1、Designation: A927/A927M 11A927/A927M 18Standard Test Method forAlternating-Current Magnetic Properties of Toroidal CoreSpecimens Using the Voltmeter-Ammeter-WattmeterMethod1This standard is issued under the fixed designation A927/A927M; the number immediately following the designation indicates the
2、yearof original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval.A superscript epsilon () indicates an editorial change since the last revision or reapproval.1. Scope1.1 This test method covers the determination of several
3、 ac magnetic properties of either laminated ring or toroidal tape woundcores made from flat rolled product.1.2 This test method covers test equipment and procedures for determination of specific core loss, specific exciting power, andpeak permeability for power and audio frequencies (50 to 20 000 Hz
4、) under sinusoidal flux conditions.1.3 This test method, because of the use of a feedback-controlled power amplifier, is well suited for determination of acmagnetic properties at magnetic flux densities above the knee of the magnetization curve and is particularly useful for testing ofhigh-saturatio
5、n iron-cobalt alloys (for example, alloys listed in Specification A801), although use of this test method is notrestricted to a particular type of material.1.4 This test method shall be used in conjunction with Practice A34/A34M and Terminology A340.1.5 The values stated in either SI units or inch-p
6、ound units are to be regarded separately as standard. The values stated in eachsystem may not be exact equivalents; therefore, each system shall be used independently of the other. Combining values from thetwo systems may result in non-conformance with the standard.1.6 This standard does not purport
7、 to address all of the safety concerns, if any, associated with its use. It is the responsibilityof the user of this standard to establish appropriate safety safety, health, and healthenvironmental practices and determine theapplicability of regulatory limitations prior to use.1.7 This international
8、 standard was developed in accordance with internationally recognized principles on standardizationestablished in the Decision on Principles for the Development of International Standards, Guides and Recommendations issuedby the World Trade Organization Technical Barriers to Trade (TBT) Committee.2.
9、 Referenced Documents2.1 ASTM Standards:2A34/A34M Practice for Sampling and Procurement Testing of Magnetic MaterialsA340 Terminology of Symbols and Definitions Relating to Magnetic TestingA697/A697M Test Method for Alternating Current Magnetic Properties of Laminated Core Specimen Using Voltmeter-A
10、mmeter-Wattmeter MethodsA801 Specification for Wrought Iron-Cobalt High Magnetic Saturation Alloys (UNS R30005 and K92650)3. Significance and Use3.1 This test method is a derivative of Test Method A697/A697M specifically designed for testing of toroidal cores which arenot covered in Test Method A697
11、/A697M and for testing at magnetic flux densities above the knee of the magnetization curve.3.2 Specimen size typically ranges from 1 to 1.25 in. 25.4 to 31.8 mm in inside diameter to 1.5 in. 38.1 mm in outsidediameter with weights ranging from 30 to 60 g. Provided the test equipment is suitably cho
12、sen, there is no obvious limit to theoverall size of core that can be tested. If basic material properties are desired, then the requirements of 5.1 must be observed.1 This test method is under the jurisdiction of ASTM Committee A06 and is the direct responsibility of Subcommittee A06.01 on Test Met
13、hods.Current edition approved Aug. 1, 2011May 1, 2018. Published August 2011May 2018. Originally approved in 1994. Last previous edition approved in 20042011 asA927/A927MA927/A927M 11.04. DOI: 10.1520/A0927_A0927M-11.10.1520/A0927_A0927M-18.2 For referencedASTM standards, visit theASTM website, www.
