JPS6439507A - Method and device for measuring diameter of transparent columnar body - Google Patents

Abstract

PURPOSE:To measure the external diameter and internal diameter of a body to be measured at the same by making a light beam incident on the side face of the body to be measured while dipping the body to be measured in liquid whose refractive index is closed to that of the external layer of the body to be measured, and detecting the quantity of transmitted light. CONSTITUTION:An optical fiber 1 as the body to be measured is stored in a cell 2, a laser 10 is deflected by a scanner 12 to scan the cell 2 in a direction S in a reciprocal sine shape, and a signal processing circuit 5 samples a light receiving signal to measure the coordinates of a light quantity change point. Here, when the refractive index of the liquid put in the cell 2 is close to the refractive index of the clad, a light beam incident on the border between the liquid and clad upper end travels straight, but the level of the transmitted light is extremely low below it. Further, a little light passing nearby in the core closely to the border is transmitted, but the quantity of transmitted light increases toward the center of the core. For the purpose, the quantity of transmitted light is binarized by using a specific threshold value and the required time from a reference point to each change point of the binarization data is found and converted into distance data to computes the external diameter, core diameter, etc.