A method of minimizing the effect of indications caused by gradual dimensional changes while retaining the indications caused by discontinuities is too:
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.
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.
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.
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 phase with the current in the coil.
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.
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.
The fill factor when a 1/2-inch diameter bar is inserted in a 1-inch diameter coil is:
A. 0.5 or (50%)
B. 0.75 or (75%)
C. 1.0 or (100%)
D. 0.25 or (25%)
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.
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.
The impedance change of an eddy current test coil due to a change in 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 and harmonic frequencies.
The inductive reactance of a test coil can be calculated using the formula:
A. XL = 2 π L
B. XL = 1/2 π L
C. XL = 2 π f L
D. XL = W 2 π f
When conducting an eddy current test, variations in the test material can be detected as variations in:
A. test speed.
B. impedance of a pickup coil.
C. none of the above.
D. all of the above.
A term used to define two or more coils electrically connected in opposition such that any electromagnetic 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.
Tubing is generally inspected using:
A. U-shaped coils.
B. internal coils.
C. encircling coils.
D. Either B or C depending on configuration.
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.
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.
Eddy current testing relies on the principle of:
A. magnetostriction.
B. electromagnetic induction.
C. piezoelectric energy conversion.
D. magnetomotive force.
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.
The term used to define the value of H field required to decrease the remanence of a material to zero is:
B. magnetizing force.
C. back emf.
D. the overlap value.
The three 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.
Doubling the number of turns on a coil will:
A. double the indicators.
B. halve the inductance.
C. decrease the inductance by a factor of four.
D. increase the inductance by a factor of four.
Frequency ratio, f/fg 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 of these.
D. both of these.
When testing tubing, using and 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.
A term used to define an instrumentation technique which 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.
If the characteristic frequency (fg) of a material is 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.
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
At a fixed 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 IACS conductivity)
D. Lead (7 percent IACS conductivity)
The heating effect in magnetic materials caused by the 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 through the test coil.
D. testing in an air-conditioned room.
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.
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.
Which of the following would be easier to detect in tubing by the eddy current method using the self-comparison differential coil arrangement?
A. Gradual changes in diameter.
B. Gradual changes in conductivity.
C. Changes in temperature.
D. Short flaws.
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.
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.
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 above.
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.
When eddy current testing tubing with a system that includes a frequency discriminating circuit, which of the following variables would we classified as a high-frequency variable?
A. Small discontinuities.
B. Conductivity changes.
C. Diameter changes
D. Wall thickness variations.
A major problem associated with the 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.
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.
When a coil's magnetizing force is applied to a ferromagnetic material, the flux density in 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.
The flux density in a magnetic material is usually designed by the:
A. Greek symbol “μ” (mu)
B. Greek symbol “∆” (delta)
C. letter B
D. letter H
The magnetizing force of an eddy current test coil is usually designated by the:
The thickness of nonconductive coatings 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.
The use of magnetic shielding around the exciting coil will generally:
A. increase the magnetic field extension but decreases 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.
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.
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. exists only in the test specimen.
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.
A term used to define an eddy current test coil which uses magnetic material to purposely shape the magnetic field is:
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.
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 the above methods of testing.
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.
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.
When eddy current testing by the linear time-base method, what is applied to the vertical deflection plates of a cathode 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 sinusoidal wave 90 degrees out of phase with the timing voltage.
C. A sawtooth waveform.
D. Zero net voltage.
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 exists between the test specimen and the reference standard?
A. A sinusoidal wave
B. A sawtooth wave
C. A square wave
D. No voltage
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.
The ratio of the specific diameter of a probe to the minimum discontinuity of interest should be:
A. less then 2.
B. greater than 2.
C. greater than 4.
D. greater than 10.
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
A term used to define a surface or internal rupture which is attributed to processing at too low a temperature or excessive working or metal movement during the forging, rolling, or extruding operation is:
A. cold shut.
B. microshrinkage.
C. burst.
D. inclusion.
A term used to define the timing relationships involved in alternating current signals is:
A. magnitude.
B. phase.
C. impedance.
D. reactance.
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.
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.
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.
A term used to define a material having a permeability less than that of a vacuum is:
A. diamagnetic.
B. ferromagnetic.
C. paramagnetic.
D. magnetic.
The inductive reactance of a coil is measured in units of:
A. mhos.
B. ohms.
C. henrys.
D. gauss.
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
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 piece to be tested.
D. If the material is aluminum, the surface should be anodized.
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.
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 of a combination of the quantities listed above.
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.
The symbol commonly used to signify impedance is:
A. Z
B. X
C. R
D. Xc
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.
If the conductivity of a test part in an eddy current test coil decreases, the magnitude of the eddy currents at a given depth in the test specimen:
A. increases.
B. remains the same.
C. decreases.
D. may increase or decrease.
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.
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.
Which of the following materials would have the highest resistivity value?
A. Aluminum with a 42 percent IACS rating.
B. Magnesium with a 37 percent IACS rating.
C. Cast steel with a 10.7 percent IACS rating.
D. Zirconium with a 3.4 percent IACS rating
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.
D. permeability.
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.
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
For age hardenable aluminum and titanium alloys, changes in hardness are indicated by changes in:
A. retentivity.
B. permeability.
C. conductivity.
D. magnetostriction.
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.
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 by 45 degrees.
C. the direction of the eddy currents in the part also reverses.
D. the eddy currents in the part remain the same.
When testing magnetic materials in an 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.
Impedance diagrams have been mathematically derived and experimentally verified for materials of any conductivity and permeability having rectangular, cylindrical, 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/fg 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.
To be useful, limit frequency equation must be:
A. used with their impedance diagrams.
B. used to determine their impedance diagrams.
C. both of these.
D. neither of these.
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.
The term fill factor applies to:
A. a surface coil.
B. coaxial cable.
C. an encircling coil.
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.
Two test coils are often used in a bridge circuit to:
A. eliminate skin effect.
B. determine the differences between a known standard sample.
C. increase the conductivity of the circuit.
D. decrease the system sensitivity.
When inspecting ferromagnetic materials, relatively low frequencies are normally used because of the:
A. low penetrability of these materials.
B. higher resolution.
C. lower resolution.
D. higher penetrability of these materials.
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.
