Development of Ultrasonic Long Waveguide Level Sensor Using Different Wave Modes

This paper reports a long ultrasonic waveguide based sensor to monitor the fluid level utilizing different modes. The longitudinal L(0,1), torsional T(0,1), and flexural F(1,1) wave modes were transmitted and received simultaneously in the stainless steel wire waveguide utilizing a shear transducer with a 45º orientation of the waveguide axis. A long waveguide (> 10 m) can reach more depths and a wider region of interest, and several sensors (reflectors) can be provided along the length of the waveguide. Long waveguides have a significant role in the hostile environment for the process industries to monitor the fluid level and material properties. The concept of level measurement is with respect to measuring the attenuations and reflection factors of the reflected signal from the waveguide end and reflectors. We performed the level measurement experiments with non-viscous fluids (diesel, water, and glycerin) at various immersion depths. Also, the waveguide attenuation effects were studied for different waveguide lengths by cutting the long waveguide at every 1 m to understand the attenuation effect while reducing the waveguide’s length from 12.6 m. After that, we calculated the optimal travel distance of L(0,1), T(0,1), and F(1,1) modes with respect to signal strength characteristics while using a long waveguide. This technique can also monitor the fluid’s temperature at multiple locations with respect to the shift in time of flight between each reflector, and end reflected signal.