Flexural wave sidewall sensor for noninvasive measurement of discrete liquid levels in large storage tanks

When large unattended tanks are filled automatically, there is a risk of overfilling. There exist many technologies for sensing liquid level and alarming when that level is too high, but very few of these are noninvasive. Options are further limited by the rippled surface during a fill, inaccessible bottom, floating roofs in many cases, and diameters often too large to be interrogated in pulse-echo or even in through-transmission mode, given an accuracy requirement of ±25 mm. The previously-available sidewall approaches for detecting liquid level based on ultrasonic attenuation were rejected because of coupling variability, sensitivity to internal residue or the wiper seals of floating roofs, or difficulty of verification for all liquid levels. These problems are avoided in the present work by using flexural waves