ASTM A712-1997(2002) Standard Test Method for Electrical Resistivity of Soft Magnetic Alloys《软磁性合金电阻率的标准试验方法》.pdf
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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
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