
are normally limited to test conditions that do not cause a test
erties of Materials at Power Frequencies UsingWattmeter-
specimen temperature rise in excess of 50°C or exceed 100
Ammeter-Voltmeter Method and 25-cm Epstein Test
W/lb [220 W/kg].
Frame
1.4.4 Excitation—Either rms or peak values of exciting
A347 Test Method forAlternating Current Magnetic Prop-
current may be measured at any test point that does not exceed
erties of Materials Using the Dieterly Bridge Method with
25-cm Epstein Frame
This test method is under the jurisdiction of ASTM Committee A06 on
MagneticPropertiesandisthedirectresponsibilityofSubcommitteeA06.01onTest
Methods.
Current edition approved Oct. 10, 2000. Published December 2000. Originally Annual Book of ASTM Standards, Vol 03.04.
published as A348–60T. Last previous edition A348/A348M–95a. Discontinued, see 1995 Annual Book of ASTM Standards, Vol 03.04.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.
A 348/A348M–00
TABLE 1 Number of Strips for Various Nominal Specimen
3. Summary of Test Method
Weight Epstein Frames (Minimum Strip Length is 28 cm [280
3.1 A representative sample of the magnetic material is cut
mm])
into Epstein strips and then annealed or otherwise treated in
Number of Strips for Test Specimens of
Nominal Strip Thickness
accordance with the appropriate material specification or as
Nominal Weight
agreed between producer and user. The strips are weighed and
Thick (cm) Thick (in.) 125 g 250 g 500 g 1000 g
loaded into the Epstein frame becoming the transformer core.
0.079 0.0310 . . 12 20
The primary coil is then excited with ac voltage and current at
0.071 0.0280 . . 12 24
0.064 0.0250 . . 12 24
the frequencies and inductions of interest and measurements
0.056 0.0220 . . 16 28
taken. In some cases, a dc magnetic field strength is superim-
0.047 0.0185 . 12 16 32
posed (incremental dc bias).The magnetic parameters are then
0.043 0.0170 . 12 20 36
0.039 0.0155 . 12 20 40
calculated from the data.
0.036 0.0140 . 12 24 44
0.032 0.0125 . 12 24 48
4. Significance and Use
0.028 0.0110 . 16 28 56
0.025 0.0100 . 16 32 60
4.1 Thistestmethodevaluatestheperformanceofflat-rolled
0.023 0.0090 . 16 36 68
magnetic materials over a wide frequency range of ac excita-
0.020 0.0080 12 20 40 76
tion with and without incremental dc bias, as used on trans-
0.018 0.0070 12 24 44 88
A
0.015 0.0060 12 24 52
formers, motors, and other laminated core devices.
A
0.013 0.0050 16 32 60
4.2 This test method is suitable for design, specification
A
0.010 0.0040 20 40 76
AA
acceptance, service evaluation, and research.
0.0076 0.0030 24 52
AA
0.0051 0.0020 40 76
4.3 The application of test results obtained with this test
AAA
0.0025 0.0010 76
method to the design or evaluation of a particular magnetic
A
Not recommended.
device must recognize the influence of the magnetic circuitry
uponitsperformance.Somespecificitemstoconsideraresize,
shape, holes, welding, staking, bolting, bracketing, shorting
driving the test circuit with an ac sinusoidal waveform voltage
between laminations, ac waveform, adjacent magnetic fields,
of desired amplitude and frequency. The series resistance
and stress.
components,randwattmetercurrentshunt,inconjunctionwith
the ac source, shall be such as to provide a pure sine wave
5. Test Specimens
voltage either at the test frame transformer primary, or if
5.1 The test specimens shall consist of Epstein strips cut
overall negative feedback is implemented, then the pure sine
from sheets or coiled strips of magnetic materials in accor-
wave shall be at the test frame transformer secondary. The
dance with the test lot and sampling requirements of Practice
wiring and switches shall be selected to minimize current or
A34/A34M, Sections 5 and 7, andTest MethodA343,Annex
voltage reading errors, for example, the voltage connections
A3 (see Note 1).
acrossrshallbemadepreciselyattheresistorterminalssothat
NOTE 1—Excessiveburrandnonflatnessofstripscanappreciablyaffect no wire resistance is effectively added to that of the resistor.
test results.
Also, all voltage reading or negative feedback components
across the secondary of the test frame transformer shall cause
5.1.1 If specimen is primarily isotropic, cut one half of the
negligible loading, that is, shall draw sufficiently low currents
stripswithgrainandone-halfcrossgrain.Ifanisotropic,cutall
to not appreciably affect power or current readings. When a
with grain. Other ratios of with and cross grain may be chosen
common ground connection is made between primary and
by agreement.
secondary of the test frame transformer, the ac source ground
5.2 The test specimen shall consist of multiples of four
connection must be isolated to eliminate ground loop current.
strips. The total number of strips shall be such as to:
5.2.1 Provide sufficient total losses to register within the
7. Apparatus
range of required accuracy of the wattmeter.
