Design of Miniature Clamp-On Ultrasonic Flow Measurement Transducers

Abstract

Clamp-on ultrasonic transit-time difference measurements of liquid flowrate are widely used in industry for both flow metering and heat metering applications. However, the sensors used tend to be relatively large, hindering their use on small diameter pipes, and using more material in the transducer wedge than is strictly necessary. The accuracy of the technique depends on a number of factors, and particularly on the accuracy of the compression wave speed in the liquid that is used in the calculations to obtain flowrate or heat transfer rate from the liquid in the pipe. Many flow meters either assume a value for the wave speed or obtain it using thermocouple measurements of the pipe exterior with a look-up table or simple equation. An error in the liquid ultrasonic velocity relates directly to errors in the calculated flowrate. It is highly beneficial if the ultrasonic wave speed in the liquid can be accurately measured in real time for flowrate calculations, especially for temperature and pressure varying conditions. A new type of small clamp-on ultrasonic transducer is reported, using a 6mm wide PEEK wedge that contains two piezoelectric elements, one of which generates sound normal to the flow direction, yielding the measurement of ultrasonic wave speed in the liquid. The new transducers were tested on a small rig with a 15mm diameter copper pipe and a 70mm diameter stainless steel pipe, yielding accurate measurements of liquid ultrasonic velocity and flowrates.

clamp-on AND transit time difference AND smart meter

“…However, on analysing the second pulse in the blue waveform of figure 4 (2 V* at ~70 μs), we find that the results indicate that only one correction factor is required across the entire range of flow. Figure 4 below shows the measured transit time difference with flow rate from the 2V* mode shown in figure 4 [9]; it is linear across the entire flow range, where for this copper pipe with an inner diameter of 13.6 mm and an outer diameter of 15 mm, the laminar to turbulent flow transition should occur at around a flow rate of 20 ml/s. 7mm wall thickness copper pipe if the wave propagated as a simple multiple number of V-paths, as would be the case for a larger diameter pipe.…”

“…The ultrasonic transducers reported here are constructed using 30mm long, 6mm wide PEEK (polyether ether ketone) wedges, that can be injection moulded. The size of the 0.5 mm thick, 4 MHz PZT piezoelectric element used in these transducers is 5mm x 10mm, with a PEEK wedge angle of 38° [7,9]. The transducers are driven by a 4 cycle, 10 Vpk-pk sinusoidal wave pulse.…”

Transducer Design for Clamp-on Guided Wave Flow Measurement in Thin-Walled Pipes

“…The design shown in Fig. 5(a) is the original design that was reported in reference [14], but without the scattering surface. Design (a) represents the simplest solution for comparison with the other designs.…”

“…Designs (d) and (e) are smaller than the other designs, so they require ∼45% the amount of PEEK material. They are also simpler to machine as they have no enclosed holes, although in mass production all of the designs are small enough to be injection moulded [14]. Both (d) and (e) have the scattering face to reduce internal reflections; the contact face of (d) is flat, whilst that of (e) also features the curved contact face.…”

Low‐Cost Photoelectric Flow Rate Sensors Based on a Flexible Planar Curved Beam Structure for Clinical Treatments

“…However, conventional ultrasonic sensors are incapable of accurately measuring pipelines with small diameters (<8 mm) due to low measurement accuracy, instability, and small transit time difference. [21][22][23][24][25][26] Due to the progress in microelectromechanical system (MEMS) technology, various research studies have proposed flow rate sensors that rely on piezoelectric micromachined ultrasonic transducers (PMUTs). These sensors can measure flow in pipelines with a diameter of 4 mm.…”