Real-time staggered PRF for in-line industrial fluids characterization

Modern industries need to monitor every step of the production process for a better efficiency and product quality. However, important parameters, like the rheological indexes of the fluids involved in the process, cannot easily be inspected inline, as they are typically analyzed through off-line laboratory tests on specimens. Recently, electronics sensors have been introduced capable to characterize in-line the fluids by acquiring the velocity profile of the fluid flowing in a pipe, and the pressure drop. These sensors are based on Pulsed Wave Doppler (PWD), where ultrasound energy bursts are transmitted at Pulse Repetition Frequency (PRF) rate. The fluid maximum velocity that can be safely investigated in PWD is constrained by the PRF, which is limited by the investigation depth. Unfortunately, in large industrial pipes, the fluid velocity can be easily beyond the Nyquist limit, preventing a correct ultrasound investigation. Staggered PRF is a technique typically used in Doppler radar that, by exploiting PRF sequences at different rate, can recover the right velocity even if beyond the Nyquist limit. In this work, an embedded ultrasound system for in-line rheological investigation is updated by implementing in its Field Programmable Gate Array (FPGA) the staggered PRF technique. Experiments show the system capable of detecting velocity profiles at 25 Hz rate beyond the Nyquist limit.