NDTnet 1998 Aug, Vol.3 No.8

Abstract

Fig.

Special probe geometries and combinations of different types of magnetic field sensors make an important contribution to the further improvement of the eddy-current testing method and results in new applications.
The paper compares several high resolution magnetic field sensors in applications on non-destructive testing. Differentmeasurement and evaluation methods at various open andcoverd faults in well electric conductive materials has been tested. Parameters of the comparison are the lateral and vertical local resolution and the signal-to-noise-characteristic. These tests aim at the 3D data acquisition of flaws.
All tested methods measure two independent parameters for several frequencies at the same place. The probes scan the surface of the material. Two one another independent parameters allows a 2D-indication of materials flaws. A 3D-location is possibility by using several frequencies at one place. Due to the correspondence between frequency and skin depth it is possible to get an information from the depth.At first an Impedance Analyzer measures the complex reactance of suitable eddy-current probes in interaction to materials.
The second method uses eddy-current probes in a new measurement method. The eddy current sensor is part of a relaxation circuit. In excitated state there is a damped electromagnetic oscillation. An electrical conductive material near the sensor causes a changing of the damping. The voltage drop of the probe is measured, rectified, amplified, integrated and delivers one signal. The other signal comes from measurement of duration of the first signal period.
The sensor of a third method is a Hall-effect device situated in a magnetic field of several multidifferential arranged exciting coils. The Hall-sensor permits the directe measurement of the magnetic field intensity at the material surface.
The paper presents and discusses the results of measurements and comparison of several magnetic field sensors and measurement methods for 3D-data acquisition. It makes a contribution to the use of different kinds of sensors and their combination in eddy-current testing. Sensor combinations increase the content of information of measured datas and insure the separation of flaws in materials.

Abstract Source:
Book of Abstracts, 7th European Conference on Non-Destructive Testing, 26-29 May 1998, ISBN: 87-986898-0-00

Full-Text Source:
Proceedings of the 7th European Conference on Non-Destructive Testing, 26-29 May 1998, ISBN:

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