ASTM A596/A596M-95(2004)e1
(Test Method)Standard Test Method for Direct-Current Magnetic Properties of Materials Using the Ballistic Method and Ring Specimens
Standard Test Method for Direct-Current Magnetic Properties of Materials Using the Ballistic Method and Ring Specimens
SIGNIFICANCE AND USE
Test methods using suitable ring-type specimens are the preferred methods of determining the basic magnetic properties of a material caused by the absence of demagnetizing effects and are well suited for specification acceptance, service evaluation, and research and development.
Provided the test specimen is representative of the bulk material as is usually the case for thin strip and wire, this test is also suitable for design purposes.
When the test specimen is not necessarily representative of the bulk material such as a ring machined from a large forging or casting, the results of this test method may not be an accurate indicator of the magnetic properties of the bulk material. In such instances, the test results when viewed in context of past performance history will be useful for judging the suitability of the current material for the intended application.
SCOPE
1.1 This test method covers dc ballistic testing for the determination of basic magnetic properties of materials in the form of ring, toroidal, link, double-lapped Epstein cores, or other standard shapes which may be cut, stamped, machined, or ground from cast, compacted, sintered, forged, or rolled materials. It includes tests for normal induction and hysteresis taken under conditions of steep wavefront reversals of the direct-current magnetic field strength.
1.2 This test method shall be used in conjunction with Practice A 34/A 34M.
1.3 This test method is suitable for a testing range from very low magnetic field strength up to 200 or more Oe [15.9 or more kA/m]. The lower limit is determined by integrator sensitivity and the upper limit by heat generation in the magnetizing winding. Special techniques and short duration testing may extend the upper limit of magnetic field strength.
1.4 Testing under this test method is inherently more accurate than other methods. When specified dimensional or shape requirements are observed, the measurements are a good approximation to absolute properties. Test accuracy available is primarily limited by the accuracy of instrumentation.
1.5 This test method permits a choice of test specimen to permit measurement of properties in any desired direction relative to the direction of crystallographic orientation without interference from external yoke systems.
1.6 The symbols and abbreviated definitions used in this test method appear in Fig. 1 and Sections 5, 6, 9, and 10. For the official definitions see Terminology A 340. Note that the term flux density used in this document is synonymous with the term magnetic induction.
1.7 Warning—Mercury has been designated by EPA and many state agencies as a hazardous material that can cause central nervous system, kidney, and liver damage. Mercury, or its vapor, may be hazardous to health and corrosive to materials. Caution should be taken when handling mercury and mercury-containing products. See the applicable product Material Safety Data Sheet (MSDS) for details and EPA’s website (http://www.epa.gov/mercury/faq.htm) for additional information. Users should be aware that selling mercury or mercury-containing products, or both, in your state may be prohibited by state law.
1.8 The values stated in either customary (cgs-emu and inch-pound) units or SI units are to be regarded separately as standard. Within this test method, the 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 are not exact equivalents; therefore, each system shall be used independently of the other. Combining values from the two systems may result in nonconformance with this method.
1.9 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 li...
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´1
Designation:A596/A596M–95 (Reapproved 2004)
Standard Test Method for
Direct-Current Magnetic Properties of Materials Using the
Ballistic Method and Ring Specimens
This standard is issued under the fixed designationA596/A596M; 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.
´ NOTE—Mercury warning was editorially added in January 2009.
1. Scope materials.Cautionshouldbetakenwhenhandlingmercuryand
mercury-containing products. See the applicable product Ma-
1.1 This test method covers dc ballistic testing for the
terial Safety Data Sheet (MSDS) for details and EPA’s website
determination of basic magnetic properties of materials in the
(http://www.epa.gov/mercury/faq.htm) for additional informa-
form of ring, toroidal, link, double-lapped Epstein cores, or
tion. Users should be aware that selling mercury or mercury-
other standard shapes which may be cut, stamped, machined,
containingproducts,orboth,inyourstatemaybeprohibitedby
or ground from cast, compacted, sintered, forged, or rolled
state law.
