electromagnetic testing q&a 002

Electromagnetic TestingQ&A -001 (without standard answers)

My ASNT Level III Pre-Exam Preparatory Self Study Notes 7th May 2015

Charlie Chong/ Fion Zhang


Petrochemical Applications


http://independent.academia.edu/CharlieChong1http://www.yumpu.com/zh/browse/user/charliechonghttp://issuu.com/charlieccchong

Fion Zhang at Shanghai7th May 2015

http://meilishouxihu.blog.163.com/



REVIEW QUESTIONS without standard answers

http://www.proprofs.com/quiz-school/story.php?title=eddy-current-practise


1. A method of minimizing the effect of indications caused by gradual dimensional changes while retaining the indications caused by discontinuities is to:

A. Include a high pass filter in the eddy current test equipment B. Include a low pass filter in the eddy current test equipment C. Increase the band pass of the amplifier D. Use the impedance method of testing

2. Which of the following methods may be used to improve the signal-to-noise ratio of an eddy current test system?

A. Filtering or differentiation B. Phase discrimination C. Integration D. All 3 are correct

3. In order to decrease the effect on conductivity readings due to variations in test part thickness:

A. The test frequency should be increased B. The test frequency should be decreased C. The fill factor should be decreased D. There is no practical method for decreasing this effect


4. When testing by the eddy current method, discontinuities will be most easily detected when the eddy currents are:

A. Coplanar with the major plane of the discontinuity B. Perpendicular to the major plane of the discontinuity C. Parallel to the major plane of the discontinuity D. 90 degrees out of the phase with current in the coil

5. A term used to describe the effect observed due to a change in the electromagnetic coupling between a test specimen and a probe coil when the distance of separation between them is varied is:

A. Fill factor B. Edge effect C. End effect D. Lift off

6. A term to define the phenomenon where, at very high frequencies, the eddy current flow is restricted to an extremely thin outer layer of the conductor is:

A. Skin effect B. High frequency filtration C. Low frequency filtration D. Any of these answers


7. The fill factor when a 1/2 inch diameter bar is inserted in a 1 inch diameter coil is: A. 0.5 (50%) B. 0.75 (75%) C. 1.0 (100%) D. 0.25 (25%)

8. The term used to define the difference between actual instrument output and expected output as defined by a straight line calibration curve is:

A. Phase shift B. Nonlinearity C. Lift off D. Skin effect

9. Which of the following could be used to suppress unwanted high frequency harmonics?

A. Low pass filter B. Oscillator C. Phase discriminator D. High pass filter


10. The impedance change of an eddy current test coil due to a change in the test part characteristics can be most easily analyzed as a combined change in:

A. Capacitive reactance and resistance B. Harmonic frequencies and inductive reactance C. Signal amplitude and phaseD. Retentivity harmonic frequencies

11. The inductive reactance of a test coil can be calculated using the formula:A. Xr = 2 pie LB. Xr = 1/2 pie L C. Xr = 2 pie fLD. Xr = 1R

12. When conducting an eddy current test, variations in the test material can be detected as variations in:

A. Test speed B. Impedance of the pickup coil C. None of the 2 answers D. Both answers are correct


13. A term used to define 2 or more coils electrically connected in opposition such that any electromagentic condition which is not common to both a test specimen and a reference specimen will produce an unbalance in the system is:

A. Differential B. Absolute C. Laminar D. Flying probes

14. Tubing is generally inspected using: A. U-Shaped coils B. Gap coils C. Encircling coils D. None of the answers

15. When testing small parts in an eddy current encircling coil for permeability measurements, which of the following test parameters may be considered important?

A. Length of the test sample B. Thickness of the test sample C. Cross-sectional area of the test sample D. All answers are correct


16. In a test coil consisting of both a primary and secondary winding, the voltage across the secondary is a function of:

A. Test material permeability B. Test frequency C. Geometry of the test object D. All answers are correct

17. Eddy current testing relies on the principle of: A. Magnetostriction B. Electromagnetic induction C. Piezoelectric energy conversion D. Magnetomotive force

18. When the H field strength around a material is increased and then decreased to zero, the induction field B within the part does not return to zero, the term to define this B value when H has returned to zero is:

A. Coercive force B. Residual Magnetism C. Saturation value D. Hysteresis loss


19. The term used to define the value of H field required to decrease the remanence of a material to zero is:

A. Coercive force B. Magnetizing force C. Back emf D. The overlap value

20. The 3 major specimen parameters which influence eddy current testing are: A. Electrical conductivity, frequency, and material geometry B. Density, permeability, and frequency C. Electrical conductivity, permeability, and material geometryD. Thermal conductivity, electrical conductivity, and permeability

21. Doubling the number of turns on a coil will: A. Double the inductance B. Halve the inductance C. Decrease the inductance by a factor of 4 D. Increase the inductance by a factor of 4


22. Frequency ratio f/f can be defined as:A. The argument of the mathematical function describing the electromagnetic field

within the test specimenB. Test frequency divided by limit frequencyC. NeitherD. Both

23. When testing tubing, using an encircling (OD) coil, What is the phase relationshipof the output signals from identical ID and OD discontinuities?A. The signals are in phaseB. The phase of the OD discontinuity leads the phase of the ID discontinuityC. The phase of the OD discontinuity lags the phase of the ID discontinuityD. Indeterminate

24. A term used to define an instrumentation technique which discriminatesbetweenvariables in the test part by the different phase angle changes which theseconditions produce in the test signal is:A. Phase distortionB. Phase shiftingC. Phase discriminationD. Phase analysis


