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1. A method of minimizing the effect of indications cause by gradual dimesional changes while retaining the indications cause 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 of the above
3. In oder to decrease the effect on conductivity reading due to varations 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 decreasimg this effect
4(5). A term used to describe the effects 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
5. A term used 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 one of the above
6. The fill factor when a 13 mm (0.5 in.) diameter bar is inserted in a 25 mm (1 in.) diameter coil is:
a. 0.5 (50%)
b. 0.75 (75%)
c. 1.0 (100%)
d. 0.25 (25%)
7. The impedance change in the test part characterstics can be most easily analyzed as a combine change in:
a. capacitve reatance and resistance
b. harmonic frequencies and inductive reactance
c. signal amplitude and phase
d. retentivity and harmonic frequecies
8. A term used to define two or more coils electrically connected in opposition such that any electromagnetic condition which is not common to both test specimen and a reference specimen will produce an unbalance in the system is:
a. differential
b. absolute
c. laminar
d. flying probes
9. When testing small parts in an eddy current encircling coil for permeability measurements, which of the following test parameters may be considerd important?
a. length of the test sample
b. thickness of the test sample
c. cross-sectional area of the test sample
d. all of the above
10. In test coil consisting of both a primary and secondary winding, the voltage across the secondary is a function of:
a. test material permeabilty
b. test frequency
c. geometry of the test object
d. all of the above
11. Eddy current testing relies on the principle of:
a. magnetostriction
b. electomagnetic induction
c. piezoelectric energy conversion
d. magnetomotive force
12. 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. hystersis loss
13. The three major specimen parameters that 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
14. A term used to define an instrumentation technique that discriminates between variables in the test part by the different phase angle changes which these conditions produced in the test signal is:
a. phase distortion
b. phase shifting
c. phase discrimination
d. phase analysis
15. If the characteristic frequency (fg) of a material os 125 Hz, the test frequency required to give an f/fg ratio of 10 would be:
a. 1.25 Hz
b. 12.5 Hz
c. 1.25 kHz
d. 12.5 kHz
16. A term used to define any change in a sinusoidal signal when the output is not a linear reprodution of the input is:
a. distortion
b. linearity
c. phase shifting
d. dynamic range
17. At a fix test frequency, in which of the following materials will the eddy current penetration be greatest?
a. aluminum (35 percent IACS conductivity)
b. brass (15 percent IACS conductivity)
c. copper ( 95 percent conductivity)
d. lead (7 percent conductivity)
18. The magnetic domains in an unmagnetized ferromagnetic material are:
a. arranged to facilitate the conduction of electrons
b. randomly oriented and neutralize each other
c. uniformly oriented
d. create a major north and south pole in the material
19. The atom of a metal showing magnetic characteristics are grouped inti regions that are the smallest known permanent magnets. These regions are called:
a. lattice structures
b. cells
c. domains
d. planetary spins
20. If the test frequency increases while the field strength is held constant, the surface eddy current density:
a. decreases
b. increases
c. remains the same
d. could do any of the above
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
22. When eddy current testing a nonferrous material, the choice of test frequency is determined by the:
a. degree of phase discrimination required
b. eddy current penetration needed
c. rate of response required
d. all the above
23. The flux density in a magnetic material is usually designated by the:
a. symbol u
b. symbol o
c. letter B
d. letter H
24. 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
25. 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
26. The thickness of nonconductive coating on a conductive base can be most simply measured by:
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.
27. which of the followng is not a factor that affects the inductance of an eddy current test coil?
a. diameter of coil
b. test frequency
c. overall shape of the coils
d. distance from other coils
28. 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
29. lt 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 the above methods of testing
30. 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 a cathode ray tube
b. an ellipse on a cathode ray tube
c. a null reading on a meter
d. a clean base line on a strip chart
31. when eddy current testing by the ellipse method, one variable may be indicated by the angle of 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
32. 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 above
33.The ratio of the specifc 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
34. which of the following materials would be more likely used as a mounting material for a probe coil?
a. aluminum
b. fiberglass
c. copper
d. steel
35. 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 is called:
a. air flux
b. leakage flux
c. induced flux
d. none ofthe above
36. A term used to define a material having a permeability less than of a vacuum is:
a. diamagnetic
b. ferromagnetic
c. paramagnetic
d. magnetic
37. The inductive reactance of a coil is measured in units of:
a.mhos
b. ohms
c. henrys
d. gauss
38. 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 combination of the quantities listed above
39. For age hardenable aluminum and titanium alloys, changes in hardness are indicated by changes in:
a. retentivity
b. permeability
c. conductivity
d. magnetostriction
40. 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 decreade.
41. The ratio of a material's flux density to a test coil's magnetizing force, (B/H), can be used to determine the material's:
a. conductivity
b. resistivity
c. lift-off
d. permeability
42. Which of the following conditions are 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 pieces to be tested
d. if the material is aluminum, the surface should be anodized
43. The symbol commonly used to signify impedance is:
a. Z
b. XfE
c. R
d. Xc
44. 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
45. When a rod is placed in an encircling type of coil, the density of eddy currents will be the greatest:
a. at the surface
b. at the center
c. midway between the surface and the center
d. none of the above
46. The actual frequencies used in any specific eddy current inspection should be selected on 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 the above
