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eddy current inspection


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what are some of the advantages of Eddy current?
fast, automated, no harm to part, no post cleaning, equip is light and portable, sensitive to small surface cracks, wide range of applications.
Disadvantages of eddy current?
applicable only to metal, Electrical and magnetic interference may cause problems, requires highly trainded personnel, and affected by numerous variables.
What is the movement of electric charge?
Current flow (electrons)
An electric field drives?
Free electrons
Within a wire electrons collide with the atoms making up the conductor, what does this collision do?
slows them down and caused energy loss through heat.
the collision of elctrons and atoms also limits whats?
Current flow
What type of material losses large amounts of energy to heat?
High resistivity materials.
What type of material produces little heat?
Low resistivity materials.
What is the opposite of resistivity?
Low conductivity equals?
High resisistivity.
low resistivity has?
High conductivity.
What is defined as magnetic field?
When a traveling electron has a force act upon it in a sidways manner.
Like an electric current a magnetic field can do what?
exer a force on electrons producing current flow.
in order for current to flow either the magnetic field or the conductor must?
Move past each other.
When a magnet is moved past a conductor what two thing happen?
current is induced

An the current that is induced creates a secondary magnetic field.
What is lenz's law?
States that when a magnet and a conduct move past each other current flow is induced and a secondary magnetic field is created.
The magnetic field around a straight wire is week unless?
Alot of current is pushed through it.
By forming a wire into a coil what is the result?
It produces a stronger magnetic field with far less current.
As current builds from 0-max what happens?
lines of induction are geerated and move from the coil
At max current the max number of lines of induction exist where?
At the max distance from the coil.
A coil resting on a surface of an electrical conductive material induce current flow where>
Directly below the coil and weaker current ouside the coil dia.
the total opposition to current flow ina coil?
opposes current flow by causing impedance of the wire
What is reactance?
p[ses chamges in current flow by causing energy to ve strored in the field around the wire.
What are actually the two types of reactance?
inductive, and compasititve.
What is resistance?
When isolated from reactance is the ratio of and applied voltage to current flowing through a circuit.
When coltage is applied the current?
Startes and stops at exactly the same time as the voltage.

The voltage and current are said to be in phase.
=Whgen isolated from resistance is the opposition to the flow of AC current caused by?
Inductance in a circuit current lage 90 Degrees.
Eddy current testing is accomplished by?
oberving changes in impedance of a coil of wire.
Meter insutruments messure the changes in?
resistance and reactance in neddle movement/
A measure of ease with which electrons can flow through a material?
Conductivity also the opposite of resistivity.
Conductivity is based on what?
IACS copper.
Distribution and intensity of eddy currents in nonmagnetic parts are affected by?
magnitude of eddy currents imediatly below the surface is dependent on the?
Conductivity of the part
High conductivity equals?
Strong eddy currents
penetrating levels are stronger in?
Poor conductive materials.
Eddy current can be used to sort parts of different?
the ease in which a part may be magnetized?
in ferromagnetic materials permeablilty rather than conductivity is the principle factor in determining what?
eddy current response.
ferromagnetic materials gretly increase the flux density of?
eddy current coils field
As the magnetic field of the coil comes in contact with the test part what happens?
current flow is induced.
the closer the coil is to the part the stronger what will be?
The stronger the eddy currents.
the futher away from the part the weaker the eddy current field will be provieded what happens?
The magnetic field is still in contact with the part

This change in coupling is refered to as lift off.
the term describling the degree of magnetic coupling for both the inside ddiameter coil and ousided diameter of a part.
fill factor
A fill factor of what gives a reasonably sensitivity and clearance?

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