Photo: Schematic illustration of multiple measurement paths Photos: Transmitter and various sensor types
Thanks to novel CFD models (Computational Fluid Dynamics) and comprehensive testing at renowned institutes, influence and behaviour of flow profiles downstream of standard disturbances could be examined. Based on the results it is now possible to integrate flow profiles downstream of elbows and other disturbances into calculation models directly in the transmitter of the measurement system. Only the type of disturbance and the distance to the measurement spot need to be specified. From these specifications the measurement automatically determines the correction factors to use. The result of the flow measurement is therefore highly accurate and can be even used together with shorter calming and intake sections.
Photo: CFD-model of a disturbance (elbow)
The new NIVUS GmbH device types allow using the transit time method both as invasive measurement and clamp- on system. Here the type of sensor used must be selected depending on the situation on the measurement place.
Highest measurement accuracy can be achieved by using a multi- path system with wetted sensors in a defined arrangement. If it is not possible to insert the sensor into the process (abrasive, corrosive or other problematic media), the sensors can be installed on the pipeline from the outside without process interruption (clamp-on measurement system).
Implementing a Measurement
Tasks of the example depicted: long-term recording of flow rate and flow velocity for archiving in a distribution system operator’s drinking water supply pipeline.
Accuracy requirements in this case are very high since the measurement place is to be used for billing purposes. A NivuFlow 600 system with invasive sensors by NIVUS GmbH was used. The sensors were inserted into the pipe by using tapping nozzles. This is how the readings could be provided to the following SCADA system with the required level of accuracy via data connection. The variety of sensors and installation material allows picking up readings at various measurement spots.
A very minimalistic approach can be followed in terms of spare parts stock: no need to stock diameter-specific parts, one measurement system for almost all pipe diameters and measurement places.
Summary
Flow measurements based on the ultrasonic transit time difference principle have not only undergone many years of extensive testing. They have also proven successful in practical use and stand out for a high level of accuracy and flexibility in terms of applicability in various measurement places. Thanks to robustness and ease of maintenance the ultrasonic transit time principle is perfectly suitable for both measuring in pipes with smaller diameters (such as process water or cooling water) as well as for permanent measurements on demanding measurement sites (such as large pipe diameters, hydro-electric plants, high process water volumes and varying media). With new-generation devices, however, the benefits of the method have been significantly extended. Among other things, measurement ranges and accuracies of flow measurements have been increased considerably.
Literature
EN ISO 6416 (2005), Messung des Abflusses mit dem Ultraschallverfahren (akustisches Verfahren)
EN ISO 748:2000 (2000), Durchflussmessung in offenen Gerinnen
Dr. Solliec, Laurent. (2013). Real time flow rate modelling in disturbed conditions from velocity profilers. Strasbourg. Technische Unterlagen der Fa. NIVUS GmbH, Eppingen (2016)
Author Contact Details Ralf Brüning Dipl.-Ing. (FH). Product Manager, Nivus GmbH • Im Täle 2, 75031 Eppingen, Germany • Tel +49 7262 91910 • Email:
ralf.bruening@
nivus.com • Web:
www.nivus.com
www.envirotech-online.com IET Annual Buyers’ Guide 2016/17
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