7.1 The test apparatus shall consist of as many of the
5.2.2 Fill the available vertical opening space in the test
frame to at least ⁄4 of its maximum height and following components as required to perform the desired
5.2.3 Contain a minimum of twelve strips. measurement functions:
5.3 Check each strip to assure its length and width are 7.2 Balance or Scale—the balance or scales used for deter-
accurate to 60.04 cm [0.4 mm]. If the length is not 30.5 cm mining the mass of the test specimen shall weigh to an
[305 mm], use the actual length as described in Sections 9 and accuracy of 0.05%. The calculated test voltage E is directly
f
10. If the width is not 3.0 cm [30 mm], check that all strips are proportional to specimen mass and induction. Errors in induc-
the same width within 0.04 cm [0.4 mm]. tion can cause disproportionately greater errors in the core loss
5.4 Table 1 shows the number of Epstein strips that will and exciting current.
provide nominal weights of approximately 125, 250, 500, and 7.3 Epstein Test Frame:
1000 g for various strip thicknesses. 7.3.1 Thedimensionsofthewindings,theirspacing,andthe
general precautions and construction details of Test Method
6. Basic Circuit (see Fig. 1)
A343,AnnexA1,shallapply.TheEpsteintestframeshouldbe
6.1 Fig. 1 shows the essential apparatus and basic circuit selected to be compatible with the desired test specimen size
connections for this test. The ac source shall be capable of (see 5.4).
A 348/A348M–00
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
7.3.2 The following numbers of total winding turns are restricted to moderate induction and field strength where test
usually commercially available and are suggested for testing at specimen relative permeability remains high, the difference
various frequencies: between B and B is small and air flux compensation is
i
unnecessary.
Frequency, Hz No. of Turns (Both Primary and Secondary)
7.4 Flux Voltmeter—A full wave true average responsive
Up to 400 700 or 352
voltmeter calibrated so that its scale reads true average3p
400 to 1000 352
2/4,andindicatesthesamevalueasanrmsvoltmeterwhen
1000 to 5000 200 (no air-flux compensator) =
5000 to 10 000 100 (no air-flux compensator)
measuring pure sine waves, shall be provided for measuring
the peak value of the test induction. To meet the precision of
7.3.3 The primary winding is uniformly distributed along
this test method, meter error shall not exceed 0.25% (see Note
the magnetic path and may be wound in multiple layers over
2). If the meter impedance is not sufficiently high at the
the secondary winding. The secondary winding shall be the
frequency of test, it is necessary to compensate for its loading
innermost winding on the coil form and shall be a single layer
effect. To evaluate how much the meter loads the circuit, read
winding. The primary and secondary shall be wound in the
the rms ammeter and rms voltmeter before and after discon-
samedirectionandtheirstartingendconnectionsshallbemade
necting the flux voltmeter. When dc bias is applied to the test
at the same corner.
frame transformer, the flux voltmeter must be able to respond
7.3.4 Air Flux Compensator—If the Epstein test frame has
true average.
more than 200 turns, it shall contain an air flux compensator
which opposes and balances out the air flux voltage induced in
NOTE 2—Inaccuracies in setting the test voltage produce errors dispro-
the secondary winding. Such compensation is necessary when-
portionately larger in core loss and exciting current. Evaluate meter error
in accordance with the manufacturer’s information, for example, percent
ever the permeability of the test specimen is low under high
of range, temperature, and frequency.
magnetic field strength conditions to avoid serious errors in
setting the flux voltage. The air flux compensator allows the 7.5 RMSVoltmeter—ARMSvoltmetershallbeprovidedfor
true intrinsic induction B to be measured. When tests are evaluating the exciting power and also the form factor of the
i
A 348/A348M–00
voltage induced in the secondary winding of the test frame loscope also makes it possible to recognize current waveform
transformer. The meter error shall not exceed 0.25% at the nonsymmetry with positive and negative polarity. Such non-
frequency of test. The meter burden shall have no more than symmetry results when a dc component is present along with
0.05% effect on the test frame transformer voltage or current. the ac in the primary winding of the test frame, causing
To evaluate how much the meter loads the circuit, read the nonsymmetrical B versus H excitation. This condition causes
RMS ammeter and flux voltmeter before and after disconnect- serious peak current reading errors. Temporarily inverting the
ing the RMS voltmeter. When dc bias is applied to the test waveform by flipping the oscilloscope“ invert” switch is an
frametransformer,theRMSmetermustbeabletoindicatetrue effective way to observe waveform symmetry. Some oscillo-
RMS ac voltage. scopeshaveaprovisionforautomaticallyanddigitallydisplay-
ing the peak of a waveform and thus may be used to read the
7.6 Oscilloscope Voltage Monitor (Optional)—An oscillo-
peak current instead of a peak reading voltmeter. An oscillo-
scope may be provided to monitor the waveshape of the
scope, when used, shall not cause unwanted shorting of any
secondary voltage. Connection of the oscilloscope shall not
part in the circuit through its dual input ground.
affect the voltage
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