ECA Topologies

What is ECA?

Eddy Current Array is a non-destructive inspection method in which multiple eddy current coils are placed in a single housing. Some of these coils induce an electromagnetic field into a material. This field produce eddy currents that flow into the material. The other coils are then used to receive and analyze the eddy currents.

This technique represents an improvement overconventional eddy current inspection because it allows for the coverage of a large area in a single pass. Additionally, it makes the examination recordable, repeatable, less operator-dependent, and less time-consuming. Furthermore, it provides clear 2D/3D images of the part being tested.

Benefits of ECA

• Rapid, repeatable inspections
• Recordable, traceable data
• Intuitive C-Scan and 3D imaging
• Larger coverage, increased resolution

Absolute

• All channels equally sensitive
• Channels sensitives to defects in all orientations
• Very sensitive to liftoff variations
• Sensitive to thermal drifting
• Absolute response
• ½ channel overlap

Differential

• Channels not equally sensitive
• 60° orientation difference between even and odd
• Channels sensitives to defects in most orientations
• Insensitive to liftoff variations
• Insensitive to thermal drifting
• Differential response
• ½ channel overlap

Short Single Driver

• 2 sets of data are created with different sensitivities (axial & transverse)
• Sensitive to liftoff variations
• Sensitive to near surface defects
• Insensitive to thermal drifting
• Absolute response
• No channel overlap or ½ channel overlap possible configurations
• Short double driver configuration possible by multiplexing sequence

Long Single Driver

• 2 sets of data are created with different sensitivities (axial & transverse)
• 30° orientation difference between even and odd axial channels
• Creates slight sensitivity differences
• Less sensitive to liftoff variations than Short Driver topologies
• Sensitive to near-surface defects & slightly subsurface defects
• Insensitive to thermal drift
• Absolute response
• ½ channel overlap in the axial direction, increasing resolution

ECA imaging

By means of a multiplexing sequence and physical scanning (manual or encoded), plan views like C-scans and 3D representations are possible to generate a complete visualization of the inspected area and a better understanding of the detected indications.

Positioning and sizing estimations are possible directly on the image with the aid of dedicated cursors.

Here are some examples below using EMMA software.

Figure 1. C-scan view obtained from a carbon steel weld inspection allowing length estimation of crack-like indications

Figure 2. C-scan and 3D surface representation of a carbon steel plate allowing depth estimation of indications