Eddy Current Level I Flashcards by Michael Shigley

1) In electromagnetic testing, which of the following is not a source of noise?

a. Geometrical changes
b. Permeability variations within the test object
c. Electrical interference
d. Coil size

d. Coil size

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2) The ratio of the response or amplitude from signals of interest to the response or amplitude of indications that contain no useful information for the test being conducted is referred to as:

a. aspect ratio
b. signal-to-noise ratio
c. the conductivity-to-permeability ratio
d. the reactance-to-resistance ratio

b. signal-to-noise ratio

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3) Which of the following is not a basic component of an eddy current test system?

a. Amplifier
b. Sine wave generator
c. Wear-resistant tape
d. Filter

c. Wear-resistant tape

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4) When conducting an eddy current test using a differential comparison coil arrangement that compares an external reference standard with the test specimen, the system should be nulled or balanced:

a. with only the reference standard in one coil
b. with the reference standard in one coil and an acceptable test specimen in the other coil
c. with the reference standard in one coil and an unacceptable test specimen in the other coil
d. with only the test specimen in one coil

b. with the reference standard in one coil and an acceptable test specimen in the other coil

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5) The impedance of a test coil will increase if the:

a. test frequency increases
b. inductive reactance of the coil decreases
c. inductance of the coil decreases
d. resistance of the coil decreases

a. test frequency increases

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6) Some of the products commonly tested using encircling coils are:

a. rods, tubes, and wire
b. plate when volumetrically inspected
c. sheets and metalized foil
d. structural steel welds

a. rods, tubes, and wire

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7) Which of the following would normally be considered the best fill factor when testing straight tubing with an encircling or feedthrough coil?

a. 1.75 (175%)
b. 0.95 (95%)
c. 0.50 (50%)
d. 0.25 (25%)

b. 0.95 (95%)

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8) When a metal part is placed in an eddy current test coil, the impedance of the coil will be changed by all of the following properties of the part except:

a. conductivity
b. dimensions
c. permeability
d. nonconductive coating

d. nonconductive coating

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9) An eddy current test makes use of electrical current induced in a conductive article by:

a. gamma rays
b. an alternating magnetic field
c. a piezoelectric force
d. a decay process

b. an alternating magnetic field

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10) The conductivity of a material can be altered by changing the:

a. amount of paint on the part surface
b. chemistry of the part
c. length of the part
d. volume of the part

b. chemistry of the part

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11) The depth to which eddy currents are induced in the material is determined mostly by the:

a. thickness of the material
b. diameter of the material
c. geometrical shape of the material
d. test frequency

d. test frequency

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12) When testing plate with a probe coil, it is noted that the eddy current output indication varies as the distance from the coil to the surface of the test part varies. The term used to describe this action is:

a. fill factor
b. liftoff
c. phase differentiation
d. edge effect

b. liftoff

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13) The main purpose for spring-loaded eddy current probe coils is to:

a. minimize liftoff variations
b. minimize wear on the probe
c. reduce operator fatigue
d. eliminate edge effect

a. minimize liftoff variations

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14) Liftoff is utilized in:

a. measuring permeability changes
b. measuring conductivity changes
c. measuring the thickness of nonconductive coatings
d. determining proper test frequency

c. measuring the thickness of nonconductive coatings

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15) In eddy current test systems where encircling coils are used, coupling efficiency is referred to as:

a. liftoff
b. edge effect
c. fill factor
d. phase differentiation

c. fill factor

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16) When inspecting products with a uniform cross section, an eddy current signal is produced when the leading end or trailing end of the product approaches the test coil. This phenomenon is referred to as:

a. liftoff
b. end effect
c. fill factor
d. phase discrimination

b. end effect

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17) Which of the following conditions would be the most difficult to detect when eddy current testing a rod with an encircling coil?

a. A deep surface crack that has a depth of 30% of the rod diameter
b. A small inclusion in the center of the rod
c. A 5% change in diameter
d. A 10% change in conductivity

b. A small inclusion in the center of the rod

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18) When testing tubing with a bobbin coil, most of the eddy currents:

a. flow in a longitudinal direction down the tubing
b. flow radially in the tube
c. flow around only the outside diameter of the tubing
d. flow around the inside diameter of the tubing

d. flow around the inside diameter of the tubing

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19) Which of the following test frequencies would produce eddy currents with the largest depth of penetration?

