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نماذج NE461

Department of Nuclear Engineering

Nondestructive Testing (NE 461)

Fall 2015 Final Exam

Eddy Current Testing

Q-I Circle the best choice in the following questions:

Since eddy current signals are affected by many different variables, it is particularly important to use what when setting up the equipment?
A. Couplant C. Reference standards

B. Fluorescent particles D. Non abrasive cleaners
HPF stands for:
A. High Pulse Filter C. High Pass Filter

B. Harmonic Pulse Filter D. High Pulse Factor
LPF stands for:
A. Low Pulse Frequency C. Last Pass Filter

B. Low Pass Filter D. Low Pass Frequency
Filters are adjusted in:
1. Hz C. MHz
2. KHz D. THz
Which type of probe is most often used to inspect the inside diameter of a machined hole?
1. Pencil probes C. Bolt hole probes
2. Surface probes D. Bobbin probes
Inductance is identified by the letter:
A. (L) C. (Z)

B. (M) D. (X)
When a probe is brought near a conductive but nonmagnetic material, the coil's inductive reactance will:
A. Increase C. Remain the same

B. Decrease D. Remain the same until the probe touches the material
Some common classifications of probes include:
1. Surface probes C. ID probes l
2. Bolt hole probes D. All of the before
Pencil probes are prone to:
A. Energy spikes C. Wobble

B. Low frequency noise D. Both A and C
The HPF allows:
1. Low frequencies to pass and filters out the high frequencies
2. High frequencies to pass and filters out the low frequencies
3. For the combined frequencies to be adjusted to a harmonic balance
4. The shape of the waveform to be clipped beyond it frequency balance
Scanning speed must be controlled:
1. When using a small transducer C. When using a high pass filter
2. When using a large transducer D. When using a large low frequency probe
The HPF is used to:
1. Eliminate low frequencies which are produced by slow changes, such as a conductivity shift
2. Adjust the bandwidth to a neutral frequency in order to maximize depth of penetration
3. Remove any standing waves in the output signal
4. Shift the waveform from positive to negative when a rejectable defect is identified
5. None of them
Use of the HPF is not recommended:
1. On thin parts C. When scanning manually
2. On thick parts D. On ferrous parts
The higher the frequency of the current used to drive the probe, the:
1. More effective shielding will be due to skin effect
2. Deeper the eddy currents will penetrate
3. Stronger the probe's magnetic field will be
4. Both A and C E. none of them
Probes for inspection of pipe and tubing are typically of the:
A.       Surface probe variety

B.       Bolt hole variety

C.       Bobbin (ID) variety

D.       All of them                                                                  E.             None of them
When an absolute probe is brought near a ferromagnetic material, the inductive reactance of the coil will:
                A.            Remain unchanged

                B.            Increase because the material will concentrate the magnetic field in and around the coil

                C.            Decrease because the material will concentrate the magnetic field in and around the coil

                D.            Decrease because the magnetic field of the coil will be weakened by the material
A probe that is often intended to be used in contact with the test surface is called a:
A. Reference probe C. Transmission probe

B. Surface probe D. Reflection probe
When using the lift-off trace of an impedance plane instrument to distinguish between several materials with high electrical conductivity, it is best to test using a:
A. High frequency C. Low frequency

B. Variable frequency D. None of them
Which type of probe has a long slender housing to permit inspection in restricted spaces:
1. Pancake probes C. Encircling probes
2. Pencil probes D. Sliding probes
A probes that can be used to inspect the entire circumference of test objects are:
1. Encircling or bobbin probes C. Pencil probes
2. Circumference probes D. None of them
Which type of probe is most commonly sued to inspect solid products such as bar stock?
1. Bobbin probes C. Encircling coils
2. Surface coils D. Pencil probes
The higher the inductance of a coil at a given frequency:
1. The more penetrating the eddy currents will be C. The more sensitive the coil will be
2. The less sensitive the coil will be D. None of them
When testing for subsurface flaws, the frequency should be:
1. As high as possible
2. As low as possible
3. Calculated to produce a 90^o difference between the lift-off and flaw signals
4. None of them
Probe shielding and loading are sometimes used to:
1. Prevent external electrical interference C. Magnetically saturate the part
2. Limit the spread and concentrate the magnetic field of the coil D.None of them
What material(s) is/are commonly used to shield an eddy current probe?
1. Ferrite C. Lead
2. Aluminum D. Both A and B
Probes with iron cores tend to:
1. Be more sensitive than air core probes and less affected by probe wobble
2. Be more difficult to use D. Both B and C
3. Increase the background noise of the signal E. All of them
The coil in an eddy current probe is most often made from:
1. Iron D. Platinum
2. Copper E. all of them
3. Silver
Inductance is caused by:
1. The interaction of a changing magnetic field with a conductor
2. Direct current D. None of them
3. Resistance in the coil E. All of them
An eddy current test circuit will have:
1. Resistance D. Both A & B
2. Inductive reactance E. All of them
3. A small amount of capacitance
Eddy current testing can be used to:
1. Detect surface and near surface cracks D. Both A & B
2. Measure electrical conductivity E. All of them
3. Measure the thickness of nonconductive coatings on plastics

