GAP MEASURING INSTRUMENT FOR ROTARY MACHINE

PURPOSE:To measure a gap length with an extremely high accuracy and also without an error, by detecting a gap length of a seal fin part, based on a magnified projected image of a rod-shaped member, which has been reflected on a screen by a light source. CONSTITUTION:A magnified projected image 14 of a lead wire 10 is reflected on a screen 13 by a diffused light emitted from a point light source 12. In the center part of the screen 13, a scale 15 is provided along its upper and lower directions. The lead wire 10 or the point light source 12 consists of a structure by which its position can be adjusted in the right and left, and the upper and lower directions so that an image of a part of its edge groove 11 is just positioned in the part of the scale 15. When a distance between the point light source 12 and the lead wire 10, and a distance between the point light source 12 and the screen 13 are denoted as L1, and L2, respectively, depth of the edge groove 11 of the lead wire 10 is magnified to L2/L1 times on the screen 13. Accordingly, by reading the thickness of the remaining part of the edge groove part of the magnified projected image 14 by the scale 15 provided on the screen 13, a gap length of a seal fin part can be measured with a measuring accuracy of L2/L1 times.