materials. It includes tests for normal induction and hysteresis
1.8 The values stated in either customary (cgs-emu and
taken under conditions of steep wavefront reversals of the
inch-pound) units or SI units are to be regarded separately as
direct-current magnetic field strength.
standard. Within this test method, the SI units are shown in
1.2 This test method shall be used in conjunction with
brackets except for the sections concerning calculations where
Practice A34/A34M.
there are separate sections for the respective unit systems. The
1.3 Thistestmethodissuitableforatestingrangefromvery
values stated in each system are not exact equivalents; there-
lowmagneticfieldstrengthupto200ormoreOe[15.9ormore
fore, each system shall be used independently of the other.
kA/m]. The lower limit is determined by integrator sensitivity
Combiningvaluesfromthetwosystemsmayresultinnoncon-
and the upper limit by heat generation in the magnetizing
formance with this method.
winding. Special techniques and short duration testing may
1.9 This standard does not purport to address all of the
extend the upper limit of magnetic field strength.
safety concerns, if any, associated with its use. It is the
1.4 Testing under this test method is inherently more accu-
responsibility of the user of this standard to establish appro-
rate than other methods. When specified dimensional or shape
priate safety and health practices and determine the applica-
requirements are observed, the measurements are a good
bility of regulatory limitations prior to use.
approximationtoabsoluteproperties.Testaccuracyavailableis
primarily limited by the accuracy of instrumentation.
2. Referenced Documents
1.5 This test method permits a choice of test specimen to
2.1 ASTM Standards:
permit measurement of properties in any desired direction
A34/A34M Practice for Sampling and Procurement Testing
relative to the direction of crystallographic orientation without
of Magnetic Materials
interference from external yoke systems.
A340 Terminology of Symbols and Definitions Relating to
1.6 Thesymbolsandabbreviateddefinitionsusedinthistest
Magnetic Testing
method appear in Fig. 1 and Sections 5, 6, 9, and 10. For the
A341/A341M Test Method for Direct Current Magnetic
official definitions see Terminology A340. Note that the term
Properties of Materials Using D-C Permeameters and the
fluxdensityusedinthisdocumentissynonymouswiththeterm
Ballistic Test Methods
magnetic induction.
A343/A343M Test Method for Alternating-Current Mag-
1.7 Warning—Mercury has been designated by EPA and
netic Properties of Materials at Power Frequencies Using
many state agencies as a hazardous material that can cause
Wattmeter-Ammeter-VoltmeterMethodand25-cmEpstein
central nervous system, kidney, and liver damage. Mercury, or
Test Frame
its vapor, may be hazardous to health and corrosive to
A773/A773M Test Method for dc Magnetic Properties of
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 Oct. 1, 2004. Published October 2004. Originally contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM
approved in 1969. Last previous edition approved in 1999 as A596/A596–95 Standards volume information, refer to the standard’s Document Summary page on
(1999). DOI: 10.1520/A0596_A0596M-95R04E01. the ASTM website.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.
´1
A596/A596M–95 (2004)
4. Interferences
4.1 This test method has several important requirements.
Unless adequate inside diameter to outside diameter ratios are
maintained in the test specimens, the magnetic field strength
will be excessively nonuniform throughout the test specimen
andthemeasuredparameterscannotberepresentedasmaterial
properties.
4.2 The basic quality of materials having directionally
sensitivepropertiescannotbetestedsatisfactorilywithringsor
laminations. With them it is necessary to use Epstein speci-
mens cut with their lengths in the direction of specific interest
or to use long link-shaped or spirally wound toroidal core test
specimens whose long dimensions are similarly located. The
acceptableminimumwidthofstripusedinsuchtestspecimens
is also sensitive to the material under test. At present, it is
believed that the grain-oriented silicon steels should have a
NOTE 1— strip width of at least 3 cm [30 mm].
A —Multirange ammeter, main-magnetizing current circuit
1 4.3 Unlessringspecimensarelargeindiameter,itisdifficult
A —Multirange ammeter, hysteresis-current circuit
toprovideasufficientnumberofprimaryturnsneededtoreach
N —Magnetizing (primary) winding
the highest magnetic field strength. In general, magnetic
N —Flux-sensing (secondary) winding
materials tend to have nonuniform properties throughout the
F—Electronic integrator
body of the test specimen; for this reason, uniformly distrib-
R —Main current control rheostat
R —Hysteresis current control rheostat
uted test windings and uniform specimen cross-sectional area
S —Reversing switch
1 are highly desirable to suppress nonuniform behavior to a
S —Shunting switch for hysteresis current control rheostat
tolerable degree.
