1、Designation:A698/A698M15Standard Test Method forMagnetic Shield Efficiency in Attenuating AlternatingMagnetic Fields1This standard is issued under the fixed designation A698/A698M;the number immediately following the designation indicates the yearof original adoption or,in the case of revision,the y
2、ear 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 means for determining theperformance quality of a magnetic shield when placed in amagne
3、tic field of alternating polarity.1.2 This test method provides a means of evaluating andgrading magnetic shielding materials to determine their suit-ability for use in the production of magnetic shields.1.3 This test method shall be used in conjunction with andshall conform to the requirements of P
4、ractice A34/A34M.1.4 The values stated in either SI units or inch-pound unitsare to be regarded separately as standard.The values stated ineach system may not be exact equivalents;therefore,eachsystem shall be used independently of the other.Combiningvalues from the two systems may result in non-con
5、formancewith the standard.1.5 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 the applica-bility of regulatory limitations prior
6、 to use.2.Referenced Documents2.1 ASTM Standards:2A34/A34M Practice for Sampling and Procurement Testingof Magnetic MaterialsA340 Terminology of Symbols and Definitions Relating toMagnetic Testing3.Terminology3.1 The following symbols and abbreviated definitions ap-ply only to this test method(the o
7、fficial symbols and definitionsare listed in Terminology A340):3.2 Definitions of Terms Specific to This Standard:3.2.1 attenuation ratiothe ratio of the measured voltage inthe pickup coil before and after the insertion of the shield undertest,E1/E2.3.3 Abbreviations:3.3.1 Aac ammeter(usually root m
8、ean square(rms)butmay be peak reading type).3.3.2 E1voltage in the pickup coil,after establishing thefield of test but before insertion of the shield into the testposition.3.3.3 E2highest voltage observed in the pickup coil,at thefield of test,while rotating the test shield in the test position.3.3.
9、4 Hpmagnetic field strength,Oe A/m.3.3.5 Ipac magnetizing current,peak amperes.3.3.6 Iac magnetizing current,rms amperes.3.3.7 lclength of demagnetizing air coil,cm m.3.3.8 Nnumber of turns per coil section(one half of totalHelmholtz coil turns).3.3.9 N1number of turns in demagnetizing coil.3.3.10 R
10、mean radius of Helmholtz coil,cm m.3.3.11 Velectronic voltmeter(average volts3/2=2).4.Summary of Test Method4.1 FrequencyTests under this test method are normallyconducted at a test frequency of 60 Hz.NOTE1Other test frequencies are used by mutual agreement.Ingeneral,as test frequencies are increase
11、d,it will be necessary to makecorresponding changes in pickup or test coils and in the size of the powersupply.4.2 Magnetic Field StrengthTests may be conducted atany desired magnetic field strength.The standard test level forac magnetic fields is 0.5 or 2.0 peak Oe 39.8 or 159 peakA/mand in the pre
12、sence of the earths magnetic field(see 9.2).4.3 InstrumentationThe instruments described are for useat 60 Hz.At higher frequencies,electronic voltmeters andpreamplifiers should also be satisfactory.It may be necessaryto change the rms ammeter and power supplies for use athigher test frequencies.It m
13、ay also be desirable to reduce thenumber of area turns in the pickup coil at these frequencies.1This 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 April 1,2015.Publishe
14、d May 2015.Originallyapproved in 1974.Last previous edition approved in 2007 as A698/A698M07.DOI:10.1520/A0698_A0698M-15.2For 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
15、the standards Document Summary page onthe ASTM website.Copyright ASTM International,100 Barr Harbor Drive,PO Box C700,West Conshohocken,PA 19428-2959.United States1 4.4 Field AttenuationThe usable range of attenuationratios is determined by the strength of the starting field and thesensitivity of th
16、e available instrumentation.Measurementsshall not be made when signal voltages cannot be clearlydistinguished from amplifier noise or other transient voltages.5.Significance and Use5.1 This test method provides an easy,accurate,and repro-ducible method for determination of shielding factors(attenu-ation ratios)in simple alternating magnetic fields.5.2 Since the sensing or pickup coil is of finite size,themeasured shielding factor tends to be the average value for thespace enclosed by the coil.Du