Free ASNT Eddy Current Questions and Answers — Questions and Answers
Question 1: A method of minimizing the effect of indications caused by gradual dimensional changes while retaining the indications caused by discontinuities is to:
- Include a high pass filter in the eddy current test equipment (Correct answer)
- Include a low pass filter in the eddy current test equipment
- Increase the bandpass of the amplifier
- Use the impedance method of testing
Correct answer: Include a high pass filter in the eddy current test equipment
Explanation: <br> Including a high pass filter in the eddy current test equipment allows the system to filter out low-frequency signals, which are typically associated with gradual dimensional changes, while retaining high-frequency signals, which are indicative of discontinuities. This helps minimize the effect of gradual dimensional changes while focusing on detecting relevant indications of defects.
Question 2: Which of the following methods may be used to improve the signal-to-noise ratio of an eddy current test system?
- Filtering or differentiation
- Phase discrimination
- Integration
- All of the above (Correct answer)
Correct answer: All of the above
Explanation: <br> All of the methods listed—filtering or differentiation, phase discrimination, and integration—can be used to improve the signal-to-noise ratio of an eddy current test system. Filtering or differentiation helps in separating relevant signals from noise by filtering out unwanted frequencies or by differentiating the signal. Phase discrimination involves comparing the phase of the reference signal with that of the test signal to enhance sensitivity to changes in material properties. Integration can improve signal quality by summing up signal values over time to enhance the detectability of small changes in the signal.
Question 3: In order to decrease the effect on conductivity readings due to variations in test part thickness:
- The test frequency should be increased (Correct answer)
- The test frequency should be decreased
- The fill factor should be decreased
- There is no practical method for decreasing this effect
Correct answer: The test frequency should be increased
Explanation: <br> To decrease the effect on conductivity readings due to variations in test part thickness, increasing the test frequency is a practical method. Higher frequencies are less affected by changes in material thickness compared to lower frequencies. Therefore, increasing the test frequency helps minimize the influence of variations in test part thickness on conductivity readings.
Question 4: When testing by the eddy current method, discontinuities will be most easily detected when the eddy currents are:
- Coplanar with the major plane of the discontinuity
- Perpendicular to the major plane of the discontinuity (Correct answer)
- Parallel to the major plane of the discontinuity
- 90 degrees out of phase with the current in the coil
Correct answer: Perpendicular to the major plane of the discontinuity
Explanation: <br> Discontinuities will be most easily detected when the eddy currents are perpendicular to the major plane of the discontinuity. This orientation maximizes the interaction between the eddy currents and the material, leading to more significant changes in the impedance or other parameters being measured by the eddy current testing equipment.
Question 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 them is varied is:
- Fill factor
- Edge effect
- End effect
- Lift-off (Correct answer)
Correct answer: Lift-off
Explanation: <br> Lift-off is the 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 them is varied. This effect can influence the signal response in eddy current testing and needs to be carefully managed to ensure accurate results.
Question 6: A term used to define the phenomenon where, at very high frequencies, the eddy current flow is restricted to an extremely thin outer layer of the conductor is:
- Skin effect (Correct answer)
- High-frequency filtration
- Low-frequency filtration
- All of the above
Correct answer: Skin effect
Explanation: <br> The term used to define the phenomenon where, at very high frequencies, the eddy current flow is restricted to an extremely thin outer layer of the conductor is "Skin effect." This effect causes the current density to be highest at the surface of the conductor and decreases exponentially as depth increases into the material.
Question 7: The term used to define the difference between actual instrument output and expected output as defined by a straight-line calibration curve is:
- Phase shift
- Nonlinearity (Correct answer)
- Lift-off
- Skin effect
Correct answer: Nonlinearity
"Explanation: <br> The term used to define the difference between actual instrument output and expected output as defined by a straight-line calibration curve is "Nonlinearity." In a perfect linear system, the instrument output would precisely match the expected output defined by a straight-line calibration curve. However, in reality, nonlinearity can occur, leading to deviations from this ideal behavior.
Question 8: Which of the following could be used to suppress unwanted high-frequency harmonics?
- Low-pass filter (Correct answer)
- Oscillator
- Phase discriminator
- High-pass filter
Correct answer: Low-pass filter
Explanation: <br> A low-pass filter can be used to suppress unwanted high-frequency harmonics by allowing only low-frequency signals to pass through while attenuating higher-frequency signals. This helps in filtering out unwanted noise or harmonics, thereby improving the quality of the signal.
Question 9: A term used to define two or more coils electrically connected in opposition such that any electromagnetic condition which is not common to both a test specimen and a reference specimen will produce an unbalance in the system is:
- Differential (Correct answer)
- Absolute
- Laminar
- Flying probes
Correct answer: Differential
Explanation: <br> In the context described, a setup where two or more coils are electrically connected in opposition to each other is referred to as a "differential" arrangement. This arrangement is designed to detect any electromagnetic conditions that are not common to both the test specimen and a reference specimen. The system is balanced when the conditions are identical, and any deviation from this balance indicates a difference between the two specimens being tested.
Question 10: Tubing is generally inspected using:
- U-shaped coils
- Gap coils
- Encircling coils (Correct answer)
- None of the above
Correct answer: Encircling coils
Explanation: <br> Tubing is generally inspected using encircling coils. Encircling coils are designed to wrap around the circumference of the tubing or pipe being inspected. This configuration allows for comprehensive coverage and detection of defects throughout the entire circumference of the tubing.
Question 11: When testing small parts in an eddy current encircling coil for permeability measurements, which of the following test parameters may be considered important?
- Length of the test sample
- The thickness of the test sample
- Cross-sectional area of the test sample
- All of the above (Correct answer)
Correct answer: All of the above
Explanation: <br> All of the test parameters listed (length, thickness, and cross-sectional area) are important when testing small parts in an eddy current encircling coil for permeability measurements. Each parameter affects the behavior of the eddy currents and the sensitivity of the measurements, making them all essential considerations.
Free ASNT Eddy Current Questions and Answers
A method of minimizing the effect of indications caused by gradual dimensional changes while retaining the indications caused by discontinuities is to: