# ASTM A340-17a

Designation: A340 − 17aStandard Terminology ofSymbols and Definitions Relating to Magnetic Testing1This standard is issued under the fixed designation A340; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. Asuperscript epsilon (´) indicates an editorial change since the last revision or reapproval.INTRODUCTIONIn preparing this glossary of terms, an attempt has been made to avoid, where possible, vectoranalysis and differential equations so as to make the definitions more intelligible to the average workerin the field of magnetic testing. In some cases, rigorous treatment has been sacrificed to securesimplicity, but it is believed that none of the definitions will prove to be misleading.It is the intent of this glossary to be consistent in the use of symbols and units with those found inANSI/IEEE 260-1978 and USA Standard Y 10.5-1968.Part 1—Symbols Used in Magnetic TestingSymbol Termα cross-sectional area of B coilA cross-sectional area of specimenA solid areaBHmagnetic flux densitymagnetic induction∆B excursion range of inductionBb· biased inductionBdremanent inductionBdmremanenceBdHdenergy product(BH)maxmaximum energy productB∆incremental inductionBiintrinsic inductionBmmaximum induction in a hysteresis loopBmaxmaximum induction in a flux current loopBrresidual inductionBrsretentivityBssaturation inductioncf crest factorCM cyclically magnetized conditiond lamination thicknessDBdemagnetizing coefficientdf distortion factorDmmagnetic dissipation factorE exciting voltageE1induced primary voltageE2induced secondary voltageEfflux voltsf cyclic frequency in hertz^ magnetomotive forceff form factorH magnetic field strength∆H excursion range of magnetic field strengthHbbiasing magnetic field strengthHcBcoercive field strengthHcJintrinsic coercive field strengthHddemagnetizing field strengthH∆incremental magnetic field strengthHgair gap magnetic field strengthHLac magnetic field strength (from an assumedpeak value of magnetizing current)Hmmaximum magnetic field strength in a hyster-esis loopHmaxmaximum magnetic field strength in a flux-current loopHpac magnetic field strength (from a measuredpeak value of exciting current)Htinstantaneous magnetic field strength (coinci-dent with Bmax)Hzac magnetic field strength force (from an as-sumed peak value of exciting current)I ac exciting current (rms value)Icac core loss current (rms value)Idcconstant currentImac magnetizing current (rms value)J magnetic polarizationk coupling coefficient! flux path length!1effective flux path length!ggap length+ (also φ N ) flux linkage+mmutual flux linkage1This terminology is under the jurisdiction of ASTM Committee A06 onMagnetic Properties and is the direct responsibility of Subcommittee A06.92 onTerminology and Definitions.Current edition approved Oct. 15, 2017. Published October 2017. Originallyapproved in 1949. Last previous edition approved in 2017 as A340 – 17. DOI:10.1520/A0340-17A.Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United StatesThis international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for theDevelopment of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.1L self inductanceL1core inductanceL∆incremental inductanceLiintrinsic inductanceLmmutual inductanceL0initial inductanceLsseries inductanceLwwinding inductancem magnetic momentM magnetizationm total mass of a specimenm1active mass of a specimenNDdemagnetizing factorN1turns in a primary windingN2turns in a secondary windingN1I/!1ac excitationp magnetic pole strength3 permeanceP active (real) powerPaapparent powerPa (B;f)specific apparent powerPctotal core lossPc (B;f)specific core lossPc∆incremental core lossPenormal eddy current core lossP∆eincremental eddy current core lossPhnormal hysteresis core lossP∆hincremental hysteresis core lossPqreactive (quadrature) powerPrresidual core lossPwwinding loss (copper loss)Pzexciting powerPz (B;f)specific exciting powerQmmagnetic storage factor5 reluctanceR1core resistanceRwwinding resistanceS lamination factor (stacking factor)SCM symmetrically cyclically magnetized conditionTcCurie temperaturew lamination widthWhhysteresis loop lossα¯linear expansion, coefficient (average)∆χ incremental toleranceβ hysteretic angleγ loss anglecos γ magnetic power factorγpproton gyromagnetic ratioµ0magnetic constantδ densityκ susceptibilityac Permeabilities:µaideal permeabilityµLinductance permeabilityµ∆L incremental inductance permeabilityµ0dinitial dynamic permeabilityµppeak permeabilityµ∆pincremental peak permeabilityµiinstantaneous permeabilityµzimpedance permeabilityµ∆zincremental impedance permeabilitydc Permeabilities:µ normal permeabilityµabsabsolute permeabilityµddifferential permeabilityµ∆incremental permeabilityµeffeffective circuit permeabilityµ∆iincremental intrinsic permeabilityµmmaximum permeabilityµiinitial permeabilityµrrelative permeabilityµrevreversible permeabilityµ /cot γ figure of meritν reluctivityπ the numeric 3.1416ρ resistivityφ magnetic fluxφN flux linkage (see +)χ mass susceptibilityχ0initial susceptibilityω angular frequency in radians per secondPart 2—Definition of Terms Used in Magnetic Testingac excitation, N1I/ℓ1—the ratio of the rms ampere-turns ofexciting current in the primary winding of an inductor to theeffective flux path length of the inductor.active (real) power, P—the product of the rms current, I,inanelectrical circuit, the rms voltage, E, across the circuit, andthe cosine of the angular phase difference, θ between thecurrent and the voltage.P 5 EI cosθDISCUSSION—The portion of the active power that is expended in amagnetic core is the total core loss, Pc.aging coefficient—the percentage change in a specific mag-netic property resulting from a specific aging treatment.DISCUSSION—The aging treatments usually specified are:(a) 100 h at 150°C or(b) 600 h at 100°C.aging, magnetic—the change in the magnetic properties of amaterial resulting from metallurgic change due to a normalor specified aging condition.DISCUSSION—This term implies a deterioration of the magneticproperties of magnetic materials for electronic and electricalapplications, unless otherwise specified.air-gap magnetic field strength, Hg—the magnetic fieldstrength required to produce the induction existing at somepoint in a nonmagnetic gap in a magnetic circuit.DISCUSSION—In the cgs-emu system of units, Hgis numerically equalto the induction existing at such a point and exceeds the magnetic fieldstrength in the magnetic material.amorphous alloy—a semiprocessed alloy produced by a rapidquenching, direct casting process resulting in metals withnoncrystalline structure.ampere (turn), A—the unit of magnetomotive force in the SIsystem of units. The symbol A represents the unit of electriccurrent, ampere, in the SI system of units.ampere per metre, A/m—the unit of magnetic field strength inthe SI system of units.anisotropic material—a material in which the magnetic prop-erties differ in various directions.anisotropy of loss—the ratio of the specific core loss measuredwith flux parallel to the rolling direction to the specific coreloss with flux perpendicular to the rolling direction.anisotropy of loss 5Pc ~B;f! lPc ~B;f! tA340 − 17a2where:Pc (B;f) l= specific core loss value with flux parallel to therolling direction, W/lb [W/kg], andPc (B;f) t= specific core loss value with flux perpendicular tothe rolling direction, W/lb [W/kg].DISCUSSION—This definition of anisotropy normally applies to elec-trical steels with measurements made in an Epstein frame at a fluxdensity of 15 kG [1.5 T] and a frequency of 60 Hz (see Test MethodA343).anisotropy of permeability—the ratio of relative peak perme-ability measured with flux parallel to the rolling direction tothe relative peak permeability measured with flux perpen-dicular to the rolling direction.anisotropy of permeability 5µprlµprtwhere:µprl= relative peak permeability value with flux parallel tothe rolling direction, andµprt= relative peak permeability value with flux perpendicu-lar to the rolling direction.DISCUSSION—This definition of anisotropy normally applies to elec-trical steels with measurements made in an Epstein frame at a fluxdensity of 15 kG [1.5 T] and a frequency of 60 Hz (see Test MethodA343).antiferromagnetic material—a feebly magnetic material inwhich almost equal magnetic moments are lined up antipar-allel to each other. Its susceptibility increases as the tem-perature is raised until a critical (Neél) temperature isreached; above this temperature the material becomes para-magnetic.apparent power, Pa—the product (volt-amperes) of the rmsexciting current and the applied rms terminal voltage in anelectric circuit containing inductive impedance. The compo-nents of this impedance as a result of the winding will belinear, while the components as a result of the magnetic corewill be nonlinear. The unit of apparent power is the volt-ampere, VA.apparent power, specific, Pa(B;f)—the value of the apparentpower divided by the active mass of the specimen, that is,volt-amperes per unit mass. The values of voltage andcurrent are those developed at a maximum value of cycli-cally varying induction B and specified frequency f.area, A—the geometric cross-sectional area of a magnetic pathwhich is perpendicular to the direction of the induction.Bloch wall—a domain wall in which the magnetic moment atany point is substantially parallel to the wall surface. Seealso domain wall.Bohr magneton—a constant that is equal to the magneticmoment of an electron because of its spin. The value of theconstant is (9 274 078 × 10−21erg/gauss or9 274 078 × 10−24J/T).cgs-emu system of units—the system for measuring physicalquantities in which the base units are the centimetre, gram,and second, and the numerical value of the magneticconstant, µ0, is