Quantifying the Relative Thickness of Conductive Ferromagnetic Materials Using Detector Coil-Based Pulsed Eddy Current Sensors

Pulsed eddy current sensing is an electro-magnetic sensing technique used to assess certain physical properties and effects of electrically conductive and sometimes ferromagnetic materials. We will introduce the use of a software interface of utilizing the pulsed eddy current signals captured from detector coil based sensor architecture and how to extract information from those signals. This protocol enables a relative thickness quantification of ferromagnetic metallic woolite structures using pulsed eddy current sensing.

This technique enables the measurement of the extent of corrosion, graphitization or wool loss of ferromagnetic wool like structures for assessment of there structure and build and integrate it. For pulsed eddy current signal processor installation, locate and execute the PEC signal processor. exe file, and when the interface appears, click next.

When the next interface opens, specify the file location for installation and check the add a shortcut to the desktop check box to add the software icon to the desktop. Click next and specify the installation location for the required run time environment. When the installation is complete, click finish.

The desktop icon will appear. Before beginning the analysis, use a detector coil based pulsed eddy current sensing unit with an operating electronic box and a detector coil based sensor to collect pulsed eddy current signals from the metal structure of interest. At the end of the scan, export the collected signals from the sensing unit to a compatible, editable word processor and confirm that the signals are arranged as a table.

Copy the table to the desktop and double click the desktop icon to run the application. The interface will open. To load the signals, click the load signals tab and select the file containing the signals to import the signals to the software interface.

When the number of signals contained within the table containing raw signals appears, click pot signals, and observe the signals plotted in logarithmic scale. Click the zoom tab and adjust the plot window for the linear region until it is clearly visible. The lower and upper margins should encompass a straight line region within the light shade of the signals.

If unsure, we recommend generating relative thickness values using several margins and then compare the results. After entering reasonable lower and upper margins for the region, click plot margins and wait for the margins to be plotted in green. Click extract features, the straight line segments will be plotted in red.

Click calculate relative thickness to observe the plotting of a histogram of calculated relative thickness values. Click save relative thickness to save the calculated relative thickness values. Enter a file name, and click ok.

Then click ok again to confirm the file name. The relative thickness values will be saved as a table on the desktop. The relative thickness values shown on screen are in the form of fractions.

One denotes maximum thickness for the 100%reference. Here, the typical shape of a time domain signal expressed in the logarithmic form captured from a detector coil based pulsed eddy current sensor is shown. An indicative linear region of the later stage of the logarithmic signal can be observed, for which t is much greater than 0, and from which the decay rate feature beta is extracted.

Here, a set of signals captured on different thicknesses of gray cast iron is shown. This signal corresponds to the maximum thickness with the maximum beta value in the set. Such values can be selected as reference beta values to facilitate quantification of the relative thickness, using the equation as indicated.

In this table, the actual relative thickness values and the relative thickness values calculated from beta values obtained from pulsed eddy current signals for a representative experiment, are shown. Here, the corelation between pulsed eddy current signal based relative thickness estimates and the actual relative thickness values can be observed. The effectiveness of the method is demonstrated by the high correlation depicted by the linear relationship.

Take care to avoid the current region of the pulsed eddy current signal and to select the linear region at the light stage to allow extraction of the beta feature. Pulsed and other eddy current techniques are commonly used for a anomaly detection, physical property measurements, and for the assessment of non-metallic coatings covering metallic structures.