Liquid-surface-level sensing based on transverse pulse train technique

A novel technique of liquid-surface-level sensing using a transverse pulse train is reported. Liquid level was detected by the reflection time of pulse train propagation on vertical, straight hollow wire partially immersed in liquid using two kinds of reflections. One is the echo from the liquid surface and the other is from the end of the sensing wire in which propagation speed is influenced by the liquid. Both the signals can be detected in a single measurement. In this paper, the standard deviation of the interface echo method and the end echo method is 26 and 199 μm, respectively. To the best of our knowledge, the error of the interface echo method is the lowest among all acoustic-based liquid-surface-level sensors in the current market. The attenuation coefficient of the interface echo method and the end echo method in water is 0.19 and 3.77 dB/m, respectively. The combination of the end echo and the interface echo techniques and low attenuation make it suitable for long distance and highly accurate liquid-surface-level sensing.