Noninvasive Fluid-Level Sensing in Pipelines Using Ultrasonic Techniques

Accurate fluid-level assessment in sealed pipelines is crucial in wastewater treatment and petrochemical plants, among others. The traditional pulse-echo time-of-flight measurements using ultrasound sensors to measure the fluid level are challenging for low fill levels due to signal contamination with multiple echoes and the resonances in the pipe wall. Though signal-processing strategies such as baseline subtraction and narrowband filtering away from the pipe resonance frequencies improve pulse-echo measurements, low-fill-level detection remains challenging. In this work, we identify these limitations of the pulse-echo technique and propose a resonance-based ultrasonic technique that is accurate and sensitive even at low fill levels. This technique relies on the attenuation of pipe resonances in the presence of fluid, which is validated numerically using time-domain finite-element simulations and experimentally performing resonance measurements on a fluid-filled pipe using an array of transducers. However, the pulse-echo and resonance techniques demand precise calibration with the pipe system before use. To mitigate the need for calibration, we propose a wedge-based phased-array imaging technique based on the total focusing method (TFM) for fluid-level sensing. We discuss the challenges in wedge selection and array positioning and numerically validate the efficiency of TFM to provide better visualization of low fluid levels using a strategy to filter the image artifacts selectively. The presented ultrasonic techniques have significant industrial importance for applications requiring noninvasive fluid-level measurements.