Eddy Current Practise
Theory and application of non destructive testing method eddy current
- 1.
A method of minimizing the effect of indications caused by gradual dimensional changes whileretaining 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
Correct Answer
A. Include a high pass filter in the eddy current test equipment -
- 2.
Which of the following methods may be used to improve the signal-to-noise ratio of an eddycurrent test system?
- A.
Filtering or differentiation
- B.
Phase discrimination
- C.
Intergration
- D.
All 3 are correct
Correct Answer
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
Correct Answer
A. The test frequency should be increased -
- 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 degress out of the phase with current in the coil
Correct Answer
B. Perpendicular to the major plane of the discontinuity -
- 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
Correct Answer
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
Correct Answer
A. Skin effect -
- 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%)
Correct Answer
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
Correct Answer
B. Nonlinearity -
- 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
Correct Answer
A. Low pass filter -
- 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:
- A.
Capacitive reactance and resistance
- B.
Harmonic frequencies and inductive reactance
- C.
Signal ampllitude and phase
- D.
Retentivity harmonic frequencies
Correct Answer
C. Signal ampllitude and pHase -
- 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
Correct Answer
C. Xr = 2 pie fL -
- 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
Correct Answer
B. Impedance of the pickup coil -
- 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
Correct Answer
A. Differential -
- 14.
Tubing is generally inspected using:
- A.
U-Shaped coils
- B.
Gap coils
- C.
Encircling coils
- D.
None of the answers
Correct Answer
C. Encircling coils -
- 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
Correct Answer
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
Correct Answer
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
Correct Answer
B. Electromagnetic induction -
- 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
Correct Answer
B. Residual Magnetism -
- 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
Correct Answer
A. Coercive force -
- 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
Correct Answer
C. Electrical conductivity, permeability, and material geometry -
- 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
Correct Answer
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
Correct Answer
B. Test frequency divided by limit frequency -
- 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
Correct Answer
B. The pHase of the OD discontinuity leads the pHase of the ID discontinuity -
- 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
Correct Answer
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
Correct Answer
C. 1.25 kHz -
- 26.
At a fixed test frequency, in which of the following materials will the eddy currentpenetration be greatest?
- A.
Aluminum (35% IACS conductivity)
- B.
Brass (15% IACS conductivity)
- C.
Copper (95% IACS conductivity)
- D.
Lead (7% IACS conductivity)
Correct Answer
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
Correct Answer
B. Magnetically saturating the test specimen -
- 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
Correct Answer
A. Distortion -
- 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
Correct Answer
B. Increases -
- 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
Correct Answer
C. Decrease -
- 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
Correct Answer
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
Correct Answer
B. Randomly oriented and neutralize each other -
- 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
Correct Answer
A. Induction -
- 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
Correct Answer
B. Normalized -
- 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
Correct Answer
C. Impedance-magnitude 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
Correct Answer
A. Small discontinuities -
- 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
Correct Answer
C. Large number of known or unknown variables which appear in the output indication -
- 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
Correct Answer
C. Domains -
- 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
Correct Answer
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
Correct Answer
C. Letter B -
- 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
Correct Answer
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
Correct Answer
C. The coil's magnetic field -
- 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
Correct Answer
A. Observing the lift-off effect caused by the coating -
- 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
Correct Answer
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
Correct Answer
B. Test frequency -
- 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
Correct Answer
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
Correct Answer
C. Can exist in both the primary and secondary windings of an eddy current coil -
- 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
Correct Answer
C. Spinning 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
Correct Answer
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
Correct Answer
C. The pHase analysis method of testing -
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Mar 22, 2022Quiz Edited by
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Apr 06, 2010Quiz Created by
Ndtputz
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