Phase Lag Phase lag is a parameter of the eddy current signal that makes it possible to obtain information about the depth of a defect within a material. Phase lag is the shift in time between the eddy current response from a disruption on the surface and a disruption at some distance below the surface. The generation of eddy currents can be thought of as a time dependent process, meaning that the eddy currents below the surface take a little longer to form than those at the surface. Disruptions in the eddy currents away from the surface will produce more phase lag than disruptions near the surface. Both the signal voltage and current will have this phase shift or lag with depth, which is different from the phase angle discussed earlier. (With the phase angle, the current shifted with respect to the voltage.)Phase lag is an important parameter in eddy current testing because it makes it possible to estimate the depth of a defect, and with proper reference specimens, determine the rough size of a defect. The signal produced by a flaw depends on both the amplitude and phase of the eddy currents being disrupted. A small surface defect and large internal defect can have a similar effect on the magnitude of impedance in a test coil. However, because of the increasing phase lag with depth, there will be a characteristic difference in the test coil impedance vector.Phase lag can be calculated with the following equation. The phase lag angle calculated with this equation is useful for estimating the subsurface depth of a discontinuity that is concentrated at a specific depth. Discontinuities, such as a crack that spans many depths, must be divided into sections along its length and a weighted average determined for phase and amplitude at each position below the surface.

ϴ = x/ δ radian

Where: ϴ =Phase Lag (Radian or Degrees)x=Distance Below Surface (in or mm)δ =Standard Depth of Penetration (in or mm)

https://www.nde-ed.org/EducationResources/CommunityCollege/EddyCurrents/Physics/phaselag.htm


25. If the characteristic frequency (fq) of a material is 125 hz, the test frequencyrequired to give an f/fq ratio of 10 would be:A. 1.25 HzB. 12.5 HzC. 1.25 kHzD. 12.5 kHz

26. At a fixed test frequency, in which of the following materials will the eddycurrent penetration be greatest?A. Aluminum (35% IACS conductivity)B. Brass (15% IACS conductivity)C. Copper (95% IACS conductivity)D. Lead (7% IACS conductivity)

27. The heating effect in magnetic materials caused by work required to rotatemagnetic domains can be eliminated by:A. Increasing the rate of displacement of the specimen through the coilB. Magnetically saturating the test specimenC. Decreasing the rate of displacement of the test specimen throughthe test coilD. Testing in an air-conditioned room


28. A term used to define any change in a sinusoidal signal when the output is not alinear reproduction of the input is:A. DistortionB. LinearityC. Phase shiftingD. Dynamic range

29. If the test frequency increases while field strength is held constant, thesurface density eddy currentA. DecreasesB. IncreasesC. Remains the sameD. Could do any of the 3 answers

30. As the fill factor decreases, the impedance variation of a pickup coil produced by agiven change in conductivity will:A. IncreaseB. Remain the sameC. DecreaseD. Could do any of the 3


31. Which of the following would be easier to detect in tubing by the eddycurrent method using self comparison differential coil arrangement?A. Gradual changes in diameterB. Gradual changes in conductivityC. Changes in temperatureD. Short flaws

32. The magnetic domains in an unmagnetized ferromagnetic material are:A. Arranged to facilitate the condition of electronsB. Randomly oriented and neutralize each otherC. Uniformly orientedD. Create a major north and south pole in the material

33. When a magnetic material is placed in a region of an applied magnetizingforce(H), magnetic field (B) is developed in the material by means of:A. InductionB. ConductionC. Heat transferD. Magnetic domain transfer


34. To eliminate any dependence upon the number of turns of a test coil, theinductance values of an impedance diagram are:A. DisregardedB. NormalizedC. Corrected to a value of 1D. None of the 3 answers

35. A term used to define a system which indicates only the magnitude of variationsin the total coil impedance regardless of the phase or direction in which it occurson an impedance plane is:A. Inductive reactance magnitude systemB. Feedback-controlled systemC. Impedance-magnitude systemD. Impedance vector analysis system

36. When eddy current testing tubing with a system that includes a frequencydiscriminating circuit,which of the following variables wolud be classified as ahigh frequency variable?A. Small discontinuitiesB. Conductivity changesC. Diameter changesD. Wall thickness variations


37. A major problem associated with eddy current test method is the:A. Inability of eddy current testing to accurately measure conductivityB. Need to test at low speeds to prevent skippingC. Large number of known or unknown variables which appear in the output

indicationD. Inability of eddy current testing to detect small discontinuities

38. The atoms of a metal showing magnetic characteristics are grouped into regionswhich are the smallest known permanent magnets. These regions are called:A. Lattice structuresB. CellsC. DomainsD. Planetary spins

39. When a coil's magnetizing force is applied to a ferromagnetic material, the fluxdensityin the material is:A. Less than the flux density generated by the test coil because of heat lossesB. Less than the flux density generated by the test coil because of resistivityC. The same as the flux density generated by the test coilD. Greater than the flux density generated by the test coil


40. The flux density in a magnetic material is usually designated by the :A. Symbol uB. Symbol oC. Letter BD. Letter H

41. The magnetizing force of an eddy current test coil is usually designated by the:A. Symbol uB. Symbol oC. Letter BD. Letter H

42. In eddy current testing, the specimen is coupled to the test coil by:A. Core couplingB. Magnetic saturationC. The coil's magnetic fieldD. Magnetic domains


43. The thickness of nonconductive coatings on a conductive base can be most simplymeasuredby:A. Observing the lift-off effect caused by the coatingB. Testing both sides of the specimenC. Varying the current in the test coilD. Varying the test frequency over a given range during the test

