Eddy Current Practise
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Theory and application of non destructive testing method eddy current
- 1.
- 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.
- A.
Filtering or differentiation
- B.
Phase discrimination
- C.
Intergration
- D.
All 3 are correct
- 3.In order to decrease the effect on conductivity readings due to variations in test part thickness:
- A.
The test frequency should be increased
- B.
The test frequency should be decreased
- C.
The fill factor should be decreased
- D.
There is no practical method for decreasing this effect
- 4.
- 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 degress out of the phase with current in the coil
- 5.A term used to describe the effect observed due to a change in the electromagnetic coupling between a test specimen and a probe coil when the distance of separation between themis varied is:
- A.
Fill 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 resrticted to an extremely thin outer layer of the conductor is:
- A.
Skin effect
- B.
High frequency filtration
- C.
Low frequency filtration
- D.
Any of these answers
- 7.The fill factor when a 1/2 inch diameter bar is inserted in a 1 inch diameter coil is:
- A.
0.5 (50%)
- B.
0.75 (75%)
- C.
1.0 (100%)
- D.
0.25 (25%)
- 8.The term used to define the difference between actual instrument output and expectedoutput as defined by a straight line calibration curve is:
- A.
Phase shift
- B.
Nonlinearity
- C.
Lift off
- D.
Skin effect
- 9.Which of the following could be used to suppress unwanted high frequency harmonics?
- A.
Low pass filter
- B.
Oscillator
- C.
Phase discriminator
- D.
High pass filter
- 10.
- A.
Capacitive reactance and resistance
- B.
Harmonic frequencies and inductive reactance
- C.
Signal ampllitude 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 detectedas variations in:
- A.
Test speed
- B.
Impedance of the pickup coil
- C.
None of the 2 answers
- D.
Both answers are correct
- 13.A term used to define 2 or more coils electrically connected in opposition such that any electromagentic condition which is not common to both a test specimen and areference specimen will produce an unbalance in the system is:
- A.
Differential
- B.
Absolute
- C.
Laminar
- D.
Flying probes
- 14.Tubing is generally inspected using:
- A.
U-Shaped coils
- B.
Gap coils
- C.
Encircling coils
- D.
None of the answers
- 15.When testing small parts in an eddy current encircling coil for permeability measurements,which of the following test parameters may be considered important?
- A.
Length of the test sample
- B.
Thickness of the test sample
- C.
Cross-sectional area of the test sample
- D.
All answers are correct
- 16.In a test coil consisting of both a primary and secondary winding, the voltage across thesecondary 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 Bvalue when H has returned to zero is:
- A.
Coercive force
- B.
Residual Magnetism
- C.
Saturation value
- D.
Hysteresis loss
- 19.The term used to define the value of H field required to decrease the remanence of a material to zero is:
- A.
Coercive force
- B.
Magnetizing force
- C.
Back emf
- D.
The overlap value
- 20.The 3 major specimen parameters which influence eddy current testing are:
- A.
Electrical conductivity, frequency, and material geometry
- B.
Density, permeability, and frequency
- C.
Electrical conductivity, permeability, and material 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
- 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.
- 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 conditionsproduce in the test signal is:
- A.
Phase distortion
- B.
Phase shifting
- C.
Phase discrimination
- D.
Phase analysis
- 25.If the characteristic frequency (fq) of a material is 125 hz, the test frequency required to give an f/fq ratio of 10 would be:
- A.
1.25 Hz
- B.
12.5 Hz
- C.
1.25 kHz
- D.
12.5 kHz
- 26.
- A.
Aluminum (35% IACS conductivity)
- B.
Brass (15% IACS conductivity)
- C.
Copper (95% IACS conductivity)
- D.
Lead (7% IACS conductivity)
- 27.The heating effect in magnetic materials caused by work required to rotate magneticdomains can be eliminated by:
- A.
Increasing the rate of displacement of the specimen through the 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
- 28.A term used to define any change in a sinusoidal signal when the output is not a linearreproduction 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 producedby a given chaange in conductivity will:
- A.
Increase
- B.
Remain the same
- C.
Decrease
- D.
Could do any of the 3
- 31.Which of the following would be easier to detect in tubing by the eddy currentmethod using self comparison differential coil arrangement?
- A.
Gradual changes in 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
- 34.To eliminate any dependence upon the number of turns of a test coil, the inductancevalues 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 totalcoil 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
- 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 whichare the smallest known permanent magnets. These regions are called:
- A.
Lattice structures
- B.
Cells
- C.
Domains
- D.
Planetary spins
- 39.
- 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
- 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
- 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.
- 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
- 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
- 49.A term used to define an eddy current test coil which uses magnetic material to purposelyshape 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 anddimensional 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
- 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.
- 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
- 55.When eddy current testing by the linear time-base method, what is applied to the verticaldeflection plates of a cathode ray tube when a condition of unbalance exist between the test specimen and the reference standard?
- A.
A sinusoidal 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
- 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 pprocessingat 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
- 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 dueto 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
- 64.A term used to define a material having a permeability less than that of a vacum is
- A.
Diamagnetic
- B.
Ferromagnetic
- C.
Paramagnetic
- D.
Magnetic
- 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
- 67.Which of the following conditions is not important when selecting specimens to be usedas reference standards?
- A.
The specimen should be of the same size and shape as the 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 variablesof 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
- 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
- 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 theirmaximums 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
- 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), can beused 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
- 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
- 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. Totest all specimens of similar geometry under the same condition, it is only necessary to choose a test frequency, (f), so that frequency ratio f/f lies at the same point on the impedance diagram for each specimen. This principle is based upon:
- A.
Ohm's law
- B.
Kirchoff's law
- C.
The Similarity Law
- D.
None of these
- 85.To be useful, limit frequency equations must be:
- A.
Used with their impedance 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
- 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 esolution
- D.
Higher penetrability of these materials
- 91.The actual frequency used in any specific eddy current inspection should be selectedon the basis of the:
- A.
Thickness of the material
- B.
Desired depth of 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 testfrequency 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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