High accuracy, low cost ultrasonic clamp-on flow metering of small diameter, thin walled pipe

A new, miniature design of a clamp-on ultrasonic transit-time difference flow meter for use in liquids is presented, with particular application to small diameter, thin walled metal pipes, opening up new areas of application, including smart water metering. The particular embodiment of the hardware is low cost and can be installed by unskilled users, and uses a type of guided wave mode that is significantly different to previous examples of clamp-on flowmeters that have used a leaky guided wave in the pipe to generate compression waves in the liquid. In the example presented in this paper, the entire liquid-pipe system acts as a wave guide, providing large amplitude ultrasonic signals with outstanding signal to noise, even from a drive voltage of just a few volts. The flowmeter is capable of measuring flow rates down to a few millilitres per second, with an accuracy better than 0.5 millilitres per second. The results presented mainly focus on 15 mm diameter copper pipes of wall thickness 0.7 mm, but the same approach works well on pipes with larger diameters and slightly thicker walls, up to around 30mm diameter in the current embodiment, In many instances, in previous work, the presence of the guided wave modes has prevented clear interpretation of the ultrasonic signals that are detected