1、Designation: A912/A912M 11Standard Test Method forAlternating-Current Magnetic Properties of AmorphousMaterials at Power Frequencies Using Wattmeter-Ammeter-Voltmeter Method with Toroidal Specimens1This standard is issued under the fixed designation A912/A912M; the number immediately following the d
2、esignation indicates the 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 tes
3、ts for various magneticproperties of amorphous materials at power frequencies 25 to400 Hz using a toroidal test transformer. The term “toroidaltest transformer” is used to describe the test device, reservingthe term “specimen” to refer to the material used in the test.The test specimen consists of t
4、oroidally wound flat strip.1.2 This test method covers the determination of core loss,exciting power, rms and peak exciting current, several types ofac permeability, and related properties under ac magnetizationat moderate and high inductions at power frequencies 25 to 70Hz.1.3 With proper instrumen
5、tation and specimen preparation,this test method is acceptable for measurements at frequenciesfrom 5 Hz to 100 kHz. Proper instrumentation implies that alltest instruments have the required frequency bandwidth. Alsosee Annex A2.1.4 This test method also provides procedures for calculat-ing impedance
6、 permeability from measured values of rmsexciting current and for calculating ac peak permeability frommeasured peak values of total exciting current at magnetic fieldstrengths up to about 10 Oe 796 A/m.1.5 Explanations of symbols and brief definitions appear inthe text of this test method. The offi
7、cial symbols and definitionsare listed in Terminology A340.1.6 This test method shall be used in conjunction withPractice A34/A34M.1.7 The values and equations stated in customary (cgs-emuand inch-pound) units or SI units are to be regarded separatelyas standard. Within this standard, SI units are s
8、hown inbrackets. The values stated in each system may not be exactequivalents; therefore, each system shall be used independentlyof the other. Combining values from the two systems mayresult in nonconformance with this standard.1.8 This standard does not purport to address all of thesafety concerns,
9、 if any, associated with its use. It is theresponsibility of the user of this standard 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:2A34/A34M Practice for Sampling and Procureme
10、nt Testingof Magnetic MaterialsA340 Terminology of Symbols and Definitions Relating toMagnetic TestingA343/A343M Test Method for Alternating-Current Mag-netic Properties of Materials at Power Frequencies UsingWattmeter-Ammeter-Voltmeter Method and 25-cm EpsteinTest FrameA901 Specification for Amorph
11、ous Magnetic Core Alloys,Semi-Processed TypesC693 Test Method for Density of Glass by Buoyancy3. Significance and Use3.1 This test method provides a satisfactory means ofdetermining various ac magnetic properties of amorphousmagnetic materials.3.2 The procedures described herein are suitable for use
12、 byproducers and users of magnetic materials for materials speci-fication acceptance and manufacturing control.3.3 The procedures described herein may be adapted for usewith specimens of other alloys and other toroidal forms.4. Interferences4.1 Test methods using toroidal test transformers are espe-
13、cially useful for evaluating the magnetic properties of amaterial. There are, however, several important requirementsto be met when determining the material characteristics.1This test method is under the jurisdiction of ASTM Committee A06 onMagnetic Properties and is the direct responsibility of Sub
14、committeeA06.01 on TestMethods.Current edition approved Oct. 1, 2011. Published November 2011. Originallyapproved in 1992. Last previous edition approved in 2004 as A912/A912M04.DOI: 10.1520/A0912_A0912M-11.2For referenced ASTM standards, visit the ASTM website, www.astm.org, orcontact ASTM Customer
15、 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 Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.4.1.1 The ratio of inside to outside di
16、ameter must be 0.82 orgreater, or the magnetic field strength will be excessivelynonuniform throughout the test specimen and the measuredparameters will not represent the basic material properties.4.1.2 To best represent the average material properties, thecross-sectional area of the toroid should b
17、e uniform and thewinding should be designed to avoid nonuniform induction.4.1.3 Preparation of test specimens, especially of stresssensitive alloys, is critical. Stresses that are introduced into flatstrip material when it is wound into a toroid depend on thediameter of the resulting toroid, the thi
18、ckness and uniformity ofthe material, and the winding tension. These stresses shall beremoved or reduced by annealing. The annealing conditions(time, temperature, and atmosphere) are a function of thematerial chosen. The details of sample preparation must beagreed upon between the producer and user.
