# Eddy Current Practise

92 Questions | Total Attempts: 1706  Settings  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.

• 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.

• D.

• 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.

• 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.

• 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.

• 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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