Portable eddy current NDT instrument using two different implementations.
ABSTRACT This paper describes two implementations towards the development of a portable low-cost system capable of detecting defects on metallic surfaces through non-destructive testing. The defect detection is made via an eddy-current probe using a giant magnetoresistor (GMR) sensor. Both approaches use a computer mouse as a position device to locate the probe and deliver a graphical representation to facilitate the defect analysis. One implementation is based on a planar excitation coil, embedded power supplies and the signal processing is made by a dsPIC. The dsPIC controls the signal generation, the measurement procedure and the communication. The defect visualisation can be made in a LCD in real-time or transmitted to a PC. The other implementation uses a low-cost analog system to reduce the data processing required to detect the surface defects. The controller is a PIC microcontroller that does all the analog/digital conversions and transmits the defect data to a PC via wireless channel.
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ABSTRACT: The Pulsed Eddy Current (PEC) technique is an effective method of quantifying defects in multi-layer structures. It is difficult to detect defects in riveted structures of aging aircraft. Based on theoretical analysis of PEC technique, three different probes, including a differential hall probe, a differential coil probe, and a two-stage differential coil probe are designed to detect this kind of defects. The averaging method and wavelet analysis method are used to de-noise the hall response signals. By selecting peak amplitude and zero-crossing time of response signal in time domain as key features, defects in riveted structures can be detected effectively. The experimental results indicated that the differential coil probe acted as effectively as the differential hall probe. The defects between third layer and fourth layer in riveted structures can be detected by utilizing the two-stage differential coil probe. The PEC technique has a promising application foreground in the field of aeronautical nondestructive testing.Ndt & E International - NDT E INT. 01/2010; 43(2):176-181.
Conference Proceeding: Inductive Probe for Flaw Detection in non-Magnetic Metallic Plates Using Eddy Currents[show abstract] [hide abstract]
ABSTRACT: This paper describes the design of an inductive sensor and its application to detect the presence of structural flaws inside electrically conducting nonmagnetic plates. The principle of operation is based on the measurement of the induced voltages in two sensing coils. These voltages are related to the eddy currents that are generated inside the plates with perturbations due to the electrical conductivity inhomogeneities. The modeling work aims at determining the optimum operating frequencies and the resulting signal magnitudes.Instrumentation and Measurement Technology Conference Proceedings, 2008. IMTC 2008. IEEE; 06/2008
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ABSTRACT: The purpose of this paper is to introduce a new eddy-current testing technique for surface or near-surface defect detection in nonmagnetic metals using giant magnetoresistive (GMR) sensors. It is shown that GMR-based eddy-current probes are able to accurately detect short surface-breaking cracks in conductive materials. The self-rectifying property of the GMR sensor used in this study leads to a simplified signal conditioning circuit, which can be fully integrated on a silicon chip with the GMR sensor. The ability to manufacture probes having small dimensions and high sensitivity (220 mV/mT) to low magnetic fields over a broad frequency range (from dc up to 1 MHz) enhances the spatial resolution of such an eddy-current testing probe. Experimental results obtained by scanning two different probes over a slotted aluminum specimen are presented. General performance characteristics are demonstrated by measurements of surface and subsurface defects of different sizes and geometries. Dependence of the sensor output on orientation, liftoff distance, and excitation intensity is also investigatedIEEE Transactions on Magnetics 10/2001; · 1.42 Impact Factor