Which component features should be similar to the reference standard?
A. Material thickness C. Material conductivity
B. Material geometry D. All of the before
Which of the following are a common eddy current reference standard?
A. Conductivity standards C. Hole discontinuity standards

B. Tube discontinuity standards D. All of the before
The principles of operation of the most commonly used eddy current instruments are based on:
A. Roentgen's formulas C. Reciprocity

B. Maxwell's inductance bridge D The Inverse Square Law
In almost all cases, eddy current inspection procedures require the equipment to be calibrated to:
1. A reference standard C. A crack which is the rejection criteria
2. An identified defect D. A crack twice the rejection criteria
Drilled holes are commonly used to represent:
1. Pitting C. Delaminations
2. CracksD. Nn of the before
The main purpose of an iron core in a probe is to:
A.            Shift the transmission of eddy currents in order to decrease penetration

B.             Allow the probe to operate at a higher frequency

C.             Concentrate the magnetic field near the center of the probe
D.             Allow testing of very dense materials
Filtering is applied to the received signal and, therefore:
1. It should be added to the base signal
2. It is not directly related to the probe drive frequency
3. Should be added to the pick-up coil time
4. Should be subtracted from the amplitude of the dB
Wide surface probes are used when scanning:
A. Large areas for very small cracks C. Large areas for relatively large defects

B. Small areas for delaminations D. None of the before
The main function of the LPF is to:
1. Control probe wobble
2. Adjust the machine to the proper conductivity standard
3. Shift the waveform to the left of the screen
4. Remove high frequency interference noise
Probe shielding is used to:
1. Shape the eddy currents to the curvature of the part
2. Reduce the inductive coupling of the probe and part
3. Increase the probe impedance
4. Reduce the effects of nonrelevant features in close proximity to the probe
When testing for surface flaws, the probe drive frequency used:
A.    Should be as high as possible                                    D.   Depends only on the material conductivity

B.    Should be as low as possible                                     E.    None of them

C.    Depends on the conductivity and permeability of the material
Sliding probes are used to test:
1. Large flat surfaces C. In radiuses
2. Inside bolt holes D. Around the edges of fasteners
Sliding probes usually operate in the:
1. Reflection mode C. Pulsed mode
2. Through-transmission mode D. Differential mode
When making a conductivity measurement, the thickness of the material should be at least ___ times the standard depth of penetration.
1. One C. Three
2. Two D. Four
The depth of penetration is affected by:
1. Magnetic permeability C. Probe drive frequency
2. Electrical resistivity D. All of them
A bolt hole probe and scanner is used to inspect:
1. Flat surfaces D. Both B and C
2. Radiuses E. All of them
3. Holes

Narrow EDM notches and saw cuts:
1. Are never used because they are too wide C. Are commonly used to represent cracks
2. Are never used due to their heat affected zones D. Both A and B

Most surface probe coils are wound so that:
A.   They transmit a frequency that will slightly resonate the part surface

B.   They create a static magnetic field

C. The axis of the coil is perpendicular to the test surface

D.   Both B and C                                                                                                E.            all of them.

Discontinuities, such as delaminations, that are in a plane that is parallel with the test surface will likely:
1. Be easily detected with a surface probe D. Be easily detected with an external probe
2. Be easily detected with an internal probe E. None of them
3. Be easily detected with an external probe

When maintaining constant liftoff is a problem, what type of probe should be used?
1. A absolute probe D. Both A and C
2. A differential probe E. Both B and C
3. A reflection probe

Experiment

Generate a family of liftoff curves for the different materials available in the applet using a frequency of 10kHz. Note the relative position of each of the curves. Repeat at 500kHz and 2MHz. (Note: it might be helpful to capture an image of the complete set of curves for each frequency for comparison.)

1) Which frequency would be best if you needed to distinguish between two high conductivity materials?

2) Which frequency would be best if you needed to distinguish between two low conductivity materials?

The impedance calculations in the above applet are based on codes by Jack Blitz from "Electrical and Magnetic Methods of Nondestructive Testing," 2nd ed., Chapman and Hill.

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