Electromagnetic testing q&a 002

Electromagnetic Testing Q&A -001 (without standard answers) My ASNT Level III Pre-Exam Preparatory Self Study Notes 7th May 2015

Charlie Chong/ Fion Zhang

Petrochemical Applications

Charlie Chong/ Fion Zhang

http://independent.academia.edu/CharlieChong1 http://www.yumpu.com/zh/browse/user/charliechong http://issuu.com/charlieccchong

Charlie Chong/ Fion Zhang

Charlie Chong/ Fion Zhang

Fion Zhang at Shanghai 7th May 2015

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

Charlie Chong/ Fion Zhang

REVIEW QUESTIONS without standard answers

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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

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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

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7.

A. B. C. D.

The fill factor when a 1/2 inch diameter bar is inserted in a 1 inch diameter coil is: 0.5 (50%) 0.75 (75%) 1.0 (100%) 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

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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 phase D. Retentivity harmonic frequencies 11. The inductive reactance of a test coil can be calculated using the formula: A. Xr = 2 pie L B. Xr = 1/2 pie L C. Xr = 2 pie fL D. 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

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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

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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

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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 geometry D. 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

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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 frequency C. Neither D. 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 phase B. 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 discontinuity D. 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 conditions produce in the test signal is: A. Phase distortion B. Phase shifting C. Phase discrimination D. Phase analysis

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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)

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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 frequency required to give an f/fq ratio of 10 would be: A. 1.25 Hz B. 12.5 Hz C. 1.25 kHz D. 12.5 kHz 26. At a fixed test frequency, in which of the following materials will the eddy current 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 rotate magnetic domains can be eliminated by: A. Increasing the rate of displacement of the specimen through the coil B. Magnetically saturating the test specimen C. Decreasing the rate of displacement of the test specimen throughthe test coil D. Testing in an air-conditioned room

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28. A term used to define any change in a sinusoidal signal when the output is not a linear reproduction of the input is: A. Distortion B. Linearity C. Phase shifting D. Dynamic range 29. If the test frequency increases while field strength is held constant, the surface density eddy current A. Decreases B. Increases C. Remains the same D. Could do any of the 3 answers 30. As the fill factor decreases, the impedance variation of a pickup coil produced by a given change in conductivity will: A. Increase B. Remain the same C. Decrease D. Could do any of the 3

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

A. Gradual changes in diameter B. Gradual changes in conductivity C. Changes in temperature D. Short flaws 32. The magnetic domains in an unmagnetized ferromagnetic material are: A. Arranged to facilitate the condition of electrons B. Randomly oriented and neutralize each other C. Uniformly oriented D. 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. Induction B. Conduction C. Heat transfer D. Magnetic domain transfer

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34. To eliminate any dependence upon the number of turns of a test coil, the inductance values of an impedance diagram are: A. Disregarded B. Normalized C. 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 total coil impedance regardless of the phase or direction in which it occurs on an impedance plane is: A. Inductive reactance magnitude system B. Feedback-controlled system C. Impedance-magnitude system D. 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 discontinuities B. Conductivity changes C. Diameter changes D. Wall thickness variations Charlie Chong/ Fion Zhang

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 skipping C. 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 which are the smallest known permanent magnets. These regions are called: A. Lattice structures B. Cells C. 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 coil D. Greater than the flux density generated by the test coil

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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 B D. Letter H 42. In eddy current testing, the specimen is coupled to the test coil by: A. Core coupling B. Magnetic saturation C. The coil's magnetic field D. Magnetic domains

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43. The thickness of nonconductive coatings on a conductive base can be most simply measuredby: A. Observing the lift-off effect caused by the coating B. Testing both sides of the specimen C. Varying the current in the test coil D. 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 penetration B. Increase the magnetic field extension and eddy current penetration C. 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 coils B. Test frequency C. Overall shape of the coils D. Distance from other coils

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46. The formula used to calculate the impedance of an eddy current test coil is: A. Z = 2 pie fl B. Z = X,+R C. Z = the square root X,+R D. 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 coil B. 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 coil B. Encircling coil C. Spinning coil D. Gap coil

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49. A term used to define an eddy current test coil which uses magnetic material to purposely shape the magnetic field is: A. Bobbin coil B. Encircling coil C. Spinning coil D. Gap coil ?

