1、Designation: A 927/A 927M 04Standard Test Method forAlternating-Current Magnetic Properties of Toroidal CoreSpecimens Using the Voltmeter-Ammeter-WattmeterMethod1This standard is issued under the fixed designation A 927/A 927M; the number immediately following the designation indicates the yearof or
2、iginal 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 (e) indicates an editorial change since the last revision or reapproval.1. Scope1.1 This test method covers the determination of several acmagne
3、tic properties of either laminated ring or toroidal tapewound cores made from flat rolled product.1.2 This test method covers test equipment and proceduresfor determination of specific core loss, specific exciting power,and peak permeability for power and audio frequencies (50 to20 000 Hz) under sin
4、usoidal flux conditions.1.3 This test method, because of the use of a feedback-controlled power amplifier, is well suited for determination ofac magnetic properties at magnetic flux densities above theknee of the magnetization curve and is particularly useful fortesting of high-saturation iron-cobal
5、t alloys (for example,alloys listed in Specification A 801), although use of this testmethod is not restricted to a particular type of material.1.4 This test method shall be used in conjunction withPractice A 34/A 34M and Terminology A 340.1.5 The values and equations stated in customary (cgs-emuand
6、 inch-pound) or SI units are to be regarded separately asstandard. Within this standard, SI units are shown in bracketsexcept for the sections concerning calculations where there areseparate sections for the respective unit systems. The valuesstated in each system may not be exact equivalents; there
7、fore,each system shall be used independently of the other. Combin-ing values from the two systems may result in nonconformancewith this standard.1.6 This standard does not purport to address all of thesafety concerns, if any, associated with its use. It is theresponsibility of the user of this stand
8、ard to establish appro-priate safety and health practices and determine the applica-bility of regulatory limitations prior to use.2. Referenced Documents2.1 ASTM Standards:2A 34/A 34M Practice for Sampling and Procurement Test-ing of Magnetic MaterialsA 340 Terminology of Symbols and Definitions Rel
9、ating toMagnetic TestingA 697/A 697M Test Method for Alternating Current Mag-netic Properties of Laminated Core Specimen Using theVoltmeter-Ammeter-Wattmeter MethodsA 801 Specification for Iron-Cobalt High-Magnetic Satura-tion Alloys (UNS R30005 and K92650)3. Significance and Use3.1 This test method
10、 is a derivative of Test Method A 697/A 697M specifically designed for testing of toroidal coreswhich are not covered in Test Method A 697/A 697M and fortesting at magnetic flux densities above the knee of themagnetization curve.3.2 Specimen size typically ranges from 1 to 1.25 in. 25.4to 31.8 mm in
11、 inside diameter to 1.5 in. 38.1 mm in outsidediameter with weights ranging from 30 to 60 g. Provided thetest equipment is suitably chosen, there is no obvious limit tothe overall size of core that can be tested. If basic materialproperties are desired, then the requirements of 5.1 must beobserved.3
12、.3 The reproducibility and repeatability of this test methodare such that this test method is suitable for design, specifica-tion acceptance, service evaluation, and research and develop-ment.3.4 When testing under sinusoidal flux conditions at mag-netic flux densities approaching saturation, highly
13、 peaked1This test method is under the jurisdiction of ASTM Committee A06 onMagnetic Properties and is the direct responsibility of Subcommittee A06.01 on TestMethods.Current edition approved Oct. 1, 2004. Published October 2004. Originallyapproved in 1994. Last previous edition approved in 1999 as A
14、 927/A 927M 99.2For referenced ASTM standards, visit the ASTM website, www.astm.org, orcontact ASTM Customer Service at serviceastm.org. For Annual Book of ASTMStandards volume information, refer to the standards Document Summary page onthe ASTM website.1Copyright ASTM International, 100 Barr Harbor
15、 Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.magnetizing waveforms will be present, and the test instru-ments used must have crest factor capabilities of at least 3;otherwise erroneous results will be obtained.4. Apparatus4.1 The apparatus for testing under this test method s
16、hallconsist of as many of the components, described below andschematically illustrated in Fig. 1, as required to perform themeasurements.4.2 Signal GeneratorFor testing at other than line fre-quency (50 or 60 Hz), a low distortion sine wave signalgenerator is required. The frequency accuracy of the
17、signalgenerator should be within 60.1 %. To prevent dc biasing ofthe magnetizing current waveform, a blocking capacitor orisolation transformer should be installed between the signalgenerator and power amplifier.4.3 Power AmplifierA linear power amplifier should beused.3The signal from the secondary