19、 Suggested condi-tions for preparation of amorphous specimens are contained inAnnex A2, Annex A3, Annex A4, and Annex A5.5. Apparatus5.1 The apparatus shall consist of as many of the componentparts shown in the basic block circuit diagram (Fig. 1)asarerequired to perform the desired measurement func
20、tions.5.2 Toroidal Test TransformerThe test transformer shallconsist of a toroidal specimen, prepared as directed in AnnexA2, enclosed by primary and secondary windings. When thetest specimen is small or especially stressed, the use of aprotective case, bobbin, spool, or core form is necessary, seeA
21、nnex A3.5.2.1 The primary and secondary windings may be anynumber of turns suited to the instrumentation, mass of speci-men, and test frequency. A 1:1 turns ratio is recommended. Anair-flux compensator is to be used whenever the air flux is ameasurable fraction of the total flux.5.3 Instruments:5.3.
22、1 Electronic digital instruments are preferred for use inthis test method. The use of analog instruments is permittedprovided the requirements given in 5.3.2-5.5.2 as well as therequirements given in Test Method A343/A343M are met.5.3.1.1 The electrical impedance and accuracy requirementsare given i
23、n 5.3.2-5.5.2. The operating principles for thevarious instruments are not specified.5.3.1.2 Combination instruments (volt-watt-ammeters) maybe used provided the requirements given in 5.3.2-5.5.2 for theindividual instruments are met.5.3.1.3 Automatic or data logging equipment may be used.It is pref
24、erable for the operator to have a record available of thespecimen identification and measured values of the tests beingperformed.5.3.1.4 Although electronic digital equipment usually failscatastrophically and errors are easily detected, it is incumbentupon the user of this test method to ensure that
25、 the instrumentscontinue to meet the performance requirements.5.3.2 Flux VoltmeterA full-wave, true-average voltmeter,with scale reading in average volts times=2 p/4 so that itsindications will be identical with those of a true rms voltmeteron a pure sinusoidal voltage, shall be provided for evaluat
26、ingthe peak value of the test induction. To produce the estimatedprecision of test under this test method, the full-scale metererrors shall not exceed 60.25 % (Note 1). Meters of 60.5 % ormore error may be used at reduced accuracy.5.3.3 RMS VoltmeterAtrue rms-indicating voltmeter shallbe provided fo
27、r evaluating the form factor of the voltageinduced in the secondary winding of the test fixture and forevaluating the instrument losses. The accuracy of the rmsvoltmeter shall be the same as specified for the flux voltmeter.5.3.3.1 The normally high input impedance of digital fluxand rms voltmeters
28、will minimize loading effects and reducethe magnitude of instrument losses to an insignificant value.5.3.3.2 An electronic scaling amplifier may be used to causethe flux voltmeter and the rms voltmeter to indicate directly inunits of induction. The input impedance of the scaling ampli-fier must be h
29、igh enough to minimize loading effects andinstrument losses. The combination of a basic instrument and ascaling device must conform to the specifications stated above.NOTE 1Inaccuracies in setting the flux voltage produce errors ap-proximately two times as large in the specific core loss.5.4 Wattmet
30、erThe full-scale accuracy of the wattmetermust not be poorer than 0.25 % at the frequency of test and atunity power factor. The power factor encountered by a watt-meter during a core-loss test on a specimen is always less thanunity and, at inductions far above the knee of the magnetizationcurve, app
31、roaches zero. The wattmeter must maintain adequateaccuracy (1 % of reading) even at the most severe (lowest)power factor that is presented to it. Variable scaling devicesmay be used to cause the wattmeter to indicate directly in unitsof specific core loss if the combination of basic instrument andsc
32、aling devices conforms to the specifications stated here.5.4.1 Electronic Digital WattmeterAn electronic digitalwattmeter is preferred in this test method because of its highsensitivity, digital readout, and its capability for direct inter-facing with electronic data acquisition systems.5.4.1.1 The
33、voltage input circuitry of the electronic digitalwattmeter must have an input impedance high enough thatconnection of the circuitry, during testing, to the secondarywinding of the test fixture does not change the terminal voltageof the secondary by more than 0.05 %. Also, the voltage inputcircuitry
34、must be capable of accepting the maximum peakvoltage, which is induced in the secondary winding duringtesting.FIG. 1 Basic Circuit Diagram for Wattmeter MethodA912/A912M 1125.4.1.2 The current input circuitry of the electronic digitalwattmeter should have as low an input impedance as possible,prefer
