Image-based height measuring systems for liquid or particles in tanks

In this paper, an image-based height measuring system for liquid or particulate material, which does not use pixels to measure distance, is proposed to measure the material height inside of a storage tank. Two laser projectors, fixed on a base, define a vertical plane to produce two projected bright spots on the surface of the material in the tank. A timer, instead of pixel counter, for measuring distance and a circuit for counting the number of clock pulses between the two bright spots are employed to calculate the distance between the two projected bright spots in the video images. Since the two laser projectors form an isosceles triangle, there is a simple relationship between the actual measured height and the distance of the two bright spots. The actual height of liquid in the tank can be calculated from a simple formula. One does not have to use a expensive high speed DSP microprocessor to identify the bright spots, but just use a simple voltage comparator to identify them. Experimental results have demonstrated the effectiveness of the proposed system.