a. 100 Hz
b. 10 kHz
c. 1 MHz
d. 10 MHz

a. 100 Hz

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20) A test coil’s opposition to the flow of alternating current, causing the current to lag behind the voltage, is called:

a. resistance
b. inductive reactance
c. impedance
d. capacitive reactance

b. inductive reactance

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21) An increase in the impedance of a test coil will:

a. produce an increase in the voltage through the test coil
b. cause a decrease in the measured voltage across the test coil
c. not affect the voltage in the test coil
d. decrease the voltage applied to the coil

a. produce an increase in the voltage through the test coil

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22) Which of the following will not affect the inductance of a test probe?

a. Test frequency
b. Number of turns of wire in the coil
c. Coil width
d. Coil cross-sectional area

a. Test frequency

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23) When a test coil consists of a double winding arrangement and one winding is referred to as a primary winding, the other winding is referred to as the:

a. absolute winding
b. secondary winding
c. phase winding
d. differential winding

b. secondary winding

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24) Large-diameter surface scanning coils would most likely be used for the detection of:

a. pitting
b. small inclusions
c. changes in conductivity
d. porosity

c. changes in conductivity

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25) Small-diameter probe coils would typically be used for the detection of: a. slow changes in dimensions b. gradual changes in conductivity c. variation in heat treatment d. small surface discontinuity

d. small surface discontinuity

26) Direct current saturation coils would most likely be used when testing: a. carbon steel b. aluminum c. copper d. brass

a. carbon steel

27) An absolute coil arrangement can be used in: a. encircling coils only b. probe coils only c. probe and encircling coils only d. probe, encircling, and inside diameter coils

d. probe, encircling, and inside diameter coils

28) Which of the following expresses the primary purposes of the secondary windings in an eddy current probe? a. Induce eddy currents in the test specimen b. Detect changes in the eddy current flow c. Induce eddy currents in the test specimen and detect changes in the eddy current flow d. Provide DC saturation

b. Detect changes in the eddy current flow

Which of the following eddy current test coil arrangements uses one area of the test specimen as a reference standard against which another area on the same specimen is simultaneously compared? a. Single absolute coil b. Double absolute coil c. DC saturation coil d. Differential coil

d. Differential coil

30) Reference standards used for electromagnetic testing: a. must contain artificial discontinuities such as notches and drilled holes b. must contain natural discontinuities such as cracks and inclusions c. must be free of measurable discontinuities d. may contain artificial or natural discontinuities or be free of discontinuities depending on the test system and the type of test being conducted

d. may contain artificial or natural discontinuities or be free of discontinuities depending on the test system and the type of test being conducted

31) A tool used to ensure that the test system does not drift during a test cycle is called a: a. DGS standard b. calibration standard c. mix algorithm d. probe

b. calibration standard

32) Which of the following could not be tested by the electromagnetic testing method? a. A 102 mm (4 in.) thick plate to be tested for small discontinuities throughout the plate b. Tubing to be tested for surface cracks c. Rod to be tested for laps and seams d. Tubing to be tested for variations in outside diameter

a. A 102 mm (4 in.) thick plate to be tested for small discontinuities throughout the plate

33) Which of the following is not true about an eddy current test? a. It can be used for high-speed testing b. It can accurately measure conductivity c. It can be set up to provide high sensitivity to small discontinuities d. It can penetrate up to 152 mm (6 in.) in a test part

d. It can penetrate up to 152 mm (6 in.) in a test part

34) The entire circumference of a tube can be evaluated at one time when using: a. an encircling coil b. a bobbin coil c. a pencil probe d. a pancake coil

a. an encircling coil

35) When attempting to determine the exact circumferential location of a discontinuity in a tube, the test system should include: a. a phase shifter b. a probe coil c. an attenuator d. a penetrameter

b. a probe coil

36) It is often possible to sort various nonferromagnetic alloys of a metal by means of an eddy current test when: a. there is a unique range of permeability values for each alloy b. there is a unique range of conductivity values for each alloy c. the direction of induced eddy currents varies for each alloy d. the magnetic domains for each alloy are different

b. there is a unique range of conductivity values for each alloy

37) Which of the following products would be most applicable to a test using an inside coil? a. Sheet b. Rod c. Bolt hole d. Coating thickness

c. Bolt hole

38) When eddy current testing a rod for discontinuities, which of the following would not be considered a source of noise? a. Improper adjustment of the hold-down rollers used to center the rod in the coil b. Feeding rod through the coil at an excessive speed c. Pits d. Tube end responses

c. Pits

39) One method of reducing nonrelevant indications when eddy current testing ferromagnetic materials is to: a. decrease the pressure on the hold-down rollers b. use a direct current saturation coil to magnetically saturate the test specimen c. readjust the gain control d. increase the rate of feedthrough in the coil

b. use a direct current saturation coil to magnetically saturate the test specimen