44. The use of magnetic shielding around the exciting coil will generally:A. Increase the magnetic field extension but decrease the eddy current penetrationB. Increase the magnetic field extension and eddy current penetrationC. Decrease the magnetic field extension but increase the eddy current

penetrationD. Decrease the magnetic field extension and eddy current penetration

45. Which of the following is not a factor that affects the inductance of an eddycurrent test coil?A. Diameter of coilsB. Test frequencyC. Overall shape of the coilsD. Distance from other coils


46. The formula used to calculate the impedance of an eddy current test coil is:A. Z = 2 pie flB. Z = X,+RC. Z = the square root X,+RD. Z = the square root X, to the 2nd power+R to the 2nd power

47. An out-of-phase condition between current and voltage:A. Can exist only in the primary winding of an eddy current coilB. Can exist only in the secondary winding of an eddy current coilC. Can exist in both the primary and secondary windings of an eddy current coilD. Exist only in the test specimen

48. A term used to define a surface coil mounted so that the coil can be rotated aboutthe circumference of a test specimen is:A. Bobbin coilB. Encircling coilC. Spinning coilD. Gap coil


49. A term used to define an eddy current test coil which uses magnetic material topurposely shape the magnetic field is:A. Bobbin coilB. Encircling coilC. Spinning coilD. Gap coil ?

50. The vector-point, ellipse, and linear time-base methods are all subdivisions of the:A. Impedance method of testingB. The modulation analysis method of testingC. The phase analysis method of testingD. None of these are correct

51. It is frequently possible to separate the conductivity variable from thepermeability and dimensional variables when using:A. The vector-point method of testingB. The ellipse method of testingC. The linear time-base method of testingD. Any of these methods of testing


52. When eddy current testing by the ellipse method, the normal indication when thetest specimen and reference standard are the same is approximately:A. A straight horizontal line on the cathode tubeB. An ellipse method of testingC. A null reading on a meterD. A clean base line on a strip chart

53. When eddy current testing by ellipse method, one variable may be indicated bythe angleof the ellipse or straight line while another variable may be indicated bythe:A. Brightness of the ellipseB. Horizontal length of the straight lineC. Size of the ellipse openingD. Sinusoidal shape of the waveform

54. When eddy current testing by the linear time base method, what is applied to thevertical deflection plates of a cathod ray tube when the test specimen and referencestandard are the same and the balance controls are properly adjusted?A. A sinusoidal wave in phase with the timing voltage ?B. A sinussoidal wave 90 degrees out of phase with the timing voltageC. A sawtooth waveformD. Zero net voltage


55. When eddy current testing by the linear time-base method, what is applied to thevertical deflection plates of a cathode ray tube when a condition of unbalance existbetween the test specimen and the reference standard?A. A sinusoidal waveB. A sawtooth waveC. A squarewaveD. No voltage

56. The conductivity value for a metal is a function of the :A. Heat treatment given the metalB. Cold working performed on the metalC. Aging process used on the metalD. All of the answers

57. The ratio of the specific diameter of a probe to the minimum discontinuity ofinterest should be:A. Less than 2B. Greater than 2C. Greater than 4D. Greater than 10


58. Which of the following materials would be more likely used as a mountingmaterial for a probecoil?A. AluminumB. FiberglassC. CopperD. Steel

59. A term used to define a surface or internal rupture which is attributed toprocessing at low a temperature or excessive working or metal movement duringthe forging, rolling, or extruding operation is:A. Cold shutB. Micro shrinkageC. BurstD. Inclusion

60. A term used to define the timing relationship invovled in alternating currentsignals is:A. MagnitudeB. PhaseC. ImpedanceD. Reactance


61. When eddy current testing a nonferrous material, the choice of test frequency isdeterminedby the :A. Degree of phase discrimination requiredB. Eddy current penetration neededC. Rate of response requiredD. All of these

62. When testing ferrous materials, a small but detectable portion of the magnetic fluxin the material will pass outside the metal when a surface discontinuity isencountered. This flux iscalled:A. Air fluxB. Leakage fluxC. Induced fluxD. None of these

63. A term to define a property of a test system which enables the separation ofsignals due to discontinuities in the test specimen that are located in closeproximity to each other is:A. Dynamic rangeB. SensitivityC. LinearityD. Discontinuity resolution


64. A term used to define a material having a permeability less than that of a vacum isA. MagneticB. DiamagneticC. FerromagneticD. Paramagnetic

65. The inductive reactance of a coil is measured in units of:A. MhosB. OhmsC. Henry'sD. Gauss

66. Which of the following coil arrangements would eliminate or decrease the effectsof minor variations in diameter, chemical composition, hardness, etc, which occurgradually along the length of a wire?A. External reference differentialB. Self-comparison differentialC. Single coil absoluteD. Double coil absolute


67. Which of the following conditions is not important when selecting specimens to be used as reference standards?A. The specimen should be of the same size and shape as the piece to be testedB. The specimen should have the same heat treatment as the piece to be testedC. The surface finish of the specimen should be the same as the piece to be testedD. If the material is aluminum, the surface should be anodized

68. An eddy current test coil's magnetic field intensity in air:A. Increases with distance outside the coil and varies across the diameter inside the coilB. Decreases with distance outside the coil and varies across the diameter inside the coilC. Decreases with distance outside the coil and is assumed to be constant across the

diameter inside the coilD. Increases with distance outside the coil and is assumed to be constant across the diameter

inside the coil

69. The circuits which make it possible to minimize the effect of signals caused by variables of no interest on the readout mechanism are based on differences in:A. AmplitudeB. PhaseC. FrequencyD. Any one or a combination of the quantities listed above


