Optical measurement of vane ring throat area

A device for optically measuring throat area in a vane ring for a gas turbine engine, the vane ring having an annular array of vanes defining a plurality of individual throats between adjacent leading and following vanes of the array, each said individual throat being a planar opening with a periphery bounded in a radial direction by an inner vane shroud and an outer vane shroud and bounded in a circumferential direction by a trailing edge of the leading vane and a projected co-planar line on a convex surface of the adjacent following vane,

• the device comprising:
• fixture means for holding the vane ring in an imaging position wherein the periphery of a selected individual throat is within an optical measuring field of view;
• a primary radiation source disposed in a throat defining position wherein an area of shadow is cast by said primary radiation source on the vane ring initiating in the plane of the selected throat, said area of shadow being surrounded by an area of reflectance;
• radiation detector means for capturing an image of a portion of the vane ring within the field of view;
• and
• image analyzing means for analyzing the image to acquire a dimensional data of a dark portion of the image proportional to an individual throat area of the selected throat.