Ultrasonic non-invasive flow measurement is eliminating pipe damage concerns and conserving precious water
To properly manage leakage or unaccounted losses, accurate measurement is crucial.
Clamp-on ultrasonic flowmeters are proving to be an essential water management tool in the targeted water loss initiatives of water and wastewater service providers around the globe. Because measurement is carried out safely from the outside of the pipe, there is no risk of costly and disruptive pipe damage due to the invasive techniques involved in the installation of conventional wetted flowmeters.
With two measuring channels, which in reflect mode provide four paths through the flow profile, or even four measuring channels, producing eight paths through the fluid in reflect mode, the flowmeter is able to reliably average the result of two or four planes.
Performing under even the most challenging conditions and finely tuned to low flow velocities, ultrasonic flowmeters are simply attached to the outside of the pipe wall, offering a highly versatile and accurate measurement solution for the water and wastewater industries.
What are the accuracies of ultrasonic, clamp-on measurement?
While doppler measurement is frequently recommended for wastewater flow measurement, as performance is stated as having an accuracy of ±2% of readings on liquids with entrained particles, or gases of 100 microns or larger and minimum concentrations of 75 ppm, this is rarely the case in practise. Despite specification claims, with constantly varying percentages of entrained air or suspended solids, doppler installed accuracy seldom exceeds 10%.
Ultrasonic transit time measurement on the other hand, uses transducers that typically operate in the 0.2-2 MHz frequencies, and works by sending two ultrasonic pulses through the medium – one in the direction of flow, and a second one against it. The transducers are alternately working as a transmitter and a receiver; ultrasound sent with the flow direction speeds up, whilst against the flow slows down, and the time difference, Dt, is directly proportionate to the flow rate.
Curbing the flow of non-revenue water.
A major headache for many water utilities, non-revenue water is water that has been treated, but lost before it reaches the consumer, through issues such as leaks or even theft from illegal connections in the distribution lines.
A chief water concessionaire in the Philippines had tasked FLEXIM with flow measurement on a 3.2m concrete pipe at the inflow to a reservoir, as they were keen to greatly reduce non-revenue water. They had already had some success by employing state of the art leak detection equipment, but were very much focused on achieving a further reduction.
The 3.2m transport pipe was interconnected with a similar transport pipe in a second plant, so to carry out accurate measurement, conduct water balance and identify any losses within that particular segment, water engineers were looking for a way to retrofit a flowmeter that wouldn’t involve having to make modifications to the pipe. Any alterations could potentially weaken or damage the pipe, so non-invasive technology such as clamp-on ultrasonic measurement was the obvious solution. Precise installation of four pairs of transducers would also need to be carried out, which on a 3.2m pipe is not always an easy feat.
Reliable and precise recording of water flow to the reservoir.
Following a series of on-site trials and testing to check functionality and appropriate design of the transducers to be used, ultrasonic clamp-on technology was proven to be up to the challenge of delivering reliable and accurate flow measurement on a permanent basis. Precisely recording the water flow to the reservoir, measuring data is relayed to the plant’s process control system via HART protocol.
For more information, contact Andy Hammond – www.flexim.co.uk | sales@flexim.co.uk | +44 (0)1606 781 420
