1、Designation: A 712 97 (Reapproved 2002)Standard Test Method forElectrical Resistivity of Soft Magnetic Alloys1This standard is issued under the fixed designation A 712; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revision, the year of la
2、st revision. A number in parentheses indicates the year of last reapproval. Asuperscript epsilon (e) indicates an editorial change since the last revision or reapproval.1. Scope1.1 This test method covers the measurement of electricalresistivity of strip or bar specimens of soft magnetic alloys.1.2
3、The values are stated only in SI units and are to beregarded as standard.1.3 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 standard to establish appro-priate safety and health practices and determine
4、the applica-bility of regulatory limitations prior to use.2. Referenced Documents2.1 ASTM Standards:A 34/A 34M Practice for Sampling and Procurement Test-ing of Magnetic Materials23. Summary of Test Method3.1 The electrical resistance of a 0.25-m long (minimum)test specimen is measured with a Kelvin
5、-type resistance bridgeor a digital multimeter or the potentiometer-ammeter method.The resistivity is then calculated from the resistance measure-ment and the dimensions of the specimen and is known as theelectrical resistivity of the material. This value is equal to theresistance between opposite f
6、aces of a cube of unit dimensions.4. Apparatus4.1 Kelvin-type resistance bridge or a digital multimeter ora dc potentiometer and dc ammeter providing resistancemeasurements to an accuracy within 0.5 % of the accepted truevalue.5. Sampling5.1 Samples shall be representative of the material in thephys
7、ical condition as shipped or agreed upon by the manufac-turer and the purchaser.6. Test Specimen6.1 The test specimen shall be a straight strip or bar or wireof substantially uniform cross-sectional area.6.2 It shall have a minimum length of 0.25 m. Stripspecimens preferably should have a uniform wi
8、dth of 0.03 mminimum, unless not available.6.2.1 If width of the strip material to be sampled preventsobtaining a sample of 0.03-m minimum width, the specimenwidth to be used shall be the maximum obtainable and shall beagreed upon between the manufacturer and the purchaser.6.2.2 Bars and wires havin
9、g circular, rectangular, or othersections shall be used in the sectional dimensions as produced,unless they are so large as to require cutting a representativesample of suitable dimensions.6.3 It shall be free of obvious surface defects.6.4 The surface shall be cleaned by wiping with a cloth. Oiland
10、 grease, if present on the surface, shall be removed with asuitable solvent. Normal surface oxide or core plating need notbe removed except in areas in which it is necessary to makesatisfactory electrical contact.7. Procedure7.1 Measure the electrical resistance of the test specimenusing a Kelvin-ty
11、pe resistance bridge or a digital multimeter orpotentiometer-ammeter system having separate current andpotential leads.7.2 The distance between each potential lead contact and thecorresponding current lead contact shall be at least twice thewidth of the test specimen with the two potential contacts
12、lyingbetween the current contacts. The distance between the poten-tial contacts shall be not less than 0.12 m.7.3 The dimension of each potential contact in the directionof the length of the specimen shall be not more than 0.5 % ofthe distance between potential contacts.7.4 The contacts to the speci
13、men shall be located centrallywith respect to the specimens width dimension, and thecurrent contacts shall cover more than 80 % of the width. Areliable contact shall be made with the specimen by both thecurrent and potential leads.7.5 Specimen temperature during test should be about 25C.1This test m
14、ethod is under the jurisdiction of ASTM Committee A06 onMagnetic Properties and is the direct responsibility of Subcommittee A06.01on TestMethods.Current edition approved Oct. 10, 1997. Published December 1998. Originallypublished as A 712 - 75. Last previous edition A 712 - 75.2Annual Book of ASTM
15、Standards, Vol 03.04.1Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.7.6 To eliminate errors as a result of contact potential, taketwo readings, one direct and one with the current reversed, inclose succession.7.7 The electrical curr
16、ent in the test specimen must belimited to avoid overheating but must be adequate to providesufficient sensitivity to show an out-of-balance condition whenthe resistance reading is changed 0.5 % of the value recorded.If the current is too low, sensitivity is low also, and a balancecan be shown for a
17、 broad range of resistance.8. Calculation8.1 Strip Specimens:8.1.1 Determine the average cross-sectional area of the testspecimen from the weight, length, and density as follows:A 5 m/ld (1)where:A = cross-sectional area of test specimen, m2;m = mass of test specimen, kg;l = length of test specimen,
18、 m; andd = density of test specimen, kg/m3, determined in accor-dance with Practice A 34/A 34M.8.1.2 Eq 1 assumes a negligible mass of any coatingmaterial.8.2 Bar and Wire SpecimensThe cross-sectional area ofthe test specimen shall be based on direct measurements witha micrometer or caliper.8.3 Calc
19、ulate resistivity from the measured value of electri-cal resistance and the cross-sectional area as follows:r5RA/l2(2)where:r = electrical resistivity of the material, V m;R = resistance of electrical path, V;A = cross-sectional area of electrical path, m2; andl2= length of electrical path between p