40) In order to generate measurable eddy currents in a test specimen, the specimen must be: a. a conductor b. an insulator c. either a conductor or an insulator d. a ferromagnetic material

a. a conductor

41) When using an encircling coil with both primary and secondary windings, the excitation current is applied to: a. the secondary winding b. the primary winding c. either the primary or secondary winding depending on the setting of an instrument control d. both the primary and secondary coils

b. the primary winding

42) Which of the following is not a readout system used to present eddy current test information? a. Alarms b. Litmus paper c. Cathode ray tube d. Digital data storage

b. Litmus paper

43) Which of the following statements best describes the selection of eddy current test frequency? a. The frequency must equal the f/fc ratio to give an accurate test b. The frequency must be within ±3% of the f/fc ratio to give an accurate test c. There is a range of suitable frequencies centered around the optimum frequency d. The frequency should be within ±25% of the characteristic frequency

c. There is a range of suitable frequencies centered around the optimum frequency

44) Which of the following options would not have the potential to improve the displayed signal-to-noise ratio of a test? a. Change to a test frequency that will decrease the noise b. Increase the amplification of the test instrument c. Improve the fill factor d. Enable filter functions in the instrument

b. Increase the amplification of the test instrument

45) When conducting an eddy current test on tubing, the magnitude of the indication caused by a discontinuity is not dependent on the: a. depth of the discontinuity b. width of the discontinuity c. length of the discontinuity d. phase rotation setting adjustments

d. phase rotation setting adjustments

46) A coil's magnetic field may be viewed as a distribution of lines of flux around the coil. The number of lines per unit area is defined as: a. magnetic probability b. flux density c. magnetic coupling d. hysteresis density

b. flux density

47) Eddy current test techniques are best suited to: a. measure nonconductive coating thicknesses on conductive materials b. define the crystalline structure of a material c. define the chemistry of an alloy d. test for delaminations in carbon fiber structures

a. measure nonconductive coating thicknesses on conductive materials

48) Eddy currents cannot be induced in: a. latex paint b. aluminum c. steel d. copper

a. latex paint

49) Which of the following statements is not true of ferromagnetic materials? a. They have permeability values much greater than 1 b. They do not exhibit any magnetic hysteresis characteristics c. They will have a definite saturation point on a B/H curve d. They will exhibit some degree of residual magnetism

b. They do not exhibit any magnetic hysteresis characteristics

50) Eddy currents always travel: a. in circular paths b. in nonconductive materials c. radially when testing rod with an encircling coil d. in a gas

a. in circular paths

51) For online eddy current inspections in a tubing mill, the effective DC saturation point of ferromagnetic materials is reached when the current applied to the saturation coil is set at a value where for any further increase in that current, the eddy current signal-to-noise ratio will: a. start to increase b. start to decrease c. show no significant change d. suddenly drop to zero

c. show no significant change

52) The depth of penetration would _____ if the localized permeability of a material increased. a. increase b. decrease c. remain constant d. increase the conductivity

b. decrease

53) A term used to define a standardized condition in a device or system which results in zero output is: a. high-frequency standardization b. integration c. null or balance d. differentiation

c. null or balance

54) A term used to describe holes, grooves, notches, etc., that are introduced into a reference standard to provide accurately reproducible quality levels is: a. a natural discontinuity b. an artificial discontinuity c. an ellipse d. damage mechanism identifiers

b. an artificial discontinuity

55) A term used to define one or more turns or loops of a conductor wound in such a manner as to produce an axial magnetic field when current passes through the conductor is: a. a coil b. a resistor c. a capacitor d. an oscillator

a. a coil

56) An eddy current coil arrangement that does not make a comparison with either two sections of the test specimen or one section of the test part and a reference standard is called: a. an absolute coil arrangement b. a self-comparison differential coil arrangement c. an external reference differential coil arrangement d. a dual coil (split core) bolt hole probe

a. an absolute coil arrangement

57) Which of the following is not a common application for eddy current testing? a. measurement of conductivity b. measurement of the thickness of thin metal sections c. detection of surface and subsurface discontinuities d. detection of lack of bonding between conductive and nonconductive material

d. detection of lack of bonding between conductive and nonconductive material

58) Which of the following is not a primary purpose for using an eddy current standard? a. To determine if the eddy current test system is capable of performing the test properly b. To determine if a discontinuity is a cause for rejection c. To determine the instrument control settings needed to pass the highest percentage of test specimens run d. To determine if the sensitivity of a test system has drifted with time

c. To determine the instrument control settings needed to pass the highest percentage of test specimens run