18、 winding of the testspecimen is used for negative feedback control of the magne-tizing waveform. Depending on the power amplifier used, itmay be necessary to install feedback signal conditioningequipment such as an attenuator or amplifier; however, thesignal conditioning equipment must not distort t
19、he feedbackwaveform nor load the secondary winding. Fig. 1 also showsan audio choke connecting the output and feedback terminalsof the amplifier. This choke is intended to prevent dc bias beingintroduced into the magnetizing waveform by providing dcfeedback to the power amplifier. Without such a cho
20、ke, the dcoffset current present in certain power amplifiers will result inlarge dc output currents. This choke may not be neededdepending on the make and model of power supply. Furtherreduction or elimination of bias can be achieved by installingan isolation transformer to transformer couple the pr
21、imarycircuit.4.4 WattmeterAn electronic wattmeter with appropriatevoltage, current and wattage ranges, and bandwidth must beused. The full-scale accuracy of the wattmeter must be betterthan 60.5 %. The wattmeter must have a crest factor capabilityof at least 3 and be capable of accurate measurements
22、 atlow-power factors. The wattmeter must be able to measure rmscurrent and rms voltage to an accuracy of 60.5 % or better;otherwise, separate instruments meeting this accuracy require-ment must be used.4.5 Flux VoltmeterThe flux voltmeter must be a trueaverage responding, high-impedance voltmeter ca
23、librated toread=2 p/4 times the full wave rectified average voltage sothat its indications will be identical to those of a true rmsvoltmeter when reading a pure sinusoidal voltage. The ratedfull-scale accuracy must be 60.5 % or better.4.6 Current-Sensing Resistor (Optional)When peak per-meability is
24、 to be measured, a noninductive, high-precision,low-thermal coefficient of resistance current-sensing resistorshall be used. The resistor must be rated to carry the maximumcurrent used in the test.4.7 Peak Voltmeter (Optional)When peak permeability isto be determined, a high-impedance peak-reading v
25、oltmetershall be used to measure the voltage drop across the current-sensing resistor. The voltmeter must have a full-scale accuracyof 61 % or better, a crest factor of at least 3, and appropriatebandwidth.4.8 Oscilloscope (Optional)An oscilloscope displayingboth the magnetizing current waveform and
26、 secondary voltagepermits the operator to observe the waveforms. This is particu-larly useful when setting up the test for the first time. Theoscilloscope must have a very high input impedance to avoidloading of the secondary winding.5. Test Specimen5.1 The test specimen must be either a stack of to
27、roidal(washer ring) laminations formed by punching, machining, oretching or a toroidal tape wound core. For measurement ofbasic material properties, the ratio of inside to outside diametermust be 0.82 or greater.6. Procedure6.1 The test specimen should be heat treated after fabrica-tion. Bent or oth
28、erwise damaged laminations or tape cores shallbe discarded.6.2 The core shall be weighed to an accuracy of 60.1 % orbetter and the inside and outside diameters measured to anaccuracy of 0.1 % or better.6.3 The laminations or tape core should be enclosed in arigid, nonconductive case (core box) or pl
29、aced in a suitablefixture to avoid winding stresses. The test core should fill thecore box or fixture as fully as possible to minimize air flux.6.4 Primary and secondary windings, N1and N2, are ap-plied; the secondary winding should be applied first. Bothwindings should be uniformly wound over the c
30、ircumferenceof the toroid. The secondary winding may use finer diameterwire than the primary winding, which should be of sufficientdiameter to carry the magnetizing current without overheating.Alternately, a fabricated magnetizing fixture may be usedprovided the windings are uniformly distributed ov
31、er the lengthof the core.3Audio amplifiers are suitable in some instances, although the small specimencross section and the relatively few primary turns typically used results in a low Qcircuit and, therefore, difficulty in maintaining sinusoidal flux at magnetic fluxdensities approaching saturation
32、. In addition, an impedance matching transformermay be required to improve power transfer.FIG. 1 Schematic Illustration of Test ApparatusA 927/A 927M 0426.5 The flux voltage, Ef, induced in the secondary winding,N2, at the required magnetic flux density, Bm, shall be com-puted using the equation fou
33、nd in 7.2 or 8.2.6.6 The test specimen is connected to the test apparatus anddemagnetized. Demagnetization must be done by smoothlyreducing the magnetizing current starting from a magnetic fluxdensity above the knee of the magnetization curve and at thetest frequency.6.7 The magnetizing current is i
