Linear angle measurement using continuous wave ultrasonic oscillator

We investigated the possibility of linear angle measurement of a vessel using a pair of partially submerged ultrasound transducers mounted on its walls. Measurements of the transfer function at different tilts of the vessel showed noticeable changes both in magnitude and phase responses. These changes were found easiest to track from the output frequency of an oscillator formed by using the transducers in a positive feedback loop. The output frequency depended on the tilt parabolically and its relative scatter was found lower compared to that of the angular output of an industrial accelerometer. The achieved output frequency capture rate of 150 measurements per second enabled meaningful tracking of dynamic changes of the test rig tilt in real time.