A Novel Conductivity Classification Technique for Non-Magnetic Tilting Metals by Eddy Current Sensors

Abstract

The classification of conductivity is significant for recycling metallic scraps. The eddy current sensor is distinct from other classification methods by its merits of non-contact, economical setup , fast measuring, and so forth. By introducing a setup that could ensure the single-valued mutual inductance trajectory on the complex plane, we propose the circle fitting method to extract the global features of different trajectories. It is subsequently observed that the fitting circle centers-one of the global featuresfor the same conductivity with various tilting angles are distributed longitudinally close to each other. The feature line, which is parallel to the abscissa axis, is introduced to represent this gathering distribution behavior. The feature lines for different conductivity are distinguishable. Thus, we construct a simple classification method with only two steps. The test results show great fidelity of the proposed classification technique which can successfully classify the tilting metallic samples within 11.3 • .

Sloping-Invariance for Nonferrous Metallic Slabs at Multiple Frequencies by Eddy Current Sensors

“…By conducting the seven-step classification process in Section IV, the intercepts for the non-sloping samples at frequencies from 40 kHz to 100 kHz constitute the classification criterion, and the classification rates within 14.0 • at these frequencies are 100%, 100%, 96%, and 100%, respectively. Our classification method by resorting to this sloping-invariance is more accurate compared to the classification rates in [15], [16], which are 95% within 9.0 • and 96.7% within 14.0 • at 40 kHz, respectively. Overall, the sloping-invariance is broadband and appropriate for the conductivity classification.…”

“…The experimental results of mutual inductance are depicted in Fig. 5, where the curve is rotating clockwise when the conductivity is increasing, the same as in [15], [16], [29]. By transforming the measured mutual inductance in the form of phase and normalized magnitude, it is shown in Fig.…”

“…There are some reported works recently [15], [16] that manage to classify sloping metallic samples. Two different classification schemes are presented, which are moving the sample (resulting in multi-valued mutual inductance curves) and moving the sensors (resulting in single-valued mutual inductance curves).…”

“…Nonetheless, the slopinginvariance found in this work from non-sloping samples can be directly utilized as the criterion to classify sloping samples. Moreover, the classifiable tilting angle is restricted within 9.0 • in [15], and the operating frequency in [16] is 40 kHz, which is one of the frequencies used in this work.…”

Linear Characteristics of the Differences in Phase Tangents of Triple-Coil Electromagnetic Sensors and Their Application in Nonmagnetic Metal Classification

“…Du et al achieved the classification of tilted metals by fitting a linear relationship between the tilt angle and phase using the phase of inductance change as a feature combined with the tilt angle obtained from the photoelectric sensor [ 21 ]. Then, they proposed a circle-fitting method to extract the global characteristics of different mutual metal inductance trajectories on the complex plane, so that metals with larger tilt angles could also be accurately classified [ 22 ]; a pseudo-linear relationship between the magnitude–phase curve of inductance change was also found [ 23 ]. Liu et al extracted the characteristic slope from the normalized inductance trajectory on a complex plane and used the least squares method to classify metals with a larger tilt angle [ 24 ].…”