Location

San Diego, CA

Start Date

1-1-1985 12:00 AM

Description

Calibration of eddy current measurement systems is an important factor for attaining the accuracy and precision of measurement that quantitative nondestructive evaluation requires. The quantity of interest in most forms of eddy current inspection is △Z, the change in probe impedance induced by a flaw. Flaw signals produced by surface-breaking cracks are small; typical flaw signals for an air core probe amount to a few tenths of one percent of the probe’s impedance in air. Such small signals are easily obscured by the impedance changes caused by small variations in the height of the probe above the workpiece (lift-off). To discriminate against lift-off, conventional eddy current instruments determine the phase of △Z relative to lift-off and the magnitude of the component of △Z in quadrature with lift-off. But this information is not sufficient to perform flaw signal inversion; rather, the absolute magnitude and phase of △Z are necessary. Thus, quantitative inversion of eddy current signals to obtain flaw sizes requires methods for calibrating eddy current measurement systems

Book Title

Review of Progress in Quantitative Nondestructive Evaluation

Volume

4A

Chapter

Chapter 2: Eddy Currents

Section

Probes and Instruments

Pages

411-420

DOI

10.1007/978-1-4615-9421-5_46

Language

en

File Format

Application/pdf

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Jan 1st, 12:00 AM

Calibration Methods for Eddy Current Measurement Systems

San Diego, CA

Calibration of eddy current measurement systems is an important factor for attaining the accuracy and precision of measurement that quantitative nondestructive evaluation requires. The quantity of interest in most forms of eddy current inspection is △Z, the change in probe impedance induced by a flaw. Flaw signals produced by surface-breaking cracks are small; typical flaw signals for an air core probe amount to a few tenths of one percent of the probe’s impedance in air. Such small signals are easily obscured by the impedance changes caused by small variations in the height of the probe above the workpiece (lift-off). To discriminate against lift-off, conventional eddy current instruments determine the phase of △Z relative to lift-off and the magnitude of the component of △Z in quadrature with lift-off. But this information is not sufficient to perform flaw signal inversion; rather, the absolute magnitude and phase of △Z are necessary. Thus, quantitative inversion of eddy current signals to obtain flaw sizes requires methods for calibrating eddy current measurement systems