ELECTRO-OPTICAL LEVEL APPARATUS

An electro-optical level employs a bubble tube with opposite first and second ends. First and second light emitters are disposed respectively beyond the first and second axial ends of the tube and direct light toward the ends of the bubble in the tube. Electro-optical detectors are aligned substantially parallel to the axis of the tube and are spaced from the tube. First and second beams from the respective first and second light emitters scatter as the beams impinge upon the bubble. However, the scattered light from each light emitter will form a bright spot on the respective electro-optical detector at a point corresponding to the end of the bubble. The locations of the bright spots are detected by the electro-optical detectors and precisely determine the locations of the opposite ends of the bubble regardless of dimensional changes of the tube or the bubble due to temperature variations.