70. When a nonmagnetic rod is placed inside an eddy current test coil:A. The magnetic field generated by the coil is increased in intensityB. The distribution of eddy currents is uniform through the rod's cross sectionC. The distribution of eddy currents is at a maximum at the rod's surface, or

near the surface,and decreases to essentially zero at the rod's centerD. The temperature of the rod decreases

71. The symbol commonly used to signify impedance is:A. ZB. X; EC. RD. Xc

72. A decrease in conductivity is equivalent to:A. An increase in permeabilityB. An increase in resistivityC. A decrease in permeabilityD. A decrease in resistivity


73. If the conductivity of a test part in an eddy current test coil decreases, themagnitudeof the eddy currents at a given depth in the test specimen:A. IncreasesB. Remains the sameC. DecreasesD. May increase or decrease

74. When the voltage applied to a circuit and the current through the circuit both reachtheir maximums and minimums at the same time, the voltage and current are:A. AdditiveB. In phaseC. RegenerativeD. Out of phase

75. Which of the following is not a commonly used eddy current testing readoutmechanism?A. Signal generatorB. MeterC. Cathode ray tubeD. Strip-chart recorder


76. Which of the following materials would have the highest resistivity value?A. Aluminum with a 42% IACS ratingB. Magnesium with a 37% IACS ratingC. Cast steel with a 10.7% IACS ratingD. Zirconium with a 3.4% IACS rating

77. The ratio of a material's flux density to a test coil's magnetizing force,(B/H), canbeused to determine the material's:A. ConductivityB. ResistivityC. Lift-offD. Permeability

78. The magnetic field generated by eddy currents induced in a test specimen:A. Opposes the magnetic field that induced the eddy currentsB. Reinforces the magnetic field that induced the eddy currentsC. Cancels the magnetic field that induced the eddy currentsD. Has no effect on the magnetic field that induced the eddy currents


79. The impedance of a test coil usually can be represented by the vector sum of:A. Inductive reactance and resistanceB. Capacitive reactance and resistanceC. Inductive reactance and capacitive reactanceD. Inductance and capacitance

80. For age hardenable aluminum and titanium alloys, changes in hardness areindicated bychanges in:A. RententivityB. PermeabilityC. Conductivity (?)D. Magnetostriction

81. The penetration of eddy currents in a conductive material is decreased when:A. Test frequency or conductivity of the specimen is decreasedB. Test frequency is decreased or conductivity of the specimen is increasedC. Test frequency, conductivity of the specimen or permeability of the specimenare increasedD. Permeability of the specimen is decreased


82. When the electrical current in an eddy current coil reverses direction:A. The direction of the eddy currents in a part remains the sameB. The eddy currents in the test part will change phase 45 degreesC. The direction of the eddy currents in the part also reversesD. The eddy currents in the part remain the same

83. When testing magnetic materials in a ac field, increasing the field strength:A. Has no effectB. Increases eddy current penetrationC. Decreases eddy current penetrationD. Decreases eddy current penetration to some minimum value, and then increases it to its maximum value when the specimen becomes magnetically saturated

84. Impedance diagrams have been mathematically derived and experimentally verified formaterialsof any conductivity and permeability having rectangular, cylindrcal, or sphericalsymmetry. To test all specimens of similar geometry under the same condition, it is onlynecessary to choose a test frequency, (f), so that frequency ratio f/f lies at the same point on the impedance diagram for each specimen. This principle is based upon:A. Ohm's lawB. Kirchoff's lawC. The Similarity LawD. None of these


Kirchhoff's circuit laws are two equalities that deal with the current and potential difference (commonly known as voltage) in the lumped element model of electrical circuits. They were first described in 1845 by German physicist Gustav Kirchhoff.[1] This generalized the work of Georg Ohm and preceded the work of Maxwell. Widely used in electrical engineering, they are also called Kirchhoff's rules or simply Kirchhoff's laws. Both of Kirchhoff's laws can be understood as corollaries of the Maxwell equations in the low-frequency limit. They are accurate for DC circuits, and for AC circuits at frequencies where the wavelengths of electromagnetic radiation are very large compared to the circuits.

This law is also called Kirchhoff's first law, Kirchhoff's point rule, or Kirchhoff's junction rule (or nodal rule). The principle of conservation of electric charge implies that:At any node (junction) in an electrical circuit, the sum of currents flowing into that node is equal to the sum of currents flowing out of that node or equivalentlyThe algebraic sum of currents in a network of conductors meeting at a point is zero.

http://en.wikipedia.org/wiki/Kirchhoff%27s_circuit_laws


Short research about the history of eddy currentThe first person to observe current eddies was François Arago (1786-1853), the 25th president of France, Who was also a mathematician, physicist and astronomer.1824 He discovered what has been called rotatory magnetism, and the fact that most bodies could be magnetized; these discoveries were completed and explained by Michael Faraday (1791-1867).In 1834, Heinrich Lenz stated the principle that defines how the properties of the test objects are communicated back to the test system. Lenz's law states that the direction of current flow in the test object will be such that its magnetic field will oppose the magnetic field that caused the current flow in the test object. This means, in practice, the eddy currents communicate with the test coil by developing secondary flux that cancels a portion of the coil's flux equivalent to the magnitude and phase of the flux developed by the eddy currents.

However, the first person who really discovered eddy current (or Foucault current) was the French physicist Léon Foucault (1819-1868). In September, 1855, he discovered that the force required for the rotation of a copper disc becomes greater when it is made to rotate with its rim between the poles of a magnet, the disc at the same time becoming heated by the eddy current induced in the metal.

