Electricity: measuring and testing – Magnetic – With compensation for test variable
Patent
1980-09-30
1983-05-10
Strecker, Gerard R.
Electricity: measuring and testing
Magnetic
With compensation for test variable
324240, G01N 2790, G01R 3312
Patent
active
043832180
ABSTRACT:
Disclosed is an eddy current inspection system for nondestructive detection of subsurface flaws in regions of multilayer conductive structure that surround a fastener which joins the conductive layers. The eddy currents are induced by an aperiodic drive current having a relatively long rise time and a relatively last fall time that is supplied to a drive coil and a pick-up coil that is mounted with the drive coil supplies a signal representative of the induced eddy currents. Compensation is provided for variation in lift-off (spacing between the surface of the structure being inspected and the surface of the drive coil and pick-up) by utilizing parametric relationships relative to the maximum amplitude of inspection signals supplied when subsurface flaws exist and inspection signals supplied when lift-off is present. Because similar parametric relationships exist relative to other system characteristics that affect the electromagnetic environment of the inspection media, compensation can also be provided for variation in the height of fasteners (protrusion), fastener edge margin, and gaps or spacing between the successive conductive layers of the multilayer structure. By utilizing a microprocessor or other sequential digital signal processing apparatus, values that define the parametric relationships utilized in compensating for any particular system characteristic can be stored in memory for the inspection of a relatively large number of structural configurations.
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Calibration of Eddy Current Systems with Simulated Signals, J. C. Crowe, 9/77-Materials Evaluation, pp. 59-64.
Hansen Karl A.
Hendrickson Iver G.
Strecker Gerard R.
The Boeing Company
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