50. The vector-point, ellipse, and linear time-base methods are all subdivisions of the: A. Impedance method of testing B. The modulation analysis method of testing C. The phase analysis method of testing D. None of these are correct 51. It is frequently possible to separate the conductivity variable from the permeability and dimensional variables when using: A. The vector-point method of testing B. The ellipse method of testing C. The linear time-base method of testing D. Any of these methods of testing

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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 tube B. An ellipse method of testing C. A null reading on a meter D. 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 ellipse B. Horizontal length of the straight line C. Size of the ellipse opening D. Sinusoidal shape of the waveform 54. When eddy current testing by the linear time base method, what is applied to the vertical deflection plates of a cathod ray tube when the test specimen and reference standard 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 voltage C. A sawtooth waveform D. Zero net voltage Charlie Chong/ Fion Zhang

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

A. A sinusoidal wave B. A sawtooth wave C. A squarewave D. No voltage 56. The conductivity value for a metal is a function of the : A. Heat treatment given the metal B. Cold working performed on the metal C. Aging process used on the metal D. 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 2 B. Greater than 2 C. Greater than 4 D. Greater than 10

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

A. Aluminum B. Fiberglass C. Copper D. Steel 59. A term used to define a surface or internal rupture which is attributed to processing at low a temperature or excessive working or metal movement during the forging, rolling, or extruding operation is: A. Cold shut B. Micro shrinkage C. Burst D. Inclusion 60. A term used to define the timing relationship invovled in alternating current signals is: A. Magnitude B. Phase C. Impedance D. Reactance

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61. When eddy current testing a nonferrous material, the choice of test frequency is determinedby the : A. Degree of phase discrimination required B. Eddy current penetration needed C. 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 flux B. Leakage flux C. Induced flux D. None of these 63. A term to define a property of a test system which enables the separation of signals due to discontinuities in the test specimen that are located in close proximity to each other is: A. Dynamic range B. Sensitivity C. Linearity D. Discontinuity resolution Charlie Chong/ Fion Zhang

64. A term used to define a material having a permeability less than that of a vacum is A. Magnetic B. Diamagnetic C. Ferromagnetic D. Paramagnetic 65. The inductive reactance of a coil is measured in units of: A. Mhos B. 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 differential B. Self-comparison differential C. Single coil absolute D. Double coil absolute

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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 tested B. The specimen should have the same heat treatment as the piece to be tested C. The surface finish of the specimen should be the same as the piece to be tested D. 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 variables of no interest on the readout mechanism are based on differences in: A. Amplitude B. Phase C. Frequency D. Any one or a combination of the quantities listed above

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70. When a nonmagnetic rod is placed inside an eddy current test coil: A. The magnetic field generated by the coil is increased in intensity B. The distribution of eddy currents is uniform through the rod's cross section C. 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 permeability B. An increase in resistivity C. A decrease in permeability D. A decrease in resistivity

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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. Increases B. Remains the same C. Decreases D. May increase or decrease 74. When the voltage applied to a circuit and the current through the circuit both reach their maximums and minimums at the same time, the voltage and current are: A. Additive B. In phase C. Regenerative D. Out of phase 75. Which of the following is not a commonly used eddy current testing readout mechanism?

A. Signal generator B. Meter C. Cathode ray tube D. Strip-chart recorder

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76. Which of the following materials would have the highest resistivity value?

A. Aluminum with a 42% IACS rating B. Magnesium with a 37% IACS rating C. Cast steel with a 10.7% IACS rating D. 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. Conductivity B. Resistivity C. 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 currents B. Reinforces the magnetic field that induced the eddy currents C. Cancels the magnetic field that induced the eddy currents D. Has no effect on the magnetic field that induced the eddy currents

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79. The impedance of a test coil usually can be represented by the vector sum of: A. Inductive reactance and resistance B. Capacitive reactance and resistance C. Inductive reactance and capacitive reactance D. Inductance and capacitance 80. For age hardenable aluminum and titanium alloys, changes in hardness are indicated bychanges in: A. Rententivity B. Permeability C. 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 decreased B. Test frequency is decreased or conductivity of the specimen is increased C. Test frequency, conductivity of the specimen or permeability of the specimen are increased D. Permeability of the specimen is decreased

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82. When the electrical current in an eddy current coil reverses direction: A. The direction of the eddy currents in a part remains the same B. The eddy currents in the test part will change phase 45 degrees C. The direction of the eddy currents in the part also reverses D. 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 effect B. Increases eddy current penetration C. Decreases eddy current penetration D. 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. To test 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

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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 equivalently The algebraic sum of currents in a network of conductors meeting at a point is zero.

