| 摘要 |
PURPOSE:To carry out positioning of an inspected body for the center axis of visibility range easily and surely by forming at least one optical path in the vicinity of the visibility range limit on a measurement slice surface and detecting the shield of the optical path by an inspected body. CONSTITUTION:A plurality of reflection bodies 12 are arranged along a spiral supposed line on the inner peripheral surface of a hall 10 for measurement, and laser beams are inputted, keeping a certain angle from outside into a reflection body 12 at the right edge of the hall 10 through an optical fiber 20 from a laser oscillator 18, and the laser beams are reflected in succession in multiangular spiral form, and the hall 10 is constituted so that an optical path 16 irradiating from the left edge is formed. The reflection light supplied from the reflection body 12 at the terminal of the optical path 16 is received by a light detector 22 arranged outside at the left edge of the hall 10, and an output is outputted into a display means 24 such as alarm lamp, etc., by the light detector 22, and the fact if the light path 16 is shielded or not is displayed. Accordingly, an inspected body is adjusted so as not to come out of visibility range in the hall for measurement, capable of being easily positioned.
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