| 摘要 |
PROBLEM TO BE SOLVED: To accurate measure in a short time in a poor environment such as an ironworks where water, vapor, various kinds of smokes and dust scattering a peripheral part, or in constitution receiving a reflected light. SOLUTION: This measuring apparatus is equipped with an irradiation part 2S for scanning a steel pipe 3 whose center position is previously known with a light beam, a light receiving part 2R for receiving a light beam after the light beam has passed an existing position of the steel pipe 3, a comparing part 27 for comparing a cutoff starting point N1 and a cutoff ending point P1 when the light beam is cut off with a set value TH from the light receiving result by the light receiving part 2R and detecting the positions, and an outer diameter operating part 33 for operating the outer diameter D of the steel pipe 3 on the basis of a cutoff starting position and a cutoff ending position, which are the nearest to the position of the center of the steel pipe 3 out of the cutoff starting positions Ni and cutoff ending pints Pi which are detected by the comparison part 27.
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