14、astm.org, or contactASTM Customer Service at serviceastm.org. For Annual Book of ASTM Standardsvolume information, refer to the standards Document Summary page on the ASTM website.This document is not an ASTM standard and is intended only to provide the user of an ASTM standard an indication of what
15、 changes have been made to the previous version. Becauseit 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 versionof the standard as published by ASTM is to be considered the
16、official document.Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States13.3 The reproducibility and repeatability of this test method are such that this test method is suitable for design, specificationacceptance, service evaluation, and re
17、search and development.3.4 When testing under sinusoidal flux conditions at magnetic flux densities approaching saturation, highly peaked magnetizingwaveforms will be present, and the test instruments used must have crest factor capabilities of at least 3; otherwise erroneousresults will be obtained
18、.4. Apparatus4.1 The apparatus for testing under this test method shall consist of as many of the components, described below andschematically illustrated in Fig. 1, as required to perform the measurements.4.2 Signal GeneratorFor testing at other than line frequency (50 or 60 Hz), a low distortion s
19、ine wave signal generator isrequired. The frequency accuracy of the signal generator should be within 60.1 %. To prevent dc biasing of the magnetizingcurrent waveform, a blocking capacitor or isolation transformer should be installed between the signal generator and poweramplifier.4.3 Power Amplifie
20、rA linear power amplifier should be used (see Note 1). The signal from the secondary winding of the testspecimen is used for negative feedback control of the magnetizing waveform. Depending on the power amplifier used, it may benecessary to install feedback signal conditioning equipment such as an a
21、ttenuator or amplifier; however, the signal conditioningequipment must not distort the feedback waveform nor load the secondary winding. Fig. 1 also shows an audio choke connectingthe output and feedback terminals of the amplifier. This choke is intended to prevent dc bias being introduced into the
22、magnetizingwaveform by providing dc feedback to the power amplifier. Without such a choke, the dc offset current present in certain poweramplifiers will result in large dc output currents. This choke may not be needed depending on the make and model of power supply.Further reduction or elimination o
23、f bias can be achieved by installing an isolation transformer to transformer couple the primarycircuit.NOTE 1Audio amplifiers are suitable in some instances, although the small specimen cross section and the relatively few primary turns typically usedresults in a low Q circuit and, therefore, diffic
24、ulty in maintaining sinusoidal flux at magnetic flux densities approaching saturation. In addition, animpedance matching transformer may be required to improve power transfer.4.4 WattmeterAn electronic wattmeter with appropriate voltage, current and wattage ranges, and bandwidth must be used. Theful
25、l-scale accuracy of the wattmeter must be better than 60.5 %. The wattmeter must have a crest factor capability of at least 3and be capable of accurate measurements at low-power factors.The wattmeter must be able to measure rms current and rms voltageto an accuracy of 60.5 % or better; otherwise, se
26、parate instruments meeting this accuracy requirement must be used.4.5 Flux VoltmeterThe flux voltmeter must be a true average responding, high-impedance voltmeter calibrated to read=2 pi/4times the full wave rectified average voltage so that its indications will be identical to those of a true rms v
27、oltmeter when readinga pure sinusoidal voltage. The rated full-scale accuracy must be 60.5 % or better.4.6 Current-Sensing Resistor (Optional)When peak permeability is to be measured, a noninductive, high-precision,low-thermal coefficient of resistance current-sensing resistor shall be used.The resi
28、stor must be rated to carry the maximum currentused in the test.4.7 Peak Voltmeter (Optional)When peak permeability is to be determined, a high-impedance peak-reading voltmeter shallbe used to measure the voltage drop across the current-sensing resistor. The voltmeter must have a full-scale accuracy
29、 of 61 %or better, a crest factor of at least 3, and appropriate bandwidth.4.8 Oscilloscope (Optional)An oscilloscope displaying both the magnetizing current waveform and secondary voltagepermits the operator to observe the waveforms. This is particularly useful when setting up the test for the firs
30、t time. Theoscilloscope must have a very high input impedance to avoid loading of the secondary winding.FIG. 1 Schematic Illustration of Test ApparatusA927/A927M 1825. Test Specimen5.1 The test specimen must be either a stack of toroidal (washer ring) laminations formed by punching, machining, or et
31、chingor a toroidal tape wound core. For measurement of basic material properties, the ratio of inside to outside diameter must be 0.82or greater.6. Procedure6.1 The test specimen should be heat treated after fabrication. Bent or otherwise damaged laminations or tape cores shall bediscarded.6.2 The c
32、ore shall be weighed to an accuracy of 60.1 % or better and the inside and outside diameters measured to an accuracyof 0.1 % or better.6.3 The laminations or tape core should be enclosed in a rigid, nonconductive case (core box) or placed in a suitable fixture toavoid winding stresses. The test core
