Feature sponsored by Flow, level & control
bubbles within the wastewater are scanned using an ultrasonic impulse with a defined angle. The resulting echoes are saved as images or echo patterns, and a second scan is conducted a few milliseconds later. The resulting echo patterns are saved, and by correlating/comparing the saved signals, the positions of unambiguously identifiable reflectors can be identified. The reflectors can be identified at varying positions within the images since they have moved with the water. By utilising the beam angle it is possible to compute the particle velocity and hence the wastewater flow velocity from the temporal shift of the reflectors. This technology produces highly accurate readings without the need to perform additional calibration measurements. Designed for operation in channels or pipes, the technology is able to operate effectively in the most demanding, heavily polluted applications. Influencing factors such as flume shape, discharge behaviour and wall roughness are all accommodated within the flow computation. The Nivus cross-correlation technology is able to conduct flow velocity measurements in levels as low as 3 cm, with additional velocity sensors (maximum 9) deployed in larger flows, measuring flow velocity in up to 4 metres of depth. As a consequence of this flexibility, the technology is applicable to a wide variety of flow structures.
The inlet channel at Fowey is 300mm wide so just a single wedge sensor was required, and Nivus provided bespoke bracketry so that it could be deployed quickly under any process conditions.
transmitter, a cross-correlation velocity sensor combined with ultrasonic level measurement. “The popularity of this technology has grown enormously in recent years,” says Rob Rhyder from Nivus. “This is frequently because the flow meter can be quickly and easily retro-fitted to damaged or ageing channels, without having to implement significant capital works.” Explaining the advantages of this solution, Ben
Finney says: “The cross-correlation flow meter was delivered within a month of the order and installation took less than a week. In contrast, work to repair or replace the flume would have taken much longer to organise and implement; it would have cost a great deal more; normal operations of the plant would have been impacted, and there would have been no
Instrumentation Monthly October 2024
guarantee of MCERTS compliance. We were therefore delighted that the Nivus solution was implemented so quickly, and that it passed the MCERTS inspection.”
CROSS-CORRELATION FLOW MEASUREMENT
Nivus has developed a unique ultrasonic cross- correlation method, in which individual velocities are measured continuously at different levels within the flow section. This area velocity flow measurement technique provides a 3-dimensional flow profile that is calculated in real-time to provide reproducible and verifiable flow readings. The flow velocity measurement method is based on the principle of ultrasonic reflection. Reflectors such as particles, minerals or gas
SUMMARY Following the installation of the Nivus NF750 transmitter, the flow measurement facility was tested and passed MCERTS, without any impacts on the plant’s treatment processes. Looking forward, Ben Finney says: “It is likely that we will utilise area velocity flow meters in more applications because they are sufficiently flexible to be able to accommodate a wide variety of hydraulic systems. In addition to the reduced costs and faster installation times, one of the most important advantages is the minimised requirements for process impact.” Emphasising the importance of a partnership approach, Finney adds: “Obviously, we were keen to ensure that the flow installation received MCERTS approval, so it was highly beneficial to accommodate the views of all stakeholders from the beginning, including the MCERTS inspector.” Dave Curtis, South West Water MEICA specialist, says: “More demanding requirements from the regulator combined with challenging process scenarios mean that the need to consider alternative technologies is essential. The Nivus technology has been recognised by South West Water for some time and features on approved equipment lists. The technique offers a valuable tool in our armoury where the application does not suit other closed pipe or noncontact methods.”
NIVUS U.K.
www.nivus.com 79
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