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

Short research about the history of eddy current The 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 LĂŠon 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.

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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 diagrams B. Used to determine their impedance diagrams C. Both of these D. 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 center C. Midway between the surface and center D. None of these 87. term fill factor applies to: A. A surface coil B. Coaxial cable C. A encircling coil D. All of these

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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 desired B. Eliminate test surface contamination C. Allow an inexperienced operator to establish the defect cause D. 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 sample C. Increase the conductivity of the circuit D. Decreases the system sensitivity 90. In inspecting ferromagnetic materials, relatively low frequencies are normally used becauseof the: A. Low penetrability of these materials B. Higher resolution C. Lower resolution D. Higher penetrability of these materials

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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 penetration C. Degree of sensitivity or resolution required D. Purpose of the inspection E. All of these 92. In modulation analysis testing, which of the following would not modulate the test frequency applied to the test coil?

A. Discontinuities in the test specimen B. Dimension changes of the test specimen C. Chemical composition of the test specimen D. A filter in the test circuit

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Good Luck

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

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Further Reading

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Good Luck

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

1. A method of minimizing the effect of indications caused by gradual dimensional changes whileretaining the indications caused by discontinuities is to: Include a high pass filter in the eddy current test equipment A. Include a low pass filter in the eddy current test equipment B. Increase the band pass of the amplifier C. Use the impedance method of testing D. 2. Which of the following methods may be used to improve the signal-to-noise ratio of an eddycurrent test system?

Filtering or differentiation A. Phase discrimination B. Intergration C. All 3 are correct D. 3. In order to decrease the effect on conductivity readings due to variations in test part thickness: The test frequency should be increased A. The test frequency should be decreased B. The fill factor should be decreased C. There is no practical method for decreasing this effect D. 4. When testing by the eddy current method, discontinuities will be most easily detected when the eddy currents are: Coplanar with the major plane of the discontinuity A. Perpendicular to the major plane of the discontinuity B. Parallel to the major plane of the discontinuity C. 90 degress out of the phase with current in the coil D. 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: Fill factor A. Edge effect B. End effect C. Lift off D. 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: Skin effect A. High frequency filtration B. Low frequency filtration C. Any of these answers D. 7. The fill factor when a 1/2 inch diameter bar is inserted in a 1 inch diameter coil is: 0.5 (50%) A. 0.75 (75%) B. 1.0 (100%) C. 0.25 (25%) D.

8. The term used to define the difference between actual instrument output and expectedoutput as defined by a straight line calibration curve is: Phase shift A. Nonlinearity B. Lift off C. Skin effect D. 9. Which of the following could be used to suppress unwanted high frequency harmonics?

Low pass filter A. Oscillator B. Phase discriminator C. High pass filter D. 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: Capacitive reactance and resistance A. Harmonic frequencies and inductive reactance B. Signal ampllitude and phase C. Retentivity harmonic frequencies D. 11. The inductive reactance of a test coil can be calculated using the formula: Xr = 2 pie L A. Xr = 1/2 pie L B. Xr = 2 pie fL C. Xr = 1R D. 12. When conducting an eddy current test, variations in the test material can be detectedas variations in: Test speed A. Impedance of the pickup coil B. None of the 2 answers C. Both answers are correct D. 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: Differential A. Absolute B. Laminar C. Flying probes D. 14. Tubing is generally inspected using: U-Shaped coils A. Gap coils B. Encircling coils C. None of the answers D.