FIG. 1 Basic Circuit Using Ring-Type Cores
5. Apparatus
5.1 The apparatus shall consist of as many of the compo-
Materials Using Ring and Permeameter Procedures with
nents described in 5.2-5.10 as are required to perform the
dc Electronic Hysteresigraphs
desired test. The basic circuit is shown in Fig. 1.
2.2 IEC Standard:
5.2 Balance and Scales:
Publication 404-4, Magnetic Materials—Part 4: Methods of
5.2.1 The balance used to weigh the test specimen shall be
Measurement of the D-C Magnetic Properties of Solid
capable of weighing to an accuracy of better than 0.1%.
Steels, IEC, 1982
5.2.2 The micrometer, caliper, or other length-measuring
device used in the determination of magnetic path length and
3. Significance and Use
cross-sectional area shall be capable of measuring to an
3.1 Test methods using suitable ring-type specimens are
accuracy of better than 0.1%.
the preferred methods of determining the basic magnetic
5.3 dc Power Supply—The preferred source of dc current is
properties of a material caused by the absence of demagnetiz-
a high quality linear power supply of either unipolar or bipolar
ing effects and are well suited for specification acceptance,
operation. The power supply must exhibit high stability and
service evaluation, and research and development.
very low ripple to achieve the most accurate results. Program-
3.2 Provided the test specimen is representative of the bulk
mable bipolar operational amplifier power supplies have
material as is usually the case for thin strip and wire, this test
proven to be very satisfactory for this type of testing. Other
is also suitable for design purposes.
stable sources of dc current such as storage batteries are
3.3 Whenthetestspecimenisnotnecessarilyrepresentative
permitted.
of the bulk material such as a ring machined from a large
5.4 Main-Current-Control Rheostat R —When nonpro-
forgingorcasting,theresultsofthistestmethodmaynotbean
grammable sources of dc current such as storage batteries are
accurate indicator of the magnetic properties of the bulk
used, rheostats must be used to control the current. These
material. In such instances, the test results when viewed in
rheostatsmusthavesufficientpowerratingandheat-dissipating
context of past performance history will be useful for judging
capabilitytohandlethelargesttestcurrentwithoutundesirable
the suitability of the current material for the intended applica-
changes in resistance and, therefore, magnetizing current
tion.
during conduct of the test.
5.5 Hysteresis-Current-Control Rheostat R —The
hysteresis-current-control rheostat, when required, must have
Available fromAmerican National Standards Institute (ANSI), 25 W. 43rd St.,
the same power rating and resistance as the main-current-
4th Floor, New York, NY 10036.
control rheostat.
Lloyd, M. G., “Errors in Magnetic Testing with Ring Specimens,’’ Technical
5.6 Main-Current Ammeter A —Measurement of the mag-
News Bulletin, National Institute for Standards andTechnology,Vol 5, 1909, p. 435 1
(S108). netizing current can be accomplished with either a dc ammeter
´1
A596/A596M–95 (2004)
oracombinationofaprecisionshuntresistoranddcvoltmeter. testresultsshouldnotberepresentedasmaterialpropertiesbut
The meters and shunt resistor, if used, must have an accuracy should be called core properties because of nonuniform flux
of at least 0.25%. To improve test accuracy multirange digital distribution.
ammeters or voltmeters are preferred. Autoranging capability 6.3 When link, oval-shaped, or rectangular test specimen
is desirable for convenience but is not essential for this test forms are used, the requirements of 6.2 apply to the end or
method.Ifanalogmetersareused,therangesmustbesuchthat corner sections where flux crowding occurs. When straight-
all test readings are made in the upper two thirds of the scale. sided test specimens are very long relative to the length of the
corner or end sections, they are suitable for basic material
5.7 Hysteresis-Current Ammeter, A —The hysteresis-
properties evaluation with relatively unoriented materials pro-
current measuring system shall conform to the requirements in
vided the uncertainty in determination of true-path (effective)
5.6. In general, a separate measuring system is not required
length is less than 5% of the total path length. When this
since the main current ammeter (A ) can also be used to
uncertainty in path length (shortest or longest relative to the
measure the hysteresis current.