The first use of eddy current for NDT occurred in 1879 when D. E. Hughes used the principles to conduct metallurgical sorting tests.The development of the eddy current method progressed slowly until the late 1940s, when Dr. Friedreich Foester found the Institute Dr. Foerster, which made great strides in developing and marketing practical eddy current test instruments. by the late 1960s the institute had developed a product line covering virtually every application of the eddy current test method and worked with American manufacturers to firmly establish the method in the US. Two major contributions of Foerster were development of impedance plane display, which greatly aided in communication of test information to the user, and formulation of the law of similarity, which enables the practitioner to duplicate the same eddy current performance under a variety of test situations.

http://ndt-review.blogspot.com/2010/12/eddy-current-method-short-research.html


85. To be useful, limit frequency equations must be:A. Used with their impedance diagramsB. Used to determine their impedance diagramsC. Both of theseD. Neither of these

86. When a rod is placed in an encircling type of coil, the density of eddy currentswill be greatest:A. At the surfaceB. At the centerC. Midway between the surface and centerD. None of these

87. term fill factor applies to:A. A surface coilB. Coaxial cableC. A encircling coilD. All of these


88. An eddy current system using handling equipment with automatic marking of thedefective areas primarily makes it possible to:A. Remove defective areas of the product, if desiredB. Eliminate test surface contaminationC. Allow an inexperienced operator to establish the defect causeD. Pass rejectable material

89. 2 TEST COILS ARE OFTEN USED IN A BRIDGE CIRCUITA. Eliminate skin effectB. Determine the differences between a known standard sampleC. Increase the conductivity of the circuitD. Decreases the system sensitivity

90. In inspecting ferromagnetic materials, relatively low frequencies are normallyused becauseof the:A. Low penetrability of these materialsB. Higher resolutionC. Lower resolutionD. Higher penetrability of these materials


91. The actual frequency used in any specific eddy current inspection should beselectedon the basis of the:A. Thickness of the materialB. Desired depth of penetrationC. Degree of sensitivity or resolution requiredD. Purpose of the inspectionE. All of these

92. In modulation analysis testing, which of the following would not modulate thetest frequency applied to the test coil?A. Discontinuities in the test specimenB. Dimension changes of the test specimenC. Chemical composition of the test specimenD. A filter in the test circuit


Good Luck


More Readinghttp://www.ndt.net/article/ecndt02/322/322.htmhttp://www.proprofs.com/quiz-school/story.php?title=eddy-current-practise


Further Reading


Good Luck

Charlie Chong/ Fion Zhanghttps://www.yumpu.com/en/browse/user/charliechong

1. A method of minimizing the effect of indications caused by gradual dimensional changes whileretaining the indications caused by discontinuities is to:

A. Include a high pass filter in the eddy current test equipmentB. Include a low pass filter in the eddy current test equipmentC. Increase the band pass of the amplifierD. Use the impedance method of testing

2. Which of the following methods may be used to improve the signal-to-noise ratio of an eddycurrent test system?

A. Filtering or differentiation B. Phase discrimination C. IntergrationD. All 3 are correct

3. In order to decrease the effect on conductivity readings due to variations in test part thickness:

A. The test frequency should be increasedB. The test frequency should be decreasedC. The fill factor should be decreasedD. There is no practical method for decreasing this effect

4. When testing by the eddy current method, discontinuities will be most easily detected when the eddy currents are:

A. Coplanar with the major plane of the discontinuityB. Perpendicular to the major plane of the discontinuityC. Parallel to the major plane of the discontinuityD. 90 degress out of the phase with current in the coil

5. A term used to describe the effect observed due to a change in the electromagnetic coupling between a test specimen and a probe coil when the distance of separation between themis varied is:

A. Fill factorB. Edge effect C. End effect D. Lift off

6. A term to define the phenomenon where, at very high frequencies, the eddy current flow is resrticted to an extremely thin outer layer of the conductor is:

A. Skin effect B. High frequency filtrationC. Low frequency filtration D. Any of these answers

7. The fill factor when a 1/2 inch diameter bar is inserted in a 1 inch diameter coil is:A. 0.5 (50%)B. 0.75 (75%)C. 1.0 (100%)D. 0.25 (25%)

8. The term used to define the difference between actual instrument output and expectedoutput as defined by a straight line calibration curve is:

A. Phase shiftB. NonlinearityC. Lift off D. Skin effect

9. Which of the following could be used to suppress unwanted high frequency harmonics?

A. Low pass filterB. OscillatorC. Phase discriminatorD. High pass filter

10. The impedance change of an eddy current test coil due to a change in the test partcharacteristics can be most easily analyzed as a combined change in:

A. Capacitive reactance and resistanceB. Harmonic frequencies and inductive reactanceC. Signal ampllitude and phaseD. Retentivity harmonic frequencies

11. The inductive reactance of a test coil can be calculated using the formula: A. Xr = 2 pie LB. Xr = 1/2 pie L C. Xr = 2 pie fLD. Xr = 1R

12. When conducting an eddy current test, variations in the test material can be detectedas variations in:

A. Test speedB. Impedance of the pickup coilC. None of the 2 answersD. Both answers are correct

13. A term used to define 2 or more coils electrically connected in opposition such that any electromagentic condition which is not common to both a test specimen and areference specimen will produce an unbalance in the system is:

A. DifferentialB. AbsoluteC. Laminar D. Flying probes

14. Tubing is generally inspected using:A. U-Shaped coilsB. Gap coilsC. Encircling coilsD. None of the answers

15. When testing small parts in an eddy current encircling coil for permeability measurements,which of the following test parameters may be considered important?