34、ncreased to obtain the fluxvoltage corresponding to the lowest required magnetic fluxdensity.6.8 The form factor of the secondary voltage is computed bydividing the rms secondary voltage by the flux voltage. Theform factor must be within 61 % of the value for a sine wavefor testing conducted in acco
35、rdance with this test method. Oncetest conditions have been established for a particular test coreand material, measurement of the form factor is optional.6.9 For core loss determination, read and record the powerfrom the wattmeter.6.10 For specific exciting power determination, read andrecord both
36、the rms exciting current and rms secondary voltageas displayed on the wattmeter or other rms voltmeters.6.11 For peak permeability determination, read and recordthe voltage drop across the current-sensing resistor using thepeak-reading voltmeter.6.12 Repeat 6.7 through 6.11 for all test points in or
37、der ofincreasing magnetic flux density. If the required magnetic fluxdensity is exceeded without acquiring the needed data, the coremust be demagnetized before repeating the measurement.7. Calculation (Customary Units)7.1 The cross-sectional area of the test specimen is com-puted from the mass of co
38、re, the density of the material, and themagnetic path length. For a toroidal core the magnetic pathlength, lm, is equal to the mean circumference or:lm5pdo1 di!2(1)where:do= outside diameter, cm anddi= inside diameter, cm.The cross-sectional area, A, in square centimetres is then:A 5mdlm(2)where:m =
39、 core mass, g andd = density, g/cm3.7.2 Flux VoltageThe flux voltage corresponding to agiven flux density (assumed to be sinusoidal) is:Ef5 =2pBAN2f 3 1028(3)where:Ef= flux voltage induced in winding N2,V;B = maximum flux density, G;A = cross-sectional area of core, cm2;N2= number of secondary turns
40、; andf = frequency, Hz.7.3 Specific Core LossThe core loss per pound is:PcB;f!5453.6SN1N2DW 2 K!m(4)where:Pc(B;f)= specific core loss at magnetic flux density B andfrequency f, W/lb;N1= number of primary turns;N2= number of secondary turns;W = power loss indicated by the wattmeter, W;K = correction
41、factor for losses due to the wattmeter,W; andm = mass of test core, g.The correction factor in electronic wattmeters tends to bevery small and is usually negligible. Refer to the wattmeteroperating manual for specific instructions on computing thiscorrection factor.7.4 Specific Exciting PowerThe spe
42、cific exciting power iscalculated from the rms value of exciting current and rmssecondary voltage with all other secondary burden eithersubtracted or removed. The latter condition usually applieswhen high-input impedance-measurement equipment is used.The equation is:PzB;f!5453.6SN1N2DVIm(5)where:Pz(
43、B;f)= specific exciting power at magnetic flux densityand frequency f, VA/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 iscalculated
44、 as:p5BmHpGm5BmRlm0.4pN1Ep(6)where:p= peak ac permeability;Bm= peak flux density, G, which is equivalent to the testmagnetic flux density for sinusoidal waveforms;Hp= peak magnetic field strength, Oe;Gm= magnetic constant equal to 1, unitless in cgs-emu;N1= number of primary turns;Ep= peak voltage r
45、ead across the current-sensing resistor,V;R = resistance of the current-sensing resistor, V; andlm= magnetic path length, cm.8. Calculation (SI Units)8.1 The cross-sectional area of the test specimen is com-puted from the mass of core, the density of the material, and themagnetic path length. For a
46、toroidal core the magnetic pathlength, lm, is equal to the mean circumference or:lm5pdo1 di!2(7)A 927/A 927M 043where:do= outside diameter, m anddi= inside diameter, m.The cross-sectional area, A, in square metres, is then:A 5mdlm(8)where:m = core mass, kgd = density, kg/m3.8.2 Flux VoltageThe flux
47、voltage corresponding to agiven flux density (assumed to be sinusoidal) is:Ef5 =2pBAN2f (9)where:Ef= flux voltage induced in winding N2,V;B = maximum flux density, T;A = cross-sectional area of core, m2;N2= number of secondary turns; andf = frequency, Hz.8.3 Specific Core LossThe core loss per kilog
48、ram is:PcB;f!5SN1N2DW 2 K!m(10)where:Pc(B;f)= specific core loss at magnetic flux density B andfrequency f, W/kg;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; and,m = mass of test core,
49、kg.The correction factor in electronic wattmeters tends to bevery small and is usually negligible. Refer to the wattmeteroperating manual for specific instructions on computing thiscorrection factor.8.4 Specific Exciting PowerThe specific exciting power iscalculated from the rms value of exciting current and rmssecondary voltage with all other secondary burden eithersubtracted or removed. The latter condition usually applieswhen high-input impedance-measurement equipment is used.The equation is:PzB;f!5SN1N2DVIm(11)where:Pz(B;f)= specific exciting power a