33、 should fill the core box or fixture as fully as possible to minimize air flux.6.4 Primary and secondary windings, N1 and N2, are applied; the secondary winding should be applied first. Both windingsshould be uniformly wound over the circumference of the toroid. The secondary winding may use finer d
34、iameter wire than theprimary winding, which should be of sufficient diameter to carry the magnetizing current without overheating. Alternately, afabricated magnetizing fixture may be used provided the windings are uniformly distributed over the length of the core.6.5 If the number of turns on the se
35、condary winding is not equal to the number of turns on the primary winding, additionalcircuitry such as amplifiers or attenuators may be required to control the “loop gain” in the waveform feedback loop. Failure tocontrol the “loop gain” will normally result in power supply instability.6.6 The flux
36、voltage, Ef, induced in the secondary winding, N2, at the required magnetic flux density, B,m, shall be computedusing the equation found in 7.2 or 8.2.6.7 The test specimen is connected to the test apparatus and demagnetized. Demagnetization must be done by smoothlyreducing the magnetizing current s
37、tarting from a magnetic flux density above the knee of the magnetization curve and at the testfrequency.6.8 The magnetizing current is increased to obtain the flux voltage corresponding to the lowest required magnetic flux density.6.9 The form factor of the secondary voltage is computed by dividing
38、the rms secondary voltage by the flux voltage. The formfactor must be within 61 % of the value for a sine wave for testing conducted in accordance with this test method. Once testconditions have been established for a particular test core and material, measurement of the form factor is optional.6.10
39、 For core loss determination, read and record the power from the wattmeter.6.11 For specific exciting power determination, read and record both the rms exciting current and rms secondary voltage asdisplayed on the wattmeter or other rms voltmeters.6.12 For peak permeability determination, read and r
40、ecord the voltage drop across the current-sensing resistor using thepeak-reading voltmeter.6.13 Repeat 6.8 through 6.12 for all test points in order of increasing magnetic flux density. If the required magnetic flux densityis exceeded without acquiring the needed data, the core must be demagnetized
41、before repeating the measurement.7. Calculation (Customary Units)7.1 The cross-sectional area of the test specimen is computed from the mass of core, the density of the material, and themagnetic path length. For a toroidal core the magnetic path length, lm, is equal to the mean circumference or:lm 5
42、 pido1di!2 (1)where:do = outside diameter, cm, anddi = inside diameter, cm.The cross-sectional area, A, in square centimetres is then:A 5 mlm(2)where:m = core mass, g, and = density, g/cm3.7.2 Flux VoltageThe flux voltage corresponding to a given magnetic flux density (assumed to be sinusoidal) is:A
43、927/A927M 183Ef 5=2piBAN2f 31028 (3)where:Ef = flux voltage induced in winding N2, V;B = maximum flux density, G;B = magnetic flux density, G;A = cross-sectional area of core, cm2;N2 = number of secondary turns; andf = frequency, Hz.7.3 Specific Core LossThe core loss per pound is:PcB;f!5453.6 SN1N2
44、DW 2K!m (4)where:Pc(B;f) = specific core loss at magnetic flux density B and frequency f, W/lb;N1 = number of primary turns;N2 = number of secondary turns;W = power loss indicated by the wattmeter, W;K = correction factor for losses due to the wattmeter, W; andm = mass of test core, g.The correction
45、 factor in electronic wattmeters tends to be very small and is usually negligible. Refer to the wattmeter operatingmanual for specific instructions on computing this correction factor.7.4 Specific Exciting PowerThe specific exciting power is calculated from the rms value of exciting current and rms
46、secondaryvoltage with all other secondary burden either subtracted or removed. The latter condition usually applies when high-inputimpedance-measurement equipment is used. The equation is:PzB;f!5453.6 SN1N2DVIm (5)where:Pz(B;f) = specific exciting power at magnetic flux density B and frequency f, VA
47、/lb;N1 = number of primary turns;N2 = number of secondary turns;V = rms value of secondary voltage, V;I = rms value of exciting current, A; andm = mass of test core, g.7.5 Peak ac PermeabilityThe peak ac permeability is calculated as:p 5 BmHpm5 BmRlm0.4piN1Ep(6)p 5 BHp05 BRlm0.4piN1Ep(6)where:p = pe
48、ak ac permeability;Bm = peak flux density, G, which is equivalent to the test magnetic flux density for sinusoidal waveforms;B = magnetic flux density, G, which is equivalent to the test magnetic flux density for sinusoidal waveforms;Hp = peak magnetic field strength, Oe;m = magnetic constant equal
49、to 1, unitless in cgs-emu;0 = magnetic constant equal to 1, unitless in cgs-emu;N1 = number of primary turns;Ep = peak voltage read across the current-sensing resistor, V;R = resistance of the current-sensing resistor, ; andlm = magnetic path length, cm.8. Calculation (SI Units)8.1 The cross-sectional area of the test specimen is computed from the mass of core, the density of the material, and themagnetic path length. For a toroidal core the magnetic path length, lm, is equal to the mean circumference or:A927/A927M 184lm 5 pido1di!2 (7)where:do