A. Length of the test sample B. Thickness of the test sampleC. Cross-sectional area of the test sampleD. All answers are correct

16. In a test coil consisting of both a primary and secondary winding, the voltage across thesecondary is a function of:

A. Test material permeabilityB. Test frequencyC. Geometry of the test objectD. All answers are correct

17. Eddy current testing relies on the principle of: A. MagnetostrictionB. Electromagnetic inductionC. Piezoelectric energy conversionD. Magnetomotive force

18. When the H field strength around a material is increased and then decreased to zero,the induction field B within the part does not return to zero, the term to define this Bvalue when H has returned to zero is:

A. Coercive forceB. Residual Magnetism C. Saturation valueD. Hysteresis loss

19. The term used to define the value of H field required to decrease the remanence of a material to zero is:

A. Coercive forceB. Magnetizing forceC. Back emf D. The overlap value

20. The 3 major specimen parameters which influence eddy current testing are: A. Electrical conductivity, frequency, and material geometryB. Density, permeability, and frequencyC. Electrical conductivity, permeability, and material geometryD. Thermal conductivity, electrical conductivity, and permeability

21. Doubling the number of turns on a coil will:A. Double the inductanceB. Halve the inductance C. Decrease the inductance by a factor of 4D. Increase the inductance by a factor of 4

22. Frequency ratio f/f can be defined as:A. The argument of the mathematical function describing the electromagnetic field

within the test specimen B. Test frequency divided by limit frequencyC. NeitherD. Both

23. When testing tubing, using an encircling (OD) coil, What is the phase relationship of the output signals from identical ID and OD discontinuities?

A. The signals are in phaseB. The phase of the OD discontinuity leads the phase of the ID discontinuity C. The phase of the OD discontinuity lags the phase of the ID discontinuityD. Indeterminate

24. A term used to define an instrumentation technique which discriminates betweenvariables in the test part by the different phase angle changes which these conditionsproduce in the test signal is:

A. Phase distortionB. Phase shifting C. Phase discrimination D. Phase analysis

25. If the characteristic frequency (fq) of a material is 125 hz, the test frequency required to give an f/fq ratio of 10 would be:

A. 1.25 HzB. 12.5 Hz C. 1.25 kHzD. 12.5 kHz

26. At a fixed test frequency, in which of the following materials will the eddy currentpenetration be greatest?

A. Aluminum (35% IACS conductivity)B. Brass (15% IACS conductivity)C. Copper (95% IACS conductivity)D. Lead (7% IACS conductivity)

27. The heating effect in magnetic materials caused by work required to rotate magneticdomains can be eliminated by:

A. Increasing the rate of displacement of the specimen through the coilB. Magnetically saturating the test specimenC. Decreasing the rate of displacement of the test specimen throughthe test coilD. Testing in an air-conditioned room

28. A term used to define any change in a sinusoidal signal when the output is not a linearreproduction of the input is:

A. DistortionB. Linearity C. Phase shiftingD. Dynamic range

29. If the test frequency increases while field strength is held constant, the surface density:eddy current

A. DecreasesB. IncreasesC. Remains the same D. Could do any of the 3 answers

30. As the fill factor decreases, the impedance variation of a pickup coil producedby a given chaange in conductivity will:

A. IncreaseB. Remain the same C. DecreaseD. Could do any of the 3

31. Which of the following would be easier to detect in tubing by the eddy currentmethod using self comparison differential coil arrangement?

A. Gradual changes in diameterB. Gradual changes in conductivityC. Changes in temperatureD. Short flaws

32. The magnetic domains in an unmagnetized ferromagnetic material are:A. Arranged to facilitate the condition of electronsB. Randomly oriented and neutralize each otherC. Uniformly orientedD. Create a major north and south pole in the material

33. When a magnetic material is placed in a region of an applied magnetizing force(H), magnetic field (B) is developed in the material by means of:

A. InductionB. ConductionC. Heat transferD. Magnetic domain transfer

34. To eliminate any dependence upon the number of turns of a test coil, the inductancevalues of an impedance diagram are:

A. DisregardedB. NormalizedC. Corrected to a value of 1 D. None of the 3 answers

35. A term used to define a system which indicates only the magnitude of variations in the totalcoil impedance regardless of the phase or direction in which it occurs on an impedance plane is:

A. Inductive reactance magnitude systemB. Feedback-controlled systemC. Impedance-magnitude systemD. Impedance vector analysis system

36. When eddy current testing tubing with a system that includes a frequency discriminating circuit,which of the following variables wolud be classified as a high frequency variable?

A. Small discontinuitiesB. Conductivity changesC. Diameter changesD. Wall thickness variations

37. A major problem associated with eddy current test method is the:A. Inability of eddy current testing to accurately measure conductivity B. Need to test at low speeds to prevent skippingC. Large number of known or unknown variables which appear in the

output indication D. Inability of eddy current testing to detect small discontinuities

38. The atoms of a metal showing magnetic characteristics are grouped into regions whichare the smallest known permanent magnets. These regions are called:

A. Lattice structuresB. CellsC. Domains D. Planetary spins

39. When a coil's magnetizing force is applied to a ferromagnetic material, the flux densityin the material is:

A. Less than the flux density generated by the test coil because of heat losses

B. Less than the flux density generated by the test coil because of resistivity C. The same as the flux density generated by the test coilD. Greater than the flux density generated by the test coil

40. The flux density in a magnetic material is usually designated by the :A. Symbol u B. Symbol o C. Letter B D. Letter H