59) Material must be reasonably centered in an encircling test coil of a discontinuity detection system because, even with an acceptable fill factor ratio: a. the coil would otherwise be out of balance b. parts of the material farthest away from the coil, radially, may receive a less sensitive inspection c. the flow of eddy currents around the product will be disturbed, resulting in improper penetration d. lack of proper centering may change the phase adjustment of the instrument

b. parts of the material farthest away from the coil, radially, may receive a less sensitive inspection

60) When you determine that a discontinuity detection instrument has been set up incorrectly, or is defective, all material: a. should be retested since the time that a correct setup or proper operation was last verified b. accepted should be retested c. rejected should be retested d. inspected should be scrapped

a. should be retested since the time that a correct setup or proper operation was last verified

61) An eddy current system will effectively measure variations in conductivity caused by: a. size of the material b. geometric shape of the material c. the process used to cast or form the material d. hardness of the material as a result of heat treatment

d. hardness of the material as a result of heat treatment

62) A length of tubing containing a notch of uniform width and depth running from end to end, when tested with an encircling self-reference differential coil system, will produce: a. erratic signals b. a discontinuous signal c. no signal change d. excessive signals

c. no signal change

63) An encircling coil is generally used to inspect a test object for: a. discontinuities with a circumferential orientation b. deep subsurface discontinuities c. discontinuities on the inside surface d. discontinuities on the outside surface

d. discontinuities on the outside surface

64) One principle advantage of spinning-probe eddy current testing is: a. the ability to locate the exact position of discontinuities b. its relative insensitivity to permeability variations c. increased production rates d. decreased sensitivity to edge effect or end effect

a. the ability to locate the exact position of discontinuities

65) At any given instant, the coil on a spinning-probe eddy current instrument should be inspecting: a. one complete circumference of the product b. an area defined by the size of the probe coil c. one longitudinal line the length of the product d. the complete thickness of the sample

b. an area defined by the size of the probe coil

66) A spinning probe eddy current instrument would be most useful in: a. measuring the hardness of ferromagnetic steel products b. discontinuity detection in hexagonal material c. detecting and precisely locating surface discontinuities d. inspection of copper bus bars for electrical conductivity

c. detecting and precisely locating surface discontinuities

67) In a feedthrough encircling-coil eddy current system, a calibration standard may be used to: a. ensure repeatability and reliability of the setup b. determine the circumferential extent of a discontinuity c. reduce sensitivity to vibration d. measure the test frequency

a. ensure repeatability and reliability of the setup

68) What causes phase shift in an eddy current test coil? a. A change in the ratio of inductive reactance (Xi) to resistance (R) b. A change in the sensitivity setting of the instrument c. Use of modulation analysis d. A change in the display scaling factors

a. A change in the ratio of inductive reactance (Xi) to resistance (R)

69) In a feedthrough encircling coil discontinuity detection eddy current system, what would be the purpose of running a calibration block several times but in various positions (such as top, bottom, left, and right)? a. To check the phase selectivity b. To ensure proper centering of the material in the test coil c. To select the modulation analysis setting d. To select the proper operating speed

b. To ensure proper centering of the material in the test coil

70) In a feedthrough encircling coil eddy current system, DC saturation would probably be most helpful in testing: a. copper water tubing b. titanium tubing c. ferromagnetic steel tubing d. brass rivet wire

c. ferromagnetic steel tubing

71) In an electromagnetic test system, the test frequency is controlled by the: a. oscilloscope b. sensitivity setting c. oscillator circuit d. modulation analysis setting

c. oscillator circuit

72) Variations in the chemical composition of a nonferromagnetic alloy would most likely affect its: a. permeability b. conductivity c. diameter d. frequency

b. conductivity

73) Which of the following frequencies will provide the greatest eddy current penetration in aluminum? a. 1 kHz b. 10 kHz c. 3 kHz d. 300 Hz

