1、Designation: E 1629 07Standard Practice forDetermining the Impedance of Absolute Eddy-CurrentProbes1This standard is issued under the fixed designation E 1629; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revision, the year of last revisi
2、on. 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 practice covers a procedure for determining theimpedance of absolute eddy-current probes (bridge-type, air orferrite core,
3、wire wound, shielded, or unshielded) used forfinding material defects in electrically conducting material.This practice is intended to establish a uniform test methodol-ogy to measure the impedance of eddy-current probes prior toreceipt of these probes by the purchaser or the specifier.1.2 Limitatio
4、nsThis practice does not address the charac-terization or measurement of the impedance of differential, a-ccoupled, or transmit/receive types of probes. This practice doesnot address the use of magnetic materials in testing probes.This practice shall not be used as a basis for selection of thebest p
5、robe for a particular application or as a means by whichto calibrate a probe for a specific examination.1.3 The values stated in SI units are to be regarded as thestandard. The values given in parentheses are for informationonly.1.4 This standard does not purport to address all of thesafety concerns
6、, 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 The following document forms a part of this practice tothe
7、extent specified herein:2.2 ASTM Standards:E 1316 Terminology for Nondestructive Examination23. Terminology3.1 DefinitionsThe terminology relating to eddy-currentexamination that appears in Terminology E 1316 shall apply tothe terms used in this practice.3.2 Definitions of Terms Specific to This Sta
8、ndard:3.2.1 eddy-current test block for the purposes of themethod described in this practice, a rectangular block made ofan aluminum alloy (see 6.1.2) to which an active eddy-currentprobe is applied.3.3 Mathematical Symbols:3.3.1 ja symbol used in electrical engineering to represent=21 . It is assoc
9、iated with the restriction to the flow ofelectrical current caused by capacitors and coils.3.3.2 N any number.3.3.3 |N|the magnitude of N, regardless whether N ispositive, negative, or a vector quantity.3.3.4=N the square root of N.3.3.5 (N)2N squared, that is, N 3 N.3.3.6 DN delta N, the change or
10、difference in N.3.4 Abbreviations:Abbreviation:3.4.1 tanused for the tangent function. The tan1, arctangent or inverse tangent function, returns a value that is ameasure of an angle and can be in either degrees or radians.When using a calculator to determine the tan1, care should betaken to determin
11、e whether the answer is in degrees or radianssince the numerical values that represent the same angle aredifferent.3.4.2 cosused for the cosine function.3.4.3 sinused for the sine function.4. Significance and Use4.1 Eddy-current probes may be used for the nondestructiveexamination of parts or struct
12、ures made of electrically conduct-ing materials. Many of these examinations are intended todiscover material defects, such as cracks, that may cause thepart or structure to be unsafe or unfit for service. Eddy-currentprobes that fail to meet the performance level requirements ofthis practice shall n
13、ot be used for the examination of materialor hardware unless the probe is qualified by some other systemor an agreement has been reached by the probe manufacturerand the purchaser, or both.5. General Practice5.1 Use of Test BlocksThe test blocks described in thispractice shall not be used for purpos
14、es other than measuring theimpedance of eddy-current probes as specified in this practice.1This practice is under the jurisdiction of ASTM Committee E07 on Nonde-structive Testing and is the direct responsibility of Subcommittee E07.07 onElectromagnetic Method.Current edition approved July 1, 2007.