41. The magnetizing force of an eddy current test coil is usually designated by the:A. Symbol u B. Symbol o C. Letter--BD. Letter--H

42. In eddy current testing, the specimen is coupled to the test coil by: A. Core couplingB. Magnetic saturationC. The coil's magnetic field D. Magnetic domains

43. The thickness of nonconductive coatings on a conductive base can be most simply measuredby:

A. Observing the lift-off effect caused by the coatingB. Testing both sides of the specimenC. Varying the current in the test coilD. Varying the test frequency over a given range during the test

44. The use of magnetic shielding around the exciting coil will generally:A. Increase the magnetic field extension but decrease the eddy current penetrationB. Increase the magnetic field extension and eddy current penetrationC. Decrease the magnetic field extension but increase the eddy current

penetration D. Decrease the magnetic field extension and eddy current penetration

45. Which of the following is not a factor that affects the inductance of an eddy current test coil?

A. Diameter of coilsB. Test frequencyC. Overall shape of the coilsD. Distance from other coils

46. The formula used to calculate the impedance of an eddy current test coil is: A. Z = 2 pie flB. Z = X,+R C. Z = the square root X,+RD. Z = the square root X, to the 2nd power+R to the 2nd power

47. An out-of-phase condition between current and voltage:A. Can exist only in the primary winding of an eddy current coilB. Can exist only in the secondary winding of an eddy current coil C. Can exist in both the primary and secondary windings of an eddy current coil D. Exist only in the test specimen

48. A term used to define a surface coil mounted so that the coil can be rotated about the circumference of a test specimen is:

A. Bobbin coilB. Encircling coil C. Spinning coilD. Gap coil

49. A term used to define an eddy current test coil which uses magnetic material to purposelyshape the magnetic field is:

A. Bobbin coilB. Encircling coil C. Spinning coilD. Gap coil

50. The vector-point, ellipse, and linear time-base methods are all subdivisions of the: A. Impedance method of testingB. The modulation analysis method of testingC. The phase analysis method of testingD. None of these are correct

51. It is frequently possible to separate the conductivity variable from the permeability anddimensional variables when using:

A. The vector-point method of testingB. The ellipse method of testingC. The linear time-base method of testingD. Any of these methods of testing

52. When eddy current testing by the ellipse method, the normal indication when the test specimen and reference standard are the same is approximately:

A. A straight horizontal line on the cathode tubeB. An ellipse method of testingC. A null reading on a meterD. A clean base line on a strip chart

53. When eddy current testing by ellipse method, one variable may be indicated by the angleof the ellipse or straight line while another variable may be indicated by the:

A. Brightness of the ellipseB. Horizontal length of the straight lineC. Size of the ellipse openingD. Sinusoidal shape of the waveform

54. When eddy current testing by the linear time base method, what is applied to the verticaldeflection plates of a cathod ray tube when the test specimen and reference standard arethe same and the balance controls are properly adjusted?

A. A sinusoidal wave in phase with the timing voltageB. A sinussoidal wave 90 degrees out of phase with the timing voltageC. A sawtooth waveform D. Zero net voltage

55. When eddy current testing by the linear time-base method, what is applied to the verticaldeflection plates of a cathode ray tube when a condition of unbalance exist between the test specimen and the reference standard?

A. A sinusoidal waveB. A sawtooth waveC. A squarewaveD. No voltage

56. The conductivity value for a metal is a function of the : A. Heat treatment given the metalB. Cold working performed on the metalC. Aging process used on the metalD. All of the answers

57. The ratio of the specific diameter of a probe to the minimum discontinuity of interest should be:

A. Less than 2B. Greater than 2C. Greater than 4D. Greater than 10

58. Which of the following materials would be more likely used as a mounting material for a probecoil?

A. Aluminum B. FiberglassC. CopperD. Steel

59. A term used to define a surface or internal rupture which is attributed to pprocessingat low a temperature or excessive working or metal movement during the forging, rolling, or extruding operation is:

A. Cold shutB. Micro shrinkageC. BurstD. Inclusion

60. A term used to define the timing relationship invovled in alternating current signals is:

A. MagnitudeB. PhaseC. Impedance D. Reactance

61. When eddy current testing a nonferrous material, the choice of test frequency is determinedby the :

A. Degree of phase discrimination requiredB. Eddy current penetration neededC. Rate of response required D. All of these

62. When testing ferrous materials, a small but detectable portion of the magnetic flux in the material will pass outside the metal when a surface discontinuity is encountered. This flux iscalled:

A. Air fluxB. Leakage fluxC. Induced fluxD. None of these

63. A term to define a property of a test system which enables the separation of signals dueto discontinuities in the test specimen that are located in close proximity to each other is:

A. Dynamic range B. SensitivityC. LinearityD. Discontinuity resolution

64. A term used to define a material having a permeability less than that of a vacum is A. MagneticB. DiamagneticC. FerromagneticD. Paramagnetic

65. The inductive reactance of a coil is measured in units of:A. MhosB. Ohms C. Henry's D. Gauss

66. Which of the following coil arrangements would eliminate or decrease the effects of minor variations in diameter, chemical composition, hardness, etc, which occur gradually along the length of a wire?

