NE461 Exam Samples

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:

 

  1. 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

     

  2. HPF stands for:

    A.        High Pulse Filter                                                       C.         High Pass Filter

    B.        Harmonic Pulse Filter                            D.         High Pulse Factor

  3. LPF stands for:

    A.   Low Pulse Frequency                                                    C.             Last Pass Filter                      

    B.   Low Pass Filter                                                               D.            Low Pass Frequency

     

  4. Filters are adjusted in:
    1. Hz                                                                            C.         MHz
    2. KHz                                                                         D.         THz

       

  5. 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

       

  6. Inductance is identified by the letter:

          A.      (L)                                                                                   C.             (Z)

          B.       (M)                                                                                  D.            (X)                                     

     

  7. 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

     

  8. Some common classifications of probes include:
    1. Surface probes                                                     C.            ID probes l
    2. Bolt hole probes                                                   D.            All of the before

                     

  9. Pencil probes are prone to:

           A.     Energy spikes                                                              C.             Wobble

           B.      Low frequency noise                                                  D.            Both A and C

     

  10. 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

       

       

  11. 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

       

  12. 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
  13. Use of the HPF is not recommended:
    1. On thin parts                                                         C.            When scanning manually
    2. On thick parts                                                       D.            On ferrous parts

       

  14. 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

       

  15. 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

     

  16. 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

     

  17. 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

     

  18. 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

     

  19. 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

       

  20. 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

       

  21. 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

       

  22. 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

       

  23. When testing for subsurface flaws, the frequency should be:
    1. As high as possible
    2. As low as possible                                       
    3. Calculated to produce a 90o difference between the lift-off and flaw signals
    4. None of them

       

  24. 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

       

  25. What material(s) is/are commonly used to shield an eddy current probe?
    1. Ferrite                                                                             C.   Lead
    2. Aluminum                                                                     D.   Both A and B

       

  26. 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

       

  27. The coil in an eddy current probe is most often made from:
    1. Iron                                                                                D.     Platinum
    2. Copper                                                                           E.      all of them
    3. Silver

       

  28. 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

       

  29. 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

       

  30. 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

       

  1. Which component features should be similar to the reference standard?

                     A.         Material thickness                                 C.        Material conductivity
                     B.         Material geometry                                 D.   All of the before

     

  2. 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

     

  3. 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

     

  4. 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

       

  5. Drilled holes are commonly used to represent:
    1. Pitting                                                                                     C.             Delaminations
    2. CracksD.            Nn of the before

       

  6. 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

     

  7. 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

       

  8. 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

     

  9. 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

                     

  10. 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

       

  11. 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

     

  12. Sliding probes are used to test:
    1. Large flat surfaces                                                      C.            In radiuses
    2. Inside bolt holes                                                           D.            Around the edges of fasteners

       

  13. Sliding probes usually operate in the:
    1. Reflection mode                                                          C.            Pulsed mode
    2. Through-transmission mode                                     D.            Differential mode
  14. 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

       

  15. The depth of penetration is affected by:
    1. Magnetic permeability                                                               C.       Probe drive frequency
    2. Electrical resistivity                                                                     D.            All of them

       

  16. 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
  1. 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

       

  1. 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.

     

  1. 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

       

  1. 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.


Last Update
2/7/2016 2:20:53 PM