15、Published July 2007. Originally approvedin 1994. Last previous edition approved in 2001 as E 1629 - 94(2001).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 the sta
16、ndards Document Summary page onthe ASTM website.1Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.They shall not be used for standardizing an examination or fordetermining sensitivity to flaws.5.2 ResponsibilityInitial determination of
17、 the impedancevalues of eddy-current probes shall be performed by the probemanufacturer in accordance with this practice. The results shallbe delivered with the probe and maintained by the organizationusing the probe. While the retesting of probes may be per-formed using this practice, only the resu
18、lts obtained before theprobe is in use should be compared to the initial impedancevalues. The impedance results should not be compared to theinitial values after a probe has been used.6. Specific Practice6.1 Test MethodImpedance measurements shall be madeon an aluminum alloy test block with a machin
19、ed slot thatconforms to the requirements of this practice. The operatingfrequency (as specified by the probe manufacturer) may varyfor each probe examined, depending on the specific probegeometry, required skin depth, matching impedance, desiredsignal strength, and application. A commercial impedanc
20、emeasuring instrument that conforms to 6.1.1 shall be used tomake the measurements. The measurements will be recordedon the worksheet (Appendix X1) to calculate the probeimpedance. The calculated values shall be compared to theacceptable criteria (6.3) to determine probe acceptability.6.1.1 Test Equ
21、ipmentThe test instrument shall be either acommercial impedance measuring instrument or an LCR meterwith an oscillator capable of driving a current in the probe atthe probes operating frequency. The output shall display theprobe impedance in either polar coordinates, providing amagnitude and a phase
22、 angle, or rectangular coordinates,providing resistive and reactive components of the impedance,or both formats, that is, in polar and rectangular coordinates.This instrument shall be certified as having been calibrated inaccordance with the manufacturers specifications, with thecalibration sticker
23、indicating the calibration date and therequired interval or next calibration date.6.1.2 Test BlocksThe test block shall be fabricated from7075-T6 aluminum alloy 1.9-cm (0.75-in.) thick, with slottedholes for testing bolt hole probes and a slotted flat section fortesting surface probes. All test surf
24、aces shall be polished to anaverage finish # 15 m (591 in.). The conductivity of thealuminum alloy should be between 30 and 35 % IACS.6.1.2.1 The slotted flat section shall have side measurementsof at least six times the coil diameter or 5.1 by 5.1 cm (2 by 2in.), whichever is larger. The slot shall
25、 be machined across theblocks surface and shall measure at least 5.0 cm (2-in.) long.The slot cross section shall measure 0.1 6 0.01 mm (0.004 60.0004 in.) wide and 0.5 6 0.025 mm (0.02 6 0.001 in.) deep.6.1.2.2 The test holes shall be made for all of the nominalsizes of bolt hole probes to be exami
26、ned.The edges of the holesshall be spaced 1.9-cm (0.75-in.) apart from each other andfrom the block edges. The slot shall run the entire length of thehole and will be 0.1 6 0.01-mm (0.004 6 0.0004-in.) wide and0.5 6 0.025-mm (0.02 6 0.001-in.) deep.6.1.2.3 Fig. 1 shows a representative test block wi
27、th theholes used for testing two different sizes of bolt hole probes.The length of the block (x + 5.1 cm) depends on the numberand size of the test holes required by the user, as well as theamount of clearance required between each hole and theblocks edges.6.2 Measurement Procedure:6.2.1 Measurement
28、sImpedance values can be expressedin different ways. Impedances are most commonly given ineither rectangular or polar coordinates. In polar form, theimpedance is expressed as a magnitude, |Z|, with a correspond-ing phase angle, u, and often appears as |Z|/ u. In rectangularform the impedance is expr
29、essed as a combination of a resistivecomponent, R, and a reactive or imaginary (denoted by j)component, X. This form often appears as R 6 jX. Fig. 2 showstwo points measured in both forms and the resulting impedancechange (DZ) calculation. This is typical of the way in whichimpedance changes are mea
30、sured on actual eddy-currentprobes using the test method specified in this practice. Theimpedance of a probe is measured first off the slot and then onthe slot in this method, and the difference between these twomeasurements is calculated. An error may occur in the calcu-lations if appropriate coord
31、inate conversions are not made(addition and subtraction are performed in the case of rectan-gular coordinates and multiplication and division in the case ofpolar coordinates).FIG. 1 Representative Test BlockE16290726.2.1.1 All performance tests shall be conducted within thetemperature range from 15
32、to 27C (60 to 80F). The probe testfrequency shall depend on the rated operating frequency of theparticular probe under test (see X1.4.3.3).6.2.2 Probe Impedance in AirAttach the probe to theimpedance measuring instrument, and position the probe atleast 50.8 mm (2 in.) away from any electrically cond