d. 300 Hz

74) A symbol commonly used to express conductivity is: a. μ b. σ c. XL d. R

b. σ

75) A symbol commonly used to express permeability is: a. μ b. σ c. XL d. R

a. μ

76) The method used to generate eddy currents in a test specimen by means of a coil can most closely be compared with the action of a: a. transformer b. capacitor c. storage battery d. generator

a. transformer

77) When eddy current is used to test a nonferrous specimen, a discontinuity will: a. increase the effective conductivity of the specimen b. increase the effective permeability of the specimen c. decrease the effective conductivity of the specimen d. cause a decrease in measured voltage across the coil

c. decrease the effective conductivity of the specimen

78) In multifrequency tubing inspection applications, signal analysis is most often performed using: a. phase angle analysis only b. signal amplitude analysis only c. both amplitude and phase information d. the ellipse method

c. both amplitude and phase information

79) When testing tubes with an ID bobbin probe: a. low-voltage signals indicate insignificant discontinuity depths b. high-voltage signals are always from rejectable discontinuities c. signals from support plates always hide discontinuity signals d. the responses from ID discontinuities will lead the responses from OD discontinuities

d. the responses from ID discontinuities will lead the responses from OD discontinuities

80) Which of the following conditions is not true when a multicoil array probe is used in a surface-scanning application? a. It should improve the detection of small-volume discontinuities b. It can cover larger areas in one pass c. It is only sensitive to discontinuities open to the inspection surface d. It could decrease part inspection time

c. It is only sensitive to discontinuities open to the inspection surface

81) Data from the absolute technique using ID bobbin coils would be least sensitive to: a. long, gradually tapering discontinuities b. one-sided erosion c. short small-volume discontinuities d. large-volume localized wall loss

c. short small-volume discontinuities

82) Self-comparison differential channels would be best for the detection of: a. long tapered discontinuities b. short abrupt discontinuities c. temperature differences d. slow-changing tube wall thickness

b. short abrupt discontinuities

83) The fill factor is a ratio that is: a. identical to the liftoff of a surface coil b. always greater than one (1) c. ideally 3:1 d. always less than one (1), or 100%

d. always less than one (1), or 100%

84) Which of the following is not applicable to eddy current testing? a. It can be used to provide high sensitivity to small discontinuities b. It can be used for high-speed testing c. It can be used to measure coating thicknesses d. It can measure material thicknesses up to 102 mm (4 in.)

d. It can measure material thicknesses up to 102 mm (4 in.)

85) A secondary magnetic field produced by eddy currents induced in a nonmagnetic conductor close to the inducing coils: a. induces a magnetic field parallel to the surface b. aids the coil's magnetic field c. opposes the coil's magnetic field d. decreases the frequency of the current

c. opposes the coil's magnetic field

86) A test specimen used as a basis for calibrating test equipment or as a comparison when evaluating test results is referred to as a: a. null-balancer b. phase shifter c. reference standard d. high-pass filter

c. reference standard

87) The process of comparing the reading or output of an instrument, device, or dial with a standard to determine the instrument's accuracy, capacity, or graduations is referred to as: a. calibration b. differentiation c. integration d. phase shifting

a. calibration

88) Figure 1 is an illustration of a material's: a. phase analysis loop b. sine wave c. hysteresis loop d. impedance plane diagram

c. hysteresis loop

89) Ferromagnetic materials that have been magnetically saturated to suppress permeability variations may retain a certain amount of the magnetization. This is called: a. coercive force b. residual magnetism c. hysteresis loop d. hysteresis loss

b. residual magnetism

90) An alternating current flowing in a conductor will set up: a. an alternating current field around the conductor b. a periodically changing voltage tangent to the conductor c. an alternating magnetic field both inside and around the conductor d. a piezoelectric effect

c. an alternating magnetic field both inside and around the conductor

91) Which of the following is determined by the length of wire used to wind a coil? a. Specific resistance b. Resistance c. Frequency of the applied AC current d. Voltage of the applied AC current

b. Resistance

92) The region around a magnet that attracts pieces of iron or steel is called: a. a maxwell b. retentivity c. the magnetic field d. alternating current

c. the magnetic field

93) Inspection requiring the test object to be loaded and/or sectioned to verify and/or establish mechanical or physical properties is known as: a. impedance testing b. phase analysis testing c. destructive testing d. nondestructive testing

c. destructive testing

94) The depth of penetration would ____ if the localized permeability of a material increased. a. increase b. decrease c. remain constant d. increase the conductivity

b. decrease