A. External reference differentialB. Self-comparison differentialC. Single coil absoluteD. Double coil absolute

67. Which of the following conditions is not important when selecting specimens to be usedas reference standards?

A. The specimen should be of the same size and shape as the pieceto be tested

B. The specimen should have the same heat treatment as the piece to be testedC. The surface finish of the specimen should be the same as the piece to be testedD. If the material is aluminum, the surface should be anodized

68. An eddy current test coil's magnetic field intensity in air:A. Increases with distance outside the coil and varies across the diameter inside the

coil B. Decreases with distance outside the coil and varies across the diameter inside

the coil C. Decreases with distance outside the coil and is assumed to be constant across

the diameter inside the coil D. Increases with distance outside the coil and is assumed to be

constant across the diameter inside the coil

69. The circuits which make it possible to minimize the effect of signals caused by variablesof no interest on the readout mechanism are based on differences in:

A. AmplitudeB. PhaseC. FrequencyD. Any one or a combination of the quantities listed above

70. When a nonmagnetic rod is placed inside an eddy current test coil:A. The magnetic field generated by the coil is increased in intensityB. The distribution of eddy currents is uniform through the rod's cross sectionC. The distribution of eddy currents is at a maximum at the rod's surface, or near

the surface,and decreases to essentially zero at the rod's center

D. The temperature of the rod decreases

71. The symbol commonly used to signify impedance is: A. Z B. X; E C. R D. Xc

72. A decrease in conductivity is equivalent to:A. An increase in permeabilityB. An increase in resistivity C. A decrease in permeabilityD. A decrease in resistivity

73. If the conductivity of a test part in an eddy current test coil decreases, the magnitudeof the eddy currents at a given depth in the test specimen:

A. IncreasesB. Remains the same C. DecreasesD. May increase or decrease

74. When the voltage applied to a circuit and the current through the circuit both reach theirmaximums and minimums at the same time, the voltage and current are:

A. AdditiveB. In phaseC. RegenerativeD. Out of phase

75. Which of the following is not a commonly used eddy current testing readout mechanism?

A. Signal generatorB. Meter C. Cathode ray tubeD. Strip-chart recorder

76. Which of the following materials would have the highest resistivity value?A. Aluminum with a 42% IACS ratingB. Magnesium with a 37% IACS ratingC. Cast steel with a 10.7% IACS ratingD. Zirconium with a 3.4% IACS rating

77. The ratio of a material's flux density to a test coil's magnetizing force,(B/H), can beused to determine the material's:

A. ConductivityB. ResistivityC. Lift-off D. Permeability

78. The magnetic field generated by eddy currents induced in a test specimen: A. Opposes the magnetic field that induced the eddy currentsB. Reinforces the magnetic field that induced the eddy currentsC. Cancels the magnetic field that induced the eddy currentsD. Has no effect on the magnetic field that induced the eddy currents

79. The impedance of a test coil usually can be represented by the vector sum of: A. Inductive reactance and resistanceB. Capacitive reactance and resistanceC. Inductive reactance and capacitive reactanceD. Inductance and capacitance

80. For age hardenable aluminum and titanium alloys, changes in hardness are indicated bychanges in:

A. RententivityB. PermeabilityC. ConductivityD. Magnetostriction

81. The penetration of eddy currents in a conductive material is decreased when:A. Test frequency or conductivity of the specimen is decreasedB. Test frequency is decreased or conductivity of the specimen is increasedC. Test frequency, conductivity of the specimen or permeability of the specimen

are increased D. Permeability of the specimen is decreased

82. When the electrical current in an eddy current coil reverses direction: A. The direction of the eddy currents in a part remains the sameB. The eddy currents in the test part will change phase 45 degrees C. The direction of the eddy currents in the part also reversesD. The eddy currents in the part remain the same

83. When testing magnetic materials in a ac field, increasing the field strength:A. Has no effectB. Increases eddy current penetrationC. Decreases eddy current penetrationD. Decreases eddy current penetration to some minimum value, and

then increases it to its maximum value when the specimen becomes magnetically saturated

84. Impedance diagrams have been mathematically derived and experimentally verified for materialsof any conductivity and permeability having rectangular, cylindrcal, or spherical symmetry. Totest all specimens of similar geometry under the same condition, it is only necessary to choose a test frequency, (f), so that frequency ratio f/f lies at the same point on the impedance diagram for each specimen. This principle is based upon:

A. Ohm's law B. Kirchoff's law C. The Similarity Law D. None of these

85. To be useful, limit frequency equations must be: A. Used with their impedance diagramsB. Used to determine their impedance diagramsC. Both of theseD. Neither of these

86. When a rod is placed in an encircling type of coil, the density of eddy currents will be greatest:

A. At the surface B. At the centerC. Midway between the surface and centerD. None of these

87. term fill factor applies to:A. A surface coilB. Coaxial cableC. A encircling coilD. All of these

88. An eddy current system using handling equipment with automatic marking of the defective areas primarily makes it possible to:

A. Remove defective areas of the product, if desiredB. Eliminate test surface contaminationC. Allow an inexperienced operator to establish the defect causeD. Pass rejectable material

89. 2 TEST COILS ARE OFTEN USED IN A BRIDGE CIRCUIT A. Eliminate skin effect B. Determine the differences between a known standard sampleC. Increase the conductivity of the circuitD. Decreases the system sensitivity

90. In inspecting ferromagnetic materials, relatively low frequencies are normally used becauseof the:

A. Low penetrability of these materialsB. Higher resolutionC. Lower esolutionD. Higher penetrability of these materials

91. The actual frequency used in any specific eddy current inspection should be selectedon the basis of the:

A. Thickness of the material B. Desired depth of penetrationC. Degree of sensitivity or resolution requiredD. Purpose of the inspection E. All of these

92. In modulation analysis testing, which of the following would not modulate the testfrequency applied to the test coil?

A. Discontinuities in the test specimenB. Dimension changes of the test specimenC. Chemical composition of the test specimenD. A filter in the test circuit

electromagnetic testing q&a 002

Documents