| 摘要 |
Measurement of lengths for determining the out- side diameter, wall thickness or inside diameter of tubes, specifically tubes of zircaloy alloy for use as cladding for nuclear fuel. The tubes must be maintained to close tolerances. The measurement is carried out with a laser micrometer which generates a planar laser beam. A mandrel of tungsten carbide having a coaxial projection is posi- tioned so that its transverse dimension intersects the beam and is parallel to the plane of the beam. A first length is measured between the end of the beam and the nearest point on the projection. A tube is mounted on the projec- tion with its longitudinal axis parallel to the longitudinal axis of the mandrel and its inner surface engaging this nearest point. A second length is measured from the end of the beam and the nearest point on the tube. The outside diameter is measured as a third length on the shadow of the tube produced by the laser between the shadow of the near- est point and the shadow of the most remote point from the end of the laser beam. The wall thickness is equal to the first length less the second length. The inside diameter 1s the outside diameter less twice the wall thickness. The width of the projection is only slightly greater than the width of the laser beam so that the tube is positioned, asnearly as practica ble, on a knife edge. Each measurement of a length is the means of a plurality (typically eight) of measurements taken at eight, angularly and longitudinally, randomly displaced positions of a tube. Evaluation based on misleading deviations from the control limits, such as a burr or a speck of dust on a tube, are ruled out. An advantage of this invention is that the measurement is carried out with only one instrument. Prior-art practice requires the use of two instruments: one to measure the OD and the other the ID.
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