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70 Cards in this Set
- Front
- Back
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what are some of the advantages of Eddy current?
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fast, automated, no harm to part, no post cleaning, equip is light and portable, sensitive to small surface cracks, wide range of applications.
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Disadvantages of eddy current?
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applicable only to metal, Electrical and magnetic interference may cause problems, requires highly trainded personnel, and affected by numerous variables.
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What is the movement of electric current(electrons)?
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Current flow
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An electric field drives?
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Free electrons
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Within a wire electrons collide with the atoms making up the conductor, what does this collision do?
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slows them down and caused energy loss through heat.
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the collision of electrons and atoms also limits whats?
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Current flow
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What type of material losses large amounts of energy to heat?
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High resistivity materials.
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What type of material produces little heat?
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Low resistivity materials.
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What is the opposite of resistivity?
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conductivity
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Low conductivity equals?
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High resisistivity.
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low resistivity has?
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High conductivity.
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What is defined as magnetic field?
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When a traveling electron has a force act upon it in a sidways manner.
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Like an electric current a magnetic field can do what?
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exer a force on electrons producing current flow.
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in order for current to flow either the magnetic field or the conductor must?
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Move past each other.
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When a magnet is moved past a conductor what two thing happen?
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current is induced
An the current that is induced creates a secondary magnetic field. |
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What is lenz's law?
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States that when a magnet and a conduct move past each other current flow is induced and a secondary magnetic field is created.
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The magnetic field around a straight wire is week unless?
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Alot of current is pushed through it.
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By forming a wire into a coil what is the result?
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It produces a stronger magnetic field with far less current.
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As current builds from 0 to max what happens?
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lines of induction are geerated and move from the coil
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At max current the max number of lines of induction exist where?
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At the max distance from the coil.
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A coil resting on a surface of an electrical conductive material induce current flow where>
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Directly below the coil and weaker current ouside the coil dia.
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The total opposition to current flow in a coil?
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impedance
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opposes current flow by causing heating of the wire
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resistance.
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What is reactance?
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opposes changes in current flow by causing energy to be stored in the field around the wire.
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What are actually the two types of reactance?
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inductive, and capacitive.
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What is resistance?
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Opposes current flow by causing heating of the wire
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When voltage is applied the current?
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Starts and stops at exactly the same time as the voltage.
The voltage and current are said to be in phase. |
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When isolated from resistance is the opposition to the flow of AC current caused by?
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Inductance in a circuit current are 90 Degrees.
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Eddy current testing is accomplished by?
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observing changes in impedance of a coil of wire.
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Meter instruments measure the changes in?
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resistance and reactance in needle movement/
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A measure of ease with which electrons can flow through a material?
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Conductivity also the opposite of resistivity.
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Conductivity is based on what?
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IACS copper.
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Distribution and intensity of eddy currents in nonmagnetic parts are affected by?
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conductivity
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magnitude of eddy currents immediately below the surface is dependent on the?
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Conductivity of the part
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High conductivity equals?
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Strong eddy currents
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penetrating levels are stronger in?
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Poor conductive materials.
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Eddy current can be used to sort parts of different?
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conductivity
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the ease in which a part may be magnetized?
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permeability
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in ferromagnetic materials permeability rather than conductivity is the principle factor in determining what?
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eddy current response.
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ferromagnetic materials greatly increase the flux density of?
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eddy current coils field
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As the magnetic field of the coil comes in contact with the test part what happens?
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current flow is induced.
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the closer the coil is to the part the stronger what will be?
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The stronger the eddy currents.
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the further away from the part the weaker the eddy current field will be provided what happens?
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The magnetic field is still in contact with the part
This change in coupling is refered to as lift off. |
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the term describing the degree of magnetic coupling for both the inside diameter coil and outside diameter of a part.
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fill factor
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A fill factor of what gives a reasonably sensitivity and clearance?
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90%
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Variations in inspection part configuration can influence eddy current response is what?
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Geometry
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What factors affect eddy current impedance?
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Conductivity, Permeability, coil/magnetic coupling, Geometry, discontinuities, frequency and temperature
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What represent the number of cycles per second of A/C used to establish a magnetic field in a part?
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Frequency
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Higher frequency results in what?
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less penetration of eddy currents in the part
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What affects both electrical conductivity and magnetic properties of test part?
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Temperature
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What is the opposite of conductivity?
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Resistivity
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When is current and voltage said to be "in Phase"?
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When the voltage is applied, the current starts and stops at exactly the same time as the voltage.
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What are the two types of reactance?
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inductive and capacitive
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Eddy current testing is accomplished by what?
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Observing changes in impedance of a coil of wire
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The total opposition to current flow in a coil is what?
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Impedance
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What are the two factor of impedance?
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Resistance and Reactance
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What opposes current flow by causing heating of the wire?
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Resistance
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What opposes changes in current flow by causing energy to be stored in the field around the wire?
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Reactance
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Where is the highest density of eddy current flow?
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At the surface
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What is one standard depth of penetration?
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The depth at which the eddy current strength has dropped to approximately what 36.8% of it surface value
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What are the surface value of the two and three standards depth of penetration?
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14% for two and 5% for Three
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What three things does the actual depth of the 36.8% point depend on?
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Frequency, Conductivity of the part, and permeability of the part
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What are the two types of signal displays?
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Amplitude and impedance plane
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What is used to display signal amplitude only?
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Analog or digital meters
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What does the impedance plane measure?
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Amplitude and phase
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Amplitude and phase is also known as what
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reactance and resistance
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What is the impedance plane displayed on?
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a two dimensional cathode ray tube(CRT)or liquid crystal display(LCD) screen
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With current is flowing through the test coil and the coil positioned on a flaw free area, impedance can be adjusted so that zero current flows through the amplifier. This is known as what?
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Balancing and nulling the bridge
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What happens to the bridge when it encounters a flaw?
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It becomes unbalanced causing current to flow through the amplifier
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What five variables are displayed in the impedance diagram?
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Conductivity, thickness, permeability lift off and frequency
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