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

Length of the test sample A. Thickness of the test sample B. Cross-sectional area of the test sample C. All answers are correct D. 16. In a test coil consisting of both a primary and secondary winding, the voltage across thesecondary is a function of: Test material permeability A. Test frequency B. Geometry of the test object C. All answers are correct D. 17. Eddy current testing relies on the principle of: Magnetostriction A. Electromagnetic induction B. Piezoelectric energy conversion C. Magnetomotive force D. 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: Coercive force A. Residual Magnetism B. Saturation value C. Hysteresis loss D. 19. The term used to define the value of H field required to decrease the remanence of a material to zero is: Coercive force A. Magnetizing force B. Back emf C. The overlap value D. 20. The 3 major specimen parameters which influence eddy current testing are: Electrical conductivity, frequency, and material geometry A. Density, permeability, and frequency B. Electrical conductivity, permeability, and material geometry C. Thermal conductivity, electrical conductivity, and permeability D. 21. Doubling the number of turns on a coil will: Double the inductance A. Halve the inductance B. Decrease the inductance by a factor of 4 C. Increase the inductance by a factor of 4 D. 22. Frequency ratio f/f can be defined as: The argument of the mathematical function describing the electromagnetic field A. within the test specimen Test frequency divided by limit frequency B. Neither C. Both D.

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

The signals are in phase A. The phase of the OD discontinuity leads the phase of the ID discontinuity B. The phase of the OD discontinuity lags the phase of the ID discontinuity C. Indeterminate D. 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: Phase distortion A. Phase shifting B. Phase discrimination C. Phase analysis D. 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: 1.25 Hz A. 12.5 Hz B. 1.25 kHz C. 12.5 kHz D. 26. At a fixed test frequency, in which of the following materials will the eddy currentpenetration be greatest?

Aluminum (35% IACS conductivity) A. Brass (15% IACS conductivity) B. Copper (95% IACS conductivity) C. Lead (7% IACS conductivity) D. 27. The heating effect in magnetic materials caused by work required to rotate magneticdomains can be eliminated by: Increasing the rate of displacement of the specimen through the coil A. Magnetically saturating the test specimen B. Decreasing the rate of displacement of the test specimen throughthe test coil C. Testing in an air-conditioned room D. 28. A term used to define any change in a sinusoidal signal when the output is not a linearreproduction of the input is: Distortion A. Linearity B. Phase shifting C. Dynamic range D. 29. If the test frequency increases while field strength is held constant, the surface density:eddy current Decreases A. Increases B. Remains the same C. Could do any of the 3 answers D.

30. As the fill factor decreases, the impedance variation of a pickup coil producedby a given chaange in conductivity will: Increase A. Remain the same B. Decrease C. Could do any of the 3 D. 31. Which of the following would be easier to detect in tubing by the eddy currentmethod using self comparison differential coil arrangement?

Gradual changes in diameter A. Gradual changes in conductivity B. Changes in temperature C. Short flaws D. 32. The magnetic domains in an unmagnetized ferromagnetic material are: Arranged to facilitate the condition of electrons A. Randomly oriented and neutralize each other B. Uniformly oriented C. Create a major north and south pole in the material D. 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: Induction A. Conduction B. Heat transfer C. Magnetic domain transfer D. 34. To eliminate any dependence upon the number of turns of a test coil, the inductancevalues of an impedance diagram are: Disregarded A. Normalized B. Corrected to a value of 1 C. None of the 3 answers D. 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: Inductive reactance magnitude system A. Feedback-controlled system B. Impedance-magnitude system C. Impedance vector analysis system D. 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?

Small discontinuities A. Conductivity changes B. Diameter changes C. Wall thickness variations D.

37. A major problem associated with eddy current test method is the: Inability of eddy current testing to accurately measure conductivity A. Need to test at low speeds to prevent skipping B. Large number of known or unknown variables which appear in the C. output indication Inability of eddy current testing to detect small discontinuities D. 38. The atoms of a metal showing magnetic characteristics are grouped into regions whichare the smallest known permanent magnets. These regions are called: Lattice structures A. Cells B. Domains C. Planetary spins D. 39. When a coil's magnetizing force is applied to a ferromagnetic material, the flux densityin the material is: Less than the flux density generated by the test coil because of heat A. losses Less than the flux density generated by the test coil because of resistivity B. The same as the flux density generated by the test coil C. Greater than the flux density generated by the test coil D. 40. The flux density in a magnetic material is usually designated by the : Symbol u A. Symbol o B. Letter B C. Letter H D. 41. The magnetizing force of an eddy current test coil is usually designated by the: Symbol u A. Symbol o B. Letter--B C. Letter--H D. 42. In eddy current testing, the specimen is coupled to the test coil by: Core coupling A. Magnetic saturation B. The coil's magnetic field C. Magnetic domains D. 43. The thickness of nonconductive coatings on a conductive base can be most simply measuredby: Observing the lift-off effect caused by the coating A. Testing both sides of the specimen B. Varying the current in the test coil C. Varying the test frequency over a given range during the test D. 44. The use of magnetic shielding around the exciting coil will generally: Increase the magnetic field extension but decrease the eddy current penetration A. Increase the magnetic field extension and eddy current penetration B. Decrease the magnetic field extension but increase the eddy current C. penetration Decrease the magnetic field extension and eddy current penetration D.

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

Diameter of coils A. Test frequency B. Overall shape of the coils C. Distance from other coils D. 46. The formula used to calculate the impedance of an eddy current test coil is: Z = 2 pie fl A. Z = X,+R B. Z = the square root X,+R C. Z = the square root X, to the 2nd power+R to the 2nd power D. 47. An out-of-phase condition between current and voltage: Can exist only in the primary winding of an eddy current coil A. Can exist only in the secondary winding of an eddy current coil B. Can exist in both the primary and secondary windings of an eddy current coil C. Exist only in the test specimen D. 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: Bobbin coil A. Encircling coil B. Spinning coil C. Gap coil D. 49. A term used to define an eddy current test coil which uses magnetic material to purposelyshape the magnetic field is: Bobbin coil A. Encircling coil B. Spinning coil C. Gap coil D. 50. The vector-point, ellipse, and linear time-base methods are all subdivisions of the: Impedance method of testing A. The modulation analysis method of testing B. The phase analysis method of testing C. None of these are correct D. 51. It is frequently possible to separate the conductivity variable from the permeability anddimensional variables when using: The vector-point method of testing A. The ellipse method of testing B. The linear time-base method of testing C. Any of these methods of testing D. 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 straight horizontal line on the cathode tube A. An ellipse method of testing B. A null reading on a meter C. A clean base line on a strip chart D.

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: Brightness of the ellipse A. Horizontal length of the straight line B. Size of the ellipse opening C. Sinusoidal shape of the waveform D. 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 sinusoidal wave in phase with the timing voltage A. A sinussoidal wave 90 degrees out of phase with the timing voltage B. A sawtooth waveform C. Zero net voltage D. 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 sinusoidal wave A. A sawtooth wave B. A squarewave C. No voltage D. 56. The conductivity value for a metal is a function of the : Heat treatment given the metal A. Cold working performed on the metal B. Aging process used on the metal C. All of the answers D. 57. The ratio of the specific diameter of a probe to the minimum discontinuity of interest should be: Less than 2 A. Greater than 2 B. Greater than 4 C. Greater than 10 D. 58. Which of the following materials would be more likely used as a mounting material for a probecoil?

Aluminum A. Fiberglass B. Copper C. Steel D. 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: Cold shut A. Micro shrinkage B. Burst C. Inclusion D.

60. A term used to define the timing relationship invovled in alternating current signals is: Magnitude A. Phase B. Impedance C. Reactance D. 61. When eddy current testing a nonferrous material, the choice of test frequency is determinedby the : Degree of phase discrimination required A. Eddy current penetration needed B. Rate of response required C. All of these D. 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: Air flux A. Leakage flux B. Induced flux C. None of these D. 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: Dynamic range A. Sensitivity B. Linearity C. Discontinuity resolution D. 64. A term used to define a material having a permeability less than that of a vacum is Magnetic A. Diamagnetic B. Ferromagnetic C. Paramagnetic D. 65. The inductive reactance of a coil is measured in units of: Mhos A. Ohms B. Henry's C. Gauss D. 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?

External reference differential A. Self-comparison differential B. Single coil absolute C. Double coil absolute D.

