ET definitions

Question 1

Eddy Current (ET)

Answer 1

An electromagnetic NDT method that detects surface and near-surface discontinuities in electrically conductive materials by monitoring changes in coil impedance.

Question 2

Eddy Currents

Answer 2

Circulating electrical currents induced in a conductive material by an alternating magnetic field.

Question 3

Impedance

Answer 3

The total opposition to alternating current in a coil, consisting of resistance and reactance.

Question 4

Impedance Plane

Answer 4

A graphical X-Y display showing changes in resistance (X-axis) and reactance (Y-axis) of the probe coil.

Question 5

Lift-Off

Answer 5

The distance between the probe and the test surface; changes cause signal variations unrelated to defects.

Question 6

Skin Effect

Answer 6

The tendency of eddy currents to concentrate near the surface of a conductor, limiting penetration depth.

Question 7

Penetration Depth

Answer 7

The effective depth at which eddy currents flow, controlled by frequency, conductivity, and magnetic permeability.

Question 8

Frequency

Answer 8

The rate of alternating current in the probe; higher frequency reduces penetration depth.

Question 9

Conductivity

Answer 9

A material’s ability to conduct electrical current; affects eddy current strength and signal response.

Question 10

Magnetic Permeability

Answer 10

A material’s ability to support magnetic fields; dominant factor in ferromagnetic materials.

Question 11

Reference Standard

Answer 11

A test piece with known features used to calibrate the ET system and interpret signals.

Question 12

Phase Angle

Answer 12

The angular relationship of a signal on the impedance plane used to separate flaw signals from noise.

Question 13

Probe

Answer 13

The coil assembly that induces eddy currents and detects impedance changes.