mean-path length) exceeds 5%, the test values should be
5.8 Reversing Switch, S —Because of the low resistance
reported as core properties and not basic material properties.
nature of the magnetizing circuit, it is imperative that high
6.4 Thetestspecimenmaybeconstructedofsolidlaminated
quality switches be used. Changes in switch resistance upon
or strip materials and in any of the shapes described in 1.1.
reversal will cause deviation from the cyclically magnetized
6.5 Test specimen cores made from strip may be laminated,
condition which, if excessive, will impair test accuracy and
machined, spirally wound, or Epstein specimens (the method
precision. Experience has shown that mercury switches are the
of selection for Epstein specimens is described inTest Method
best suited for this application. Knife blade switches or
A343/A343M,Appendix 3). When the material is to be tested
mechanical or electrically operated contractors can also be
half transverse and half longitudinal, the material shall be cut
used provided the requirement for uniform and equal contact
into Epstein strips or square laminations of adequate dimen-
resistance can be maintained. Because of the presence of
sional ratio.
leakagecurrentsintheopencondition,solidstaterelaysarenot
6.6 Test specimens used for basic material evaluation shall
permitted. The difficulties inherent in the use of main current
be cut, machined, ground, slit, or otherwise formed to have a
reversing switches can be minimized by use of linear power
cross section that remains sufficiently uniform that its nonuni-
supplies capable of accepting a remote programming signal.
formity will not materially affect the accuracy of establishing
Such power supplies are permitted provided that the magne-
andmeasuringfluxdensity, B,ormagneticfieldstrength, H,in
tizingcurrentisequal(towithin0.1%)ineitherpolaritywhen
the test specimen.
normal induction testing is conducted, current reversals can be
6.7 When required for material properties development, the
conductedwithnoovershootoroscillationandthemagnetizing
test specimen shall have received a stress relief or other heat
current is truly zero for the zero current programming signal.
treatment after preparation. This heat treatment is subject to
5.9 Hysteresis Switch, S (When Required)—This switch
agreementbetweenmanufacturerandpurchaser,manufacturers
should conform to requirements in 5.8.
recommendation,ortherecommendedheattreatmentprovided
5.10 Integrator, F—Because of their superior accuracy,
by the appropriate ASTM standard for the material. The heat
stability, and ease of operation, electronic charge integrators
treatment used shall be reported with the magnetic test results.
are the preferred means of measuring magnetic flux. Integra-
tors using either operational amplifier and capacitor feedback
7. Calibration of Integrator
(analog integrator) or pulse counting are permitted. The accu-
7.1 Practical operating experience has shown that provided
racy of the integrator must be better than 1% full scale. If
a proper warmup period is allowed, electronic integrators
analog display meters are used to read the value of flux, the
require infrequent calibration and unlike ballistic galvanom-
measurement should be made on the upper two thirds of the
eters, calibration is not an integral part of this test method.
scale. Analog integrators must have drift adjust circuitry and
When calibration is required, it can be accomplished with
−6
thedriftshouldnotexceed100Maxwell-turns[10 Wb-turns]
either a mutual inductor or a volt-second source. Because of
per minute on the most sensitive range. It is also de
...
This document is not anASTM standard and is intended only to provide the user of anASTM standard an indication of what changes have been made to the previous version. Because
it may not be technically possible to adequately depict all changes accurately,ASTM recommends that users consult prior editions as appropriate. In all cases only the current version
of the standard as published by ASTM is to be considered the official document.
´1
Designation: A 596/A 596M – 95 (Reapproved 2004)
Standard Test Method for
Direct-Current Magnetic Properties of Materials Using the
Ballistic Method and Ring Specimens
ThisstandardisissuedunderthefixeddesignationA596/A596M;thenumberimmediatelyfollowingthedesignationindicatestheyear
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.