20、otential contacts onthe test specimen, m.8.4 The resistivity units in ohm-metres shown in Eq 2 canbe converted to microhm-centimetres by multiplying the ohm-metre figure by 108microhm-centimetres per ohm-metre. Forexample, if the resistivity is 0.25 3 106V m;0.25 3 1063 108V cm/V m is equal to 25 V
21、cm.NOTE 1The resistivities of commercial soft magnetic alloys areshown in Annex A1.9. Precision and Bias9.1 Although no rigorous interlaboratory comparisons ofthis test method have been performed, it is estimated that thereproducibility standard deviation is no greater than 2 % of themean.9.2 The bi
22、as of this test method is believed to be zero.10. Keywords10.1 electrical resistivity; magnetic alloy; potentiometer-ammeter; resistance bridgeANNEX(Mandatory Information)A1. RESISTIVITIESA1.1 This test method assumes the establishment of auniform current density along the test specimen throughout t
23、heregion between the potential contacts. The current contactsshould be in the form of transverse clamps covering at least80 % and preferably the entire width of the specimen. Thepotential contacts can be either knife edge or point contacts.A1.1.1 If a potentiometer is used, a suitable dc source anda
24、mmeter are required to establish and measure the total currentin the specimen, which should be limited to avoid excessiveheating. The required R is then the ratio of the measuredpotential drop to the measured current. When the potentiometeris balanced, no current flows in the potential leads so that
25、 anycontact resistance at the potential points is of no consequence.A1.1.2 The Kelvin bridge is calibrated to read directly theresistance between the potential points without knowledge ofthe current in the specimen. Contact resistance at the potentialpoints and the resistance of the four leads to th
26、e specimen arenot a part of the required R and are usually negligible portionsof the corresponding components of the bridge system.A1.1.3 Digital multimeters used for measuring resistance inthe range required for this test method will be equipped forfour-wire ohm measurements. In the four-wire metho
27、d, acontrolled source current is applied to the resistance to bemeasured via the current leads, and the voltage drop is sensedacross the potential (or sense) leads. Since the input resistanceof the digital multimeter is very large (typically greater than 10MV), the contact resistance between the sen
28、se leads and thespecimen and the resistance of the leads do not affect themeasurement.A1.2 Typical resistivities of iron-silicon-aluminum alloysteel sheets are shown in Fig. A1.1 and other soft magneticalloys in Table A1.1. Commercial electrical steels are low-carbon, silicon-iron, or silicon-alumin
29、um-iron alloys contain-ing up to 3.5 % silicon and only a small amount of aluminum.A 712 97 (2002)2ASTM International takes no position respecting the validity of any patent rights asserted in connection with any item mentionedin this standard. Users of this standard are expressly advised that deter
30、mination of the validity of any such patent rights, and the riskof infringement of such rights, are entirely their own responsibility.This standard is subject to revision at any time by the responsible technical committee and must be reviewed every five years andif not revised, either reapproved or
31、withdrawn. Your comments are invited either for revision of this standard or for additional standardsand should be addressed to ASTM International Headquarters. Your comments will receive careful consideration at a meeting of theresponsible technical committee, which you may attend. If you feel that
32、 your comments have not received a fair hearing you shouldmake your views known to the ASTM Committee on Standards, at the address shown below.This standard is copyrighted by ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959,United States. Individual reprints (
33、single or multiple copies) of this standard may be obtained by contacting ASTM at the aboveaddress or at 610-832-9585 (phone), 610-832-9555 (fax), or serviceastm.org (e-mail); or through the ASTM website(www.astm.org).NOTE 1The linear equation for the graph in this figure is as follows:r = 0.1325 3
34、106+ 0.113 (percent silicon + percent aluminum) 3 106V mwhere r = electrical resistivity in ohm-metres at approximately 25C. The equation is based on the average line drawn through many test points obtainedon commercial grades of electrical steels of various compositions. Individual tests may show d
35、epartures from the average line, which is shown in equationand graphical form for general use and guidance. The intercept constant 0.1325 applies only to steels having alloying elements over about 0.15 %. Asthe percentage of alloying elements decreases to low values, the intercept constant decreases
36、, approaching the value of about 0.107.FIG. A1.1 Electrical Resistivities Versus Composition of Commercial Grades of Electrical SteelsTABLE A1.1 Electrical Resistivity of Soft Magnetic Alloys of Nickel, Chromium, and IronGeneral CompositionTypical ElectricalResistivity, VmGeneral Name36 % Nickel, ba
37、lance iron 0.82 3 106Invar45 % Nickel, balance iron 0.53 45 Permalloy48 % Nickel, balance iron 0.48 High Perm, 49; 475052 % Nickel, balance iron 0.43 52 Alloy65 % Nickel, balance iron 0.22 65 Permalloy77 % Nickel, 5 % copper, 2.6 % chromium,balance iron0.60 Mumetal78.5 % Nickel, balance iron 0.16 78 Permalloy80 % Nickel, 4 % molybdenum, balance iron 0.58 479 Permalloy; Hy Mu 8080 % Nickel, 5 % molybdenum, balance iron 0.60 579 Permalloy; Hy Mu 800 Supermalloy17 % Chromium, balance iron 0.61 Stainless Type 430A 712 97 (2002)3
