Abstract: To provide rapid level measurements with improved reliability, the present invention provides an apparatus and method for optically determining the level of a material through a technique for measuring the ratio of digital signals acumulated during an index interval and for modifying those signals to compensate for variations that can be caused by the shape of the beam detector signal. More particularly, the present invention provides a level detector system which includes a laser beam source which directs light to be reflected from a surface to be measured, the reflected light being directed to a stationary parabolic mirror.

Abstract: Level detection apparatus for determining the depth of a variable surface with respect to the apparatus is disclosed. The device includes a scanning source which causes an intense, collimated beam of light to move across the surface to be detected. First and second spaced detectors sensitive to light reflected from the surface are located at opposite sides of the scanning source and lie in the plane of the scanned beam so that the source directs light from the reflecting surface onto first one and then the other of the detectors. A circuit responsive to the receipt of the reflected beams by the first and second detectors produces first and second signals which will be spaced in time in accordance with the depth of the surface to be measured.

Abstract: An optical gauge having a laser or other such light source, the beam from which is cyclically directed upon a photo-detector by a rotating plane mirror, the time at which or during which in each revolution of the plane mirror the beam impinges upon the photo-detector being commensurate with a linear parameter of a workpiece upon which the beam is also directed, either constantly, as in the first disclosed embodiment, or cyclically as the beam is moved across the workpiece and occluded thereby during a portion of each rotation of the mirror, as in the second disclosed embodiment. The point on the rotating mirror at which the beam is reflected lies at the focal point of a fixed, parabolic mirror.