33、uctingmaterial or hardware, or both. Measure the impedance andrecord the impedance values on the worksheet. Compare themeasurement to the values listed in 6.3.1.6.2.3 Average Off-Slot Probe Impedance Place the probeon the surface of or in the hole in the test block, as appropriate.For a surface prob
34、e, place the probe on four different positionson the face of the block. The center of each position shall be atleast four coil diameters from any edge, slot, or hole. For a bolthole probe, rotate the probe face in the hole to four differentpositions that are away from the slot and the top and bottom
35、 ofthe hole. Measure the impedance and record the four imped-ance values on the worksheet in either polar or rectangularcoordinates. If necessary, convert the polar values to RoffandXoff(resistive and reactive components). Calculate the magni-tude of each of the measurements and record them on thewo
36、rksheet. Determine the variation (scatter) in the magnitudesof the measurements as defined in X1.3.1.3 and compare it tothe requirements given in 6.3.2. When acceptable values areobtained, average the four values to calculate Roff avgand Xoffavg. Record the averages on the worksheet.6.2.4 Maximum On
37、-Slot ImpedancePosition the probeface on the slot to obtain a maximum impedance reading.Perform this procedure four times, and record the four resultingimpedances in rectangular coordinates, Ronand Xon, on theworksheet.Average the four values to calculate Ron avgand Xonavg. Record the averages on th
38、e worksheet.6.2.5 Probe Performance CriterionThe probe impedancechange caused by the slot, DZ, is the magnitude of Ron avg Roffavg and Xon avg Xoff avg. The fractional change is the absolutevalue of D Z divided by |Zoff avg|. Appendix X1 contains theformulas for calculating the values of |DZ| and| Z
39、off avg|. Recordthe calculated values on the worksheet and compare them tothe requirements of 6.3.3 to determine acceptance.6.3 Acceptance CriteriaAcceptance of a probe beingcharacterized by this practice requires that it meet all of thefollowing criteria:6.3.1 Probe Impedance in AirUnless otherwise
40、 specified,the magnitude of the probe impedance in air shall be between20 and 1000 V, and the phase shall be between 70 and 90 deg.An impedance value below 20 V indicates the possibility of ashort circuit in the probe coil, and a value above 1000 Vindicates a possible open circuit.6.3.1.1 The magnit
41、ude of the impedance in air shall bewithin 10 % of the value specified for that type of probe by theprobe manufacturer and be within the input impedance rangespecified for the measuring instrument.6.3.2 Measurement ScatterA variation greater than 4 %among the off-slot impedance measurements indicate
42、s that thevalues are too scattered. The measurements must be repeatedusing greater care in holding the surface probe more securelyor fitting the bolt hole probe more snugly in the hole. Repeatedhigh variation indicates that an analysis of the system should beperformed using different examiners or kn
43、own acceptableprobes. The probe is unacceptable if the measurement scattercannot be reduced to the acceptable value.6.3.3 Probe Impedance RatioThese ratios will be deter-mined by agreement between the eddy-current probe manufac-turer and the probe purchaser.7. Keywords7.1 absolute eddy-current probe
44、s; eddy-current probes; im-pedance; nondestructive testingAPPENDIXES(Nonmandatory Information)X1. WORKSHEET FOR CALCULATION OF RESULTSX1.1 GeneralX1.1.1 ScopeThis appendix provides mathematical for-mulas and a worksheet for recording measurements andcalculating results. It is recommended that a blan
45、k worksheetcontaining relevant fields such as identified in X1.4 be pre-pared for recording information and data from measurementsin accordance with this practice, and this blank worksheet bephotocopied for each probe tested. Appendix X2 contains anexample of a completed worksheet.X1.2 General Pract
46、iceX1.2.1 These measurements should be performed using atest instrument that displays impedance in polar or rectangularcoordinates, or both. To perform the necessary calculations,both forms of complex impedance (polar and rectangular) arenecessary. Mathematical conversion will be necessary if thetes
47、t instrument does not display the impedance in both forms.FIG. 2 Rectangular and Polar Coordinates and Resulting DZE1629073X1.2.1.1 Polar to Rectangular ConversionThe conver-sions from polar (|Z| / u) to rectangular (R 6 jX) can beperformed using the following formulas:R 5 |Z| cos u X 5 |Z| sin u (X
48、1.1)The use of a calculator with trigonometric functions (cos andsin) is recommended.X1.2.1.2 Rectangular to Polar ConversionThe conver-sions from rectangular (R6 jX) to polar (|Z| / u) can beperformed using the following formulas:|Z| 5 =R21 X2u5tan1X/R! (X1.2)X1.3 Specific PracticeX1.3.1 It will be
49、 necessary to perform the following calcu-lations after recording the measured impedances:X1.3.1.1 Average Value This involves adding the fourmeasurement values, that is (R1+ R2+ R3+ R4and X1+X2+ X3+ X4), dividing each total by four, and recording thoseresults in the appropriate space on the worksheet (see X1.4.6.1or X1.4.6.2).X1.3.1.2 Impedance Magnitude|Z| 5 = R21 X2.X1.3.1.3 Measurement ScatterA percentage value ob-tained by choosing the highest and lowest values from the fouroff-flaw impedance magnitudes (see 6.2.3) and applying thefo
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