unity.coercive field strength, HcB—the absolute value of the appliedmagnetic field strength (H) required to restore the magneticflux density (B) to zero.DISCUSSION—The symbol Hchas historically been used to denote thecoercive field strength determined from a (B,H) loop. Further use of thissymbol in ASTM A06 standards is deprecated.DISCUSSION—The coercive field strength monotonically increaseswith increasing maximum magnetic field strength (Hm) reaching amaximum or limiting value termed the coercivity. Unless it is knownthat the material has been magnetized to saturation, the term coercivefield strength is preferred.DISCUSSION—The coercive field strength is not completely describedwithout knowing the maximum magnetic flux density (Bm) or maxi-mum magnetic field strength (Hm) used in the measurement.coercive field strength, intrinsic, HcJ—the absolute value ofthe applied magnetic field strength (H) required to restoreeither the magnetic polarization (J) or magnetization (M)tozero.DISCUSSION—The symbol Hcihas historically been used to denote theintrinsic coercive field strength determined from a (Bi,H) loop. Furtheruse of this symbol in ASTM A06 standards is deprecated.DISCUSSION—The intrinsic coercive field strength monotonicallyincreases with increasing maximum magnetic field strength (Hm)reaching a maximum or limiting value termed the intrinsic coercivity.Unless it is known that the material has been magnetized to saturation,the term intrinsic coercive field strength is preferred.DISCUSSION—The measured value of intrinsic coercive field strengthwill be the same whether it is measured from a magnetic polarization(J,H) or a magnetization (M,H) hysteresis loop and will always benumerically larger than the coercive field strength (HcB) measured froma magnetic flux density (B,H) hysteresis loop.DISCUSSION—The intrinsic coercive field strength is not completelydescribed without knowing the maximum magnetic polarization, maxi-mum magnetization or maximum magnetic field strength (Hm) used inthe measurement.coercivity—see coercive field strength.coercivity, intrinsic—see coercive field strength, intrinsic.core, laminated—a magnetic component constructed bystacking suitably thin pieces of magnetic material which arestamped, sheared, or milled from sheet or strip material.Individual pieces usually have an insulating surface coatingto minimize eddy current losses in the assembled core.core, mated—two or more magnetic core segments assembledwith the magnetic flux path perpendicular to the matingsurface.core, powder (dust)—a magnetic core comprised of smallparticles of electrically insulated metallic ferromagneticmaterial. These cores are characterized by low hysteresis andeddy current losses.core, tape-wound—a magnetic component constructed by thespiral winding of strip material onto a suitable mandrel. Thestrip material usually has an insulating surface coating whichreduces interlaminar eddy current losses in the finished core.A340 − 17a3core loss, ac eddy current, incremental, P∆e—the power losscaused by eddy currents in a magnetic material that iscyclically magnetized.core loss, ac eddy current, normal, Pe—the power losses asa result of eddy currents in a magnetic material that issymetrically cyclically magnetized.DISCUSSION—The voltage is generally assumed to be across theparallel combination of core inductance, L1, and core resistance, R1.core loss, ac, incremental, Pc∆—the core loss in a magneticmaterial when the material is subjected simultaneously to adc biasing magnetizing force and an alternating magnetizingforce.core loss, residual, Pr—the portion of the core loss power, Pc,which is not attributed to hysteresis or eddy current lossesfrom classical assumptions.core loss, ac, specific, Pc(B;f)—the active power (watts) ex-pended per unit mass of magnetic material in which there isa cyclically varying induction of a specified maximum value,B, at a specified frequency, f.core loss, ac, (total), Pc—the active power (watts) expended ina magnetic circuit in which there is a cyclically alternatinginduction.DISCUSSION—Measurements of core loss are normally made withsinusoidally alternating induction, or the results are corrected fordeviations from the sinusoidal condition.core loss density—the active power (watts) expended in amagnetic core in which there is a cyclically varying induc-tion of a specified maximum value, B, at a specifiedfrequency, f, divided by the effective volume of the core.DISCUSSION—This parameter is normally used only for non-laminatedcores such as ferrite and powdered cores.core plate—a generic term for any insulating material, formedmetallurigically or applied externally as a thin surfacecoating, on sheet or strip stock used in the construction oflaminated and tape wound cores.coupling coefficient, k —the ratio of the mutual inductancebetween two windings and the geometric mean