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
- 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
- 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.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
- 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.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
- 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.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
- 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
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