Probe Conditions Affecting Eddy Current Flow (4)

Question 1

List the probe conditions that can impact EC flow:

Answer 1

• Frequency Selection
• amount of circuit current
• coil windings
• lift off
• material diameter to OD & ID diameters (fill factor)
• edge effect & end effect
• probe “wobble”

Question 2

Frequency and diameters role on inspection

Answer 2

lower frequency + large diameter coils = deeper inspection

Question 3

Frequency Selection

Answer 3

Higher frequency = greater skin effect and higher EC strength and concentration at surface

Lower frequency = increase depth of penetration and increase sensitivity for sub surface inspections

Question 4

Amount of Circuit Current

Answer 4

Increasing amperage of primary current flow =

• increase in inductance/flux density
• increase EC strength + depth of penetration
• current flow limited to what circuitry can handle!

Question 5

Coil Windings

Answer 5

• type of windings
• number of windings
• diameter
• cores
• shielded vs. non-shielded
• conductivity

Increasing # windings, increase coil diameter, soft core etc. will increase EC strength and depth of penetration

Question 6

Fill Factor

Answer 6

(spacing between ID bobbin probes and OD encircling probes in relation to tube walls or rod surfaces)

• Ideally ratio should be no less than 80% (0.8)
• fill factor = diameter of part/inside diameter of coil

Question 7

Edge & End Effect

Answer 7

EC will be greatly distorted when flow is interrupted by the edge of a part of end of a tube.
signals at the edge or end can be interrupted due to noise.

Question 8

Probe “Wobble”

Answer 8

Result of a rough scanning surface/poor probe handling.

causes operating point on the signal display to be erratic.