SYSTEM AND APPARATUS FOR SAMPLING DETECTION SIGNAL OF SURFACE PLATE DEFECT

摘要

PURPOSE:To select and output a data of max. value in each cell by obtaining a defect detection signal of a face plate scanned by a scan line with circular arcs linked gradually at a fixed pitch. CONSTITUTION:A laser spot 1 herein used is oval with the long-axis radius sized DELTAr and a face plate 2 is divided into P areas of equal angle phicircumferentially and moves along the radius of the face plate 2 by one-Pth of DELTAr starting at the rotation center 0 of the face plate 2 each time it turns by an angle phi so that circular arcs are linked gradually at a pitch of DELTAr per turn. With this scanning, a measuring signal of an analog value continued as obtained by a defect detecting section is sampled by a sampling pulse (s). Then, each of the circular arcs by this scanning is divided by the length DELTAl, almost equal to the radius DELTAr of the spot 1 while being integer (n) times as much as a distance interval DELTAs of a pulse (s), to make cells. Max. value in the measurement data obtained by sampling for each cell is compared and selected to be outputted.