Annulus measuring device

A measuring device for measuring, at a plurality of circumferentially spaced locations, the radial thickness of an annulus defined by the curved outer wall surface of a first generally cylindrical, tubular-shaped member which has its axis positioned vertically, and the curved inner wall surface of a second generally cylindrical, tubular-shaped member which is generally concentrically located outside said first tubular-shaped member, said measuring device having an elongated body portion which has means on at least one end thereof which is adapted to be engaged by a flexible lowering and lifting means so that said measuring device may be lowered freely under its own weight or raised within said annulus so as to measure the radial thickness of said annulus at any point along its length or around its circumference, said elongated body portion having at least two axially spaced-apart sets of guide means extending from a first surface thereof which are adapted to guide said body portion for vertical movement relative to one of said curved outer and inner wall surfaces and parallel to the axes of said first and second tubular-shaped members, each of said at least two axially spaced-apart sets of guide means having a pair of transversely spaced contact surfaces shaped and positioned so as to be tangential to the said one of said curved outer and inner wall surfaces, said elongated body portion further having at least one contact portion which extends from a second surface of said body portion which is opposed to said first surface, said at least one contact portion being adapted to engage the other of said outer and inner wall surfaces, means for resiliently biasing apart said at least one contact portion and said at least two axially spaced-apart sets of guide means relative to each other with sufficient force to simultaneously engage both of the curved outer and inner wall surfaces which define the annulus, but with insufficient force to allow the said at least two axially spaced-apart sets of guide means to engage and track the wall surface with which they are in contact so as to cause movement in a non-vertical direction which would overcome the vertical gravitational force produced by the weight of the measuring device, means on said elongated body portion for generating and directing a pair of sensing beams in opposed coaxial directions outwardly relative to said first and second surfaces of said body portion and into contact with said inner and outer wall surfaces in a direction normal thereto, said two axially spaced-apart sets of guide means serving to maintain a predetermined angular position of said measuring device relative to said curved outer and inner wall surfaces and thereby causing said pair of sensing beams to be directed toward said curved outer and inner wall surfaces in a direction normal thereto, and means to sense the time it takes for said pair of sensing beams to contact said outer and inner wall surfaces and to be reflected back to their source whereby the radial thickness of said annulus may be calculated.