US 5,525,903 AGranted

Eddy current method of acquiring the surface layer properties of a metallic target

AssigneeMicro-Epsilon Messtechnik GmbH & Co. KG

InventorsRoland Mandl, Axel Seikowsky, Andreas Spang

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Abstract

A sensor arrangement and a method of acquiring properties of the surface layer (3) of a metallic target (2), which allow a nondestructive and substantially distance-independent measurement to be performed, with the requirements to be met by the sensor positioning being minimal. The sensor arrangement (1) comprises a combination of at least one eddy-current sensor (5) with at least one displacement measuring sensor (6), the depth of penetration of the eddy currents generated by the eddy-current sensor (5) corresponding to at least twice the thickness of the surface layer (3), and the displacement measuring sensor (6) serving to determine the distance of the sensor arrangement (1) from the target surface (4). The measuring signals of the eddy-current sensor (5) and the displacement measuring sensor (6) are evaluated on the basis of a hypothetical depth of penetration of the eddy currents, which is to be determined as a function of the frequency of the eddy currents and of the conductivity and permeability of the base material (8) of target (2).

Claims13

Dependent claims

A method of acquiring properties of a surface layer (3) of a metallic target (2) which comprises a base material (8) and the surface layer (3), with the conductivity and permeability of the base material (8) and the surface layer (3) of the metallic target (2) being known, and comprising the steps of

estimating the thickness of the surface layer (3) to be tested,
positioning a sensor (1), which comprises at least one eddy current sensor (5) which is operable at a variable frequency and at least one displacement measuring sensor (6, 7) adjacent the target (2) so that the displacement measuring sensor (6) serves to determine the distance between the sensor (1) and the outer surface of the surface layer (3),
determining a frequency of the eddy current sensor (5), based upon the known conductivity and permeability of the base material (8) and the surface layer (3) and the estimated thickness of the surface layer (3), which under ideal conditions would cause the eddy current to penetrate to an expected depth which is at least equal to the estimated thickness of the surface layer (3),
operating the sensor (1) so that the eddy current sensor (5) operates at the determined frequency, and
evaluating any difference between the actual penetration of the eddy current sensor (5) as measured by the sensor (1) and the expected depth of penetration.

2 more elements

Dependencies are inferred from the claim text.