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

The specimen should be of the same size and shape as the piece A. to be tested The specimen should have the same heat treatment as the piece to be tested B. The surface finish of the specimen should be the same as the piece to be tested C. If the material is aluminum, the surface should be anodized D. 68. An eddy current test coil's magnetic field intensity in air: Increases with distance outside the coil and varies across the diameter inside the A. coil Decreases with distance outside the coil and varies across the diameter inside B. the coil Decreases with distance outside the coil and is assumed to be constant across C. the diameter inside the coil Increases with distance outside the coil and is assumed to be D. 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: Amplitude A. Phase B. Frequency C. Any one or a combination of the quantities listed above D. 70. When a nonmagnetic rod is placed inside an eddy current test coil: The magnetic field generated by the coil is increased in intensity A. The distribution of eddy currents is uniform through the rod's cross section B. The distribution of eddy currents is at a maximum at the rod's surface, or near C. the surface,and decreases to essentially zero at the rod's center The temperature of the rod decreases D. 71. The symbol commonly used to signify impedance is: Z A. X; E B. R C. Xc D. 72. A decrease in conductivity is equivalent to: An increase in permeability A. An increase in resistivity B. A decrease in permeability C. A decrease in resistivity D. 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: Increases A. Remains the same B. Decreases C. May increase or decrease D.

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: Additive A. In phase B. Regenerative C. Out of phase D. 75. Which of the following is not a commonly used eddy current testing readout mechanism?

Signal generator A. Meter B. Cathode ray tube C. Strip-chart recorder D. 76. Which of the following materials would have the highest resistivity value?

Aluminum with a 42% IACS rating A. Magnesium with a 37% IACS rating B. Cast steel with a 10.7% IACS rating C. Zirconium with a 3.4% IACS rating D. 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: Conductivity A. Resistivity B. Lift-off C. Permeability D. 78. The magnetic field generated by eddy currents induced in a test specimen: Opposes the magnetic field that induced the eddy currents A. Reinforces the magnetic field that induced the eddy currents B. Cancels the magnetic field that induced the eddy currents C. Has no effect on the magnetic field that induced the eddy currents D. 79. The impedance of a test coil usually can be represented by the vector sum of: Inductive reactance and resistance A. Capacitive reactance and resistance B. Inductive reactance and capacitive reactance C. Inductance and capacitance D. 80. For age hardenable aluminum and titanium alloys, changes in hardness are indicated bychanges in: Rententivity A. Permeability B. Conductivity C. Magnetostriction D. 81. The penetration of eddy currents in a conductive material is decreased when: Test frequency or conductivity of the specimen is decreased A. Test frequency is decreased or conductivity of the specimen is increased B. Test frequency, conductivity of the specimen or permeability of the specimen C. are increased Permeability of the specimen is decreased D.

82. When the electrical current in an eddy current coil reverses direction: The direction of the eddy currents in a part remains the same A. The eddy currents in the test part will change phase 45 degrees B. The direction of the eddy currents in the part also reverses C. The eddy currents in the part remain the same D. 83. When testing magnetic materials in a ac field, increasing the field strength: Has no effect A. Increases eddy current penetration B. Decreases eddy current penetration C. Decreases eddy current penetration to some minimum value, and D. 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: Ohm's law A. Kirchoff's law B. The Similarity Law C. None of these D. 85. To be useful, limit frequency equations must be: Used with their impedance diagrams A. Used to determine their impedance diagrams B. Both of these C. Neither of these D. 86. When a rod is placed in an encircling type of coil, the density of eddy currents will be greatest: At the surface A. At the center B. Midway between the surface and center C. None of these D. 87. term fill factor applies to: A surface coil A. Coaxial cable B. A encircling coil C. All of these D. 88. An eddy current system using handling equipment with automatic marking of the defective areas primarily makes it possible to: Remove defective areas of the product, if desired A. Eliminate test surface contamination B. Allow an inexperienced operator to establish the defect cause C. Pass rejectable material D.

89. 2 TEST COILS ARE OFTEN USED IN A BRIDGE CIRCUIT Eliminate skin effect A. Determine the differences between a known standard sample B. Increase the conductivity of the circuit C. Decreases the system sensitivity D. 90. In inspecting ferromagnetic materials, relatively low frequencies are normally used becauseof the: Low penetrability of these materials A. Higher resolution B. Lower esolution C. Higher penetrability of these materials D. 91. The actual frequency used in any specific eddy current inspection should be selectedon the basis of the: Thickness of the material A. Desired depth of penetration B. Degree of sensitivity or resolution required C. Purpose of the inspection D. All of these E. 92. In modulation analysis testing, which of the following would not modulate the testfrequency applied to the test coil?

Discontinuities in the test specimen A. Dimension changes of the test specimen B. Chemical composition of the test specimen C. A filter in the test circuit D.