Patent ID: 7489129

Claim:
A method for detecting surface defects on a metal product as it is being continuously cast, using an eddy current sensor of the separate transmitter/receiver type having rows of contiguous aligned measurement cells that are separately controllable by multiplexing, the product to be inspected undergoing a traveling movement relative to the sensor, wherein, said sensor comprising a matrix of measurement cells distributed in rows and columns, and said matrix having at least first and second parallel rows of at least three measurement cells each, the multiplexing is activated in successive control steps in such a way that: in a given control step, first and second cells in each row are activated, these cells being separated from each other by at least one inactive measurement cell, the first cell being activated so as to generate eddy currents on the surface of said metal product and the second being activated so that it detects the eddy currents generated by the first cell, the flow of the eddy currents on the surface being modified by the presence of surface defects, and, at predetermined time intervals, the two activated cells are inactivated and said control step is repeated with two following cells, which are offset by at least one cell along the same row relative to the two inactivated cells, and so on, until the surface region to be inspected has been checked; and wherein said control step is carried out simultaneously for the first and second rows of cells, said first cells of each row belonging to just one column and said second cells of each row also belonging to just another column, said second cells of each row being configured so as to produce signals of opposite polarity when a defect is detected.