A method for optoelectronic control of liquid volume in a tank

The article describes a method for optoelectronic control of liquid volume in a tank. Measurements can be performed remotely without tank calibration. The method is based on the fact that there is a near-wall region where the liquid surface has a higher reflectivity. This region occurs due to surface tension or minor ripples. With this method, first, an image of liquid surface is taken with a photo-camera. Then, a near-wall liquid-air boundary is identified in the image before calculating the current area of the liquid surface. When the tank is filled for the first time, the device records the liquid area for every level. A calibration table is automatically created without applying additional tools. To avoid the error caused by inaccurate photo-camera positioning, a special mathematical model is devised. It uses reference marks made on tank walls horizontally. An algorithm for recognition of liquid boundaries in the image is developed. Measurements of the liquid volume conducted using a laboratory prototype have shown the reduced error to be within 0.5%, provided that the digital photo-camera is not rigidly fixed.