Questions and Answers
Variations in the chemical composition of a non-ferromagnetic alloy would have the most effect on its:
Conductivity
A reference sample used to ensure that the amplitude and phase characteristics of a test system do not drift during continuous testing is called a:
Calibration standard
A term used to define a standardized condition in a device or system which results in zero output shown across a bridge circuit is:
Null or Balance
The phenomenon referred to when inspecting products with a uniform cross section and an eddy current signal is produced due to the edge of the product approaching the test coil is called:
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The use of ferromagnetic shielding materials around the AC Coil will generally:
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Eddy current testing can penetrate up to 2 inches in a test part.
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Eddy current always travels:
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Eddy currents cannot be induced in paint.
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Which condition would be the most difficult to detect when using an eddy current testing rod with an encircling coil?
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When conducting an eddy current test using a coil arrangement that compares an external reference standard with the specimen, the system should be nulled or balanced:
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During an eddy current test, discontinuities will be most easily detected when the eddy currents are:
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An eddy current system is least sensitive to discontinuities that:
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A term used to describe a hole, groove, or notch that is machined into the reference standard to provide accurately reproducible quality level is:
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A term used to define one or more turns or loops of a conductor wound in such a manner as to produce an axial magnetic field when current passes through the conductor is:
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A test coil's opposition to the flow of alternating current is called:
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Non-destructive tests aren't conducted to assure large volumes of material are available for sale.
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Determining the instrument control settings needed to pass the highest percentage of the test specimens run is a primary purpose for using a reference standard.
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In order to decrease the effect on conductivity readings due to variations in test part thickness:
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Which product forms would be most applicable to a test using an inside coil?
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The process of comparing the reading or output of an instrument, device, or dial with a standard to determine the instrument's accuracy, capacity or graduation is referred to as:
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A symbol commonly used to describe permeability:
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A change in probe speed will alter the impedance of the coil.
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An eddy current coil arrangement that does not make a comparison with either two sections of the test specimen or one section of the test part and a reference standard is called:
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The impedance of a test coil will increase if the:
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An eddy current test makes use of electrical current induced in a conductive article by:
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Frequency would not be considered to be a material property.
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Determining the exact chemistry of an alloy is not a common application for eddy current testing.
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Which of the following frequencies will provide the greatest eddy current penetration in aluminum?
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Study Notes
Eddy Current Testing NDT Overview
- Variations in chemical composition of non-ferromagnetic alloys primarily affect conductivity.
- A calibration standard ensures amplitude and phase stability in testing systems.
- "Null or Balance" refers to a condition in a device where no output is shown in a bridge circuit.
Key Principles and Effects
- The edge effect occurs when an eddy current signal is produced as the leading or trailing edge of a product approaches the test coil.
- Ferromagnetic shielding around AC coils decreases magnetic field extension and limits eddy current penetration.
- Eddy currents consistently travel in closed paths and cannot be induced in materials like paint.
Detection Limitations and Sensitivity
- Small inclusions in the center of a test rod are difficult to detect using encircling coils.
- The system should be nulled or balanced by comparing a reference standard with an acceptable test specimen.
- Eddy currents are most easily detected when they are perpendicular to the main dimension of any discontinuity.
Discontinuities and Sensitivity Analysis
- Eddy current systems are less sensitive to discontinuities that are aligned with the flow of eddy currents.
- Artificial discontinuities are machined into reference standards for reproducible quality levels.
- Increased test frequency reduces the effect of material thickness on conductivity readings.
Coil Design and Function
- A coil is defined as a conductor that produces an axial magnetic field when current passes through it.
- Impedance measures a test coil's opposition to the flow of alternating current.
- Absolute coil arrangements do not compare the test specimen with a reference or another section.
Application and Limitations
- Non-destructive tests do not aim to assure large volumes of material are available for sale.
- Reference standards primarily ensure accuracy and consistency, not instrument control settings for test specimens.
- Eddy current testing is not used for determining the exact chemistry of alloy materials.
Frequency and Material Response
- A frequency of 300 kHz provides the greatest eddy current penetration in aluminum.
- Test variables, such as probe speed changes, do not alter coil impedance.
- Permeability is represented by the symbol µ, an important property in testing.
Miscellaneous
- Calibration checks the accuracy and performance of instruments against standards.
- Eddy current testing relies on an alternating magnetic field to induce currents in conductive materials.
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Test your knowledge with these flashcards focused on Eddy Current Testing in Non-Destructive Testing (NDT). Each card presents terms and definitions essential for understanding the core concepts and applications of NDT techniques. Perfect for students and professionals looking to reinforce their learning.