´ NOTE—Mercury warning was editorially added in January 2009.
1. Scope
1.1 This test method covers dc ballistic testing for the determination of basic magnetic properties of materials in the form of
ring, toroidal, link, double-lapped Epstein cores, or other standard shapes which may be cut, stamped, machined, or ground from
cast, compacted, sintered, forged, or rolled materials. It includes tests for normal induction and hysteresis taken under conditions
of steep wavefront reversals of the direct-current magnetic field strength.
1.2 This test method shall be used in conjunction with Practice A34/A34M.
1.3 This test method is suitable for a testing range from very low magnetic field strength up to 200 or more Oe [15.9 or more
kA/m].The lower limit is determined by integrator sensitivity and the upper limit by heat generation in the magnetizing winding.
Special techniques and short duration testing may extend the upper limit of magnetic field strength.
1.4 Testing under this test method is inherently more accurate than other methods. When specified dimensional or shape
requirementsareobserved,themeasurementsareagoodapproximationtoabsoluteproperties.Testaccuracyavailableisprimarily
limited by the accuracy of instrumentation.
1.5 This test method permits a choice of test specimen to permit measurement of properties in any desired direction relative to
the direction of crystallographic orientation without interference from external yoke systems.
1.6 ThesymbolsandabbreviateddefinitionsusedinthistestmethodappearinFig.1andSections5,6,9,and10.Fortheofficial
definitions see TerminologyA340. Note that the term flux density used in this document is synonymous with the term magnetic
induction.
1.7The values stated in either customary (cgs-emu and inch-pound) units or SI units are to be regarded separately as standard.
Withinthistestmethod,theSIunitsareshowninbracketsexceptforthesectionsconcerningcalculationswherethereareseparate
sections for the respective unit systems. The values stated in each system are not exact equivalents; therefore, each system shall
be used independently of the other. Combining values from the two systems may result in nonconformance with this method.
1.8
1.7 Warning—Mercury has been designated by EPA and many state agencies as a hazardous material that can cause central
nervous system, kidney, and liver damage. Mercury, or its vapor, may be hazardous to health and corrosive to materials. Caution
should be taken when handling mercury and mercury-containing products. See the applicable product Material Safety Data Sheet
(MSDS) for details and EPA’s website ( http://www.epa.gov/mercury/faq.htm) for additional information. Users should be aware
that selling mercury or mercury-containing products, or both, in your state may be prohibited by state law.
1.8 The values stated in either customary (cgs-emu and inch-pound) units or SI units are to be regarded separately as standard.
Withinthistestmethod,theSIunitsareshowninbracketsexceptforthesectionsconcerningcalculationswherethereareseparate
sections for the respective unit systems. The values stated in each system are not exact equivalents; therefore, each system shall
be used independently of the other. Combining values from the two systems may result in nonconformance with this method.
1.9 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.
2. Referenced Documents
2.1 ASTM Standards:
A34/A34M Practice for Sampling and Procurement Testing of Magnetic Materials
This test method is under the jurisdiction ofASTM CommitteeA06 on Magnetic Properties and is the direct responsibility of SubcommitteeA06.01 on Test Methods.
Current edition approved Oct. 1, 2004. Published October 2004. Originally approved in 1969. Last previous edition approved in 1999 as A596/A596–95 (1999).
ForreferencedASTMstandards,visittheASTMwebsite,www.astm.org,orcontactASTMCustomerServiceatservice@astm.org.For Annual Book of ASTM Standards
volume information, refer to the standard’s Document Summary page on the ASTM website.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.
´1
A 596/A 596M – 95 (2004)
NOTE 1—
A —Multirange ammeter, main-magnetizing current circuit
A —Multirange ammeter, hysteresis-current circuit
N —Magnetizing (primary) winding
N —Flux-sensing (secondary) winding
F—Electronic integrator
R —Main current control rheostat
R —Hysteresis current control rheostat
S —Reversing switch
S —Shunting switch for hysteresis current control rheostat
FIG. 1 Basic Circuit Using Ring-Type Cores
A340 Terminology of Symbols and Definitions Relating to Magnetic Testing
A341/A341M TestMethodforDirectCurrentMagneticPropertiesofMaterialsUsingdcPermeametersandtheBallisticTest
Methods
A343/A343M Test Method for Alternating-Current Magnetic Properties of Materials at Power Frequencies Using the
Wattmeter-Ammeter-Voltmeter Method and 25-cm Epstein Test Frame
A773/A773M Test Method for dc Magnetic Properties of Materials Using Ring and Permeameter Procedures with dc
Electronic Hysteresigraphs
2.2 IEC Standard:
Publication404-4, MagneticMaterials—Part4:MethodsofMeasurementoftheD-CMagneticPropertiesofSolidSteels,IEC,
3. Significance and Use
3.1 Test methods using suitable ring-type specimens are the preferred methods of determining the basic magnetic properties
of a material caused by the absence of demagnetizing effects and are well suited for specification acceptance, service evaluation,
and research and development.
3.2 Provided the test specimen is representative of the bulk material as is usually the case for thin strip and wire, this test is
also suitable for design purposes.
3.3 When the test specimen is not necessarily representative of the bulk material such as a ring machined from a large forging
or casting, the results of this test method may not be an accurate indicator of the magnetic properties of the bulk material. In such
instances,thetestresultswhenviewedincontextofpastperformancehistorywillbeusefulforjudgingthesuitabilityofthecurrent
material for the intended application.
4. Interferences
4.1 This test method has several important requirements. Unless adequate inside diameter to outside diameter ratios are
maintained in the test specimens, the magnetic field strength will be excessively nonuniform throughout the test specimen and the
measured parameters cannot be represented as material properties.
4.2 The basic quality of materials having directionally sensitive properties cannot be tested satisfactorily with rings or
laminations.With them it is necessary to use Epstein specimens cut with their lengths in the direction of specific interest or to use
Available from American National Standards Institute (ANSI), 25 W. 43rd St., 4th Floor, New York, NY 10036.
Lloyd,M.G.,“ErrorsinMagneticTestingwithRingSpecimens,’’ Technical News Bulletin,NationalInstituteforStandardsandTechnology,Vol5,1909,p.435(S108).
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A 596/A 596M – 95 (2004)
long link-shaped or spirally wound toroidal core test specimens whose long dimensions are similarly located. The acceptable
minimum width of strip used in such test specimens is also sensitive to the material under test.At present, it is believed that the
grain-oriented silicon steels should have a strip width of at least 3 cm [30 mm].
4.3 Unless ring specimens are large in diameter, it is difficult to provide a sufficient number of primary turns needed to reach
the highest magnetic field strength. In general, magnetic materials tend to have nonuniform properties throughout the body of the
test specimen; for this reason, uniformly distributed test windings and uniform specimen cross-sectional area are highly desirable
to suppress nonuniform behavior to a tolerable degree.
5. Apparatus
5.1 The apparatus shall consist of as many of the components described in 5.2-5.10 as are required to perform the desired test.
The basic circuit is shown in Fig. 1.
5.2 Balance and Scales:
5.2.1 The balance used to weigh the test specimen shall be capable of weighing to an accuracy of better than 0.1%.
5.2.2 The micrometer, caliper, or other length-measuring device used in the determination of magnetic path length and
cross-sectional area shall be capable of measuring to an accuracy of better than 0.1%.
5.3 dc Power Supply—The preferred source of dc current is a high quality linear power supply of either unipolar or bipolar
operation. The power supply must exhibit high stability and very low ripple to achieve the most accurate results. Programmable
bipolar operational amplifier power supplies have proven to be very satisfactory for this type of testing. Other stable sources of
dc current such as storage batteries are permitted.
5.4 Main-Current-Control Rheostat R —When nonprogrammable sources of dc current such as storage batteries are used,
rheostats must be used to control the current. These rheostats must have sufficient power rating and heat-dissipating capability to
handle the largest test current without undesirable changes in resistance and, therefore, magnetizing current during conduct of the
test.
5.5 Hysteresis-Current-Control Rheostat R —Thehysteresis-current-controlrheostat,whenrequired,musthavethesamepower
rating and resistance as the main-current-control rheostat.
5.6 Main-Current Ammeter A — Measurement of the magnetizing current can be accomplished with either a dc ammeter or a
combinationofaprecisionshuntresistoranddcvoltmeter.Themetersandshuntresistor,ifused,musthaveanaccuracyofatleast
0.25%.To improve test accuracy multirange digital ammeters or voltmeters are preferred.Autoranging capability is desirable for
convenience but is not essential for this test method. If analog meters are used, the ranges must be such that all test readings are
made in the upper two thirds of the scale.
5.7 Hysteresis-Current Ammeter, A —The hysteresis-current measuring system shall conform to the requirements in 5.6. In
general,aseparatemeasuringsystemisnotrequiredsincethemaincurrentammeter(A )canalsobeusedtomeasurethehysteresis
current.
5.8 Reversing Switch, S — Because of the low resistance nature of the magnetizing circuit, it is imperative that high quality
switchesbeused.Changesinswitchresistanceuponreversalwillcausedeviationfromthecyclicallymagnetizedconditionwhich,
if excessive, will impair test accuracy and precision. Experience has shown that mercury switches are the best suited for this
application. Knife blade switches or mechanical or electrically operated contractors can also be used provided the requirement for
uniform and equal contact resistance can be maintained. Because of the presence of leakage currents in the open condition, solid
state relays are not permitted. The difficulties inherent in the use of main current reversing switches can be minimized by use of
linear power supplies capable of accepting a remote programming signal. Such power supplies are permitted provided that the
magnetizing current is equal (to within 0.1%) in either polarity when normal induction testing is conducted, current reversals can
be conducted with no overshoot or oscillation and the magnetizing current is truly zero for the zero current programming signal.
5.9 Hysteresis Switch, S (When Required) —This switch should conform to requirements in 5.8.
5.10 Integrator, F—Because of their superior accuracy, stability, and ease of operation, electronic charge integrators are the
preferred means of measuring magnetic flux. Integrators using either operational amplifier and capacitor feedback (analog
integrator) or pulse counting are permitted. The accuracy of the integrator must be better than 1% full scale. If analog display
metersareusedtoreadthevalueofflux,themeasurementshouldbemadeontheuppertwothirdsofthescale.Analogintegrators
−6
musthavedriftadjustcircuitryandthedriftshouldnotexceed100Maxwell-turns[10 Wb-turns]perminuteonthemostsensitive
range. It is also desirable that the integrator have appropriate scaling circuitry to permit direct reading of either flux (f)orflux
density(B).Ballisticgalvanometersormovingcoilfluxmetersareallowedprovidedthe1%full-scaleaccuracyrequirementismet.
6. Test Specimen
6.1 When the test specimen represents a test lot of material, its selection shall conform to the requirements of Practice
A34/A34M or of an individual specification.
6.2 To qualify as a test specimen suitable for evaluation of material properties the effective ratio of mean diameter to radial
width shall be not less than 10 to 1 (or an inside diameter to outside diameter ratio not less than 0.82). When the test specimen
hassmallerratiosthantheaboverequirements,thetestresultsshouldnotberepresentedasmaterialpropertiesbutshouldbecalled
core properties because of nonuniform flux distribution.
6.3 When link, oval-shaped, or rectangular test specimen forms are used, the requirements of 6.2 apply to the end or corner
´1
A 596/A 596M – 95 (2004)
sections where flux crowding occurs. When straight-sided test specimens are very long relative to the length of the corner or end
sections, they are suitable for basic material properties evaluation with relatively unoriented materials provided the uncertainty in
determinationoftrue-path(effective)lengthislessthan5%ofthetotalpathlength.Whenthisuncertaintyinpathlength(shortest
orlongestrelativetothemean-pathlength)exceeds5%,thetestvaluesshouldbereportedascorepropertiesandnotbasicmaterial
properties.
6.4 The test specimen may be constructed of solid laminated or strip materials and in any of the shapes described in 1.1.
6.5 Test specimen cores made from strip may be laminated, machined, spirally wound, or Epstein spe
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