35、ably no more than 0.1 V, otherwise the flux waveformdistortion can be corrected for as described in 9.3. The currentinput circuitry must be capable of accepting the maximum rmscurrent and the maximum peak current drawn by the primarywinding of the test transformer when core-loss tests are beingperfo
36、rmed. In particular, since the primary current will be verynonsinusoidal (peaked) if core-loss tests are performed on aspecimen at inductions above the knee of the magnetizingcurve, the crest factor capability of the current input circuitryshould be 4 or more.5.4.2 Waveform CalculatorA waveform calc
37、ulator, incombination with a digitizing oscilloscope, may be used inplace of the wattmeter for core-loss measurements, providedthat it meets the accuracy requirements given in 5.4. Thisequipment is able to measure, compute, and display the rms,average, and peak values for current and flux voltage, a
38、s wellas measure the core loss and excitation power demand. It isconvenient for making a large number of repetitive measure-ments. See Appendix X2 for details regarding these instru-ments.5.4.2.1 The current and flux sensing leads must be con-nected in the proper phase relationship.5.4.2.2 The norma
39、lly high input impedance of these instru-ments (approximately 1 MV) reduces possible errors as a resultof instrument loading to negligible levels.5.5 AmmetersTwo types of current measurements areused in conjunction with this test method: rms current valuesare used for calculating exciting power and
40、impedance perme-ability while peak current values are used for calculating peakpermeability. The preferred method for measuring excitingcurrent is to measure the voltage drop across a low value,noninductive resistor in series with the primary windings.5.5.1 rms AmmeterA true rms voltmeter in paralle
41、l withthe series resistor is required if measurements of rms excitingcurrent are to be made; rms exciting power, rms specificexciting power, and impedance permeability are calculatedfrom rms exciting current values. A nominal 1 % accuracy isrequired for this instrument.5.5.2 Peak AmmeterThe peak amm
42、eter consists of avoltmeter whose indications are proportional to the peak-to-peak value of the voltage drop that results when the excitingcurrent flows through a low value of standard resistanceconnected in series with the primary winding of the testtransformer. This peak-to-peak reading voltmeter
43、should havea nominal full-scale accuracy of at least 3 % at the testfrequency and be able to accommodate a voltage with a crestfactor of 5 or more.5.6 Series ResistorThe standard series resistor (usually inthe range 0.1 to 1.0 V) that carries the exciting current musthave adequate current-carrying c
44、apacity and be accurate to atleast 60.1 %. It must have negligible temperature and fre-quency variation with the conditions applicable to this testmethod. If desired, the value of the resistor may be such thatthe peak-reading voltmeter indicates directly in terms of peakmagnetic field strength provi
45、ded that the resistor conforms tothe limitations stated herein.5.7 Power SupplyAsource of sinusoidal test power of lowinternal impedance and excellent voltage and frequency stabil-ity is required for this test. The voltage for the test circuit maybe adjustable by use of a tapped transformer between
46、thesource and the test circuit or by generator field control. Theharmonic content of the voltage output from the source underthe heaviest test load should not exceed 1 %. For testing atcommercial power frequencies, the volt-ampere rating of thesource and its associated voltage control equipment shou
47、ld beadequate to supply the requirements of the test specimenwithout an excessive increase in the distortion of the voltagewaveform. Voltage stability within 60.1 % is necessary forprecise work. For testing at commercial frequencies, low-distortion line voltage regulating equipment is available. The
48、frequency of the source should be accurately controlled within60.1 % of the nominal value.5.7.1 An electronic power source consisting of a low-distortion oscillator (Note 2) and a linear amplifier makes anacceptable source of test power. The form factor of the testvoltage should be as close to=2 p/4
49、 as practicable andmust be within 61 % of this value. The line power for theelectronic oscillator and amplifier should come from a voltage-regulated source to ensure voltage stability within 0.1 %, andthe output of the system should be monitored with an accuratefrequency-indicating device to see that control of the frequencyis maintained to within 60.1 % or better. It is permissible touse an amplifier with negative feedback to reduce the wave-form distortion.NOTE 2It is advisable when testing at power line frequency to havethe oscillator synchronized with the power
