Flow Measurement & Control

Water meter does not require straight inlet and outlet runs

May 2015 Flow Measurement & Control

According to Krohne, two important limitations must be taken into account when using electromagnetic flowmeters (EMF) in water networks. On the one hand, the flow rates in the networks are sometimes extremely low. This often occurs at night but it can also happen when a pipeline is oversized as a consequence of planning. Due to the low flow velocity, low flow rates are not easy for electromagnetic flowmeters to measure.

On the other hand, electromagnetic flowmeters generally require sufficiently long, straight inlet and outlet runs to achieve the measuring accuracy specified by the manufacturer. Abnormal flow profiles, such as those that occur following pipe bends or slide valves, affect the measuring result and must be homogenised by providing long inlet and outlet runs. Since these conditions are not always met in practice, the goal when designing the Waterflux electromagnetic water meter was to have a device that could accurately measure both large and small flows without requiring a specific shape or length of inlet and outlet run.

Independent testing has now confirmed that this goal has been achieved: The Physikalisch-Technische Bundesanstalt (PTB; National Metrology Institute) in Berlin studied the behaviour of different measuring tube cross sections during changing flow profiles.

The performance of a conventional EMF with a round cross section was compared to that of the Waterflux electromagnetic water meter. Both devices were installed and tested with inlet and outlet runs of varying lengths and downstream from a bend in the pipe. Results showed that the Waterflux was considerably less sensitive to the installation position. Its measuring tube is constricted on the inside, changing the profile to a rectangular one and thus increasing the flow velocity, creating a uniform flow profile and reducing or completely eliminating turbulent fluctuations in the flow profile. This allows the device to measure even extremely low flow velocities with superior accuracy.

Waterflux is an electromagnetic flowmeter for applications in the field of water and wastewater and designed for custody transfer according to European Directive MI-001. The measuring accuracy reflects the most recent specifications of the ISO/EN, MI-001 and OIML standards. It lies within legal requirements with a ratio of 400 between Q1 and Q3. The high operating frequency of 1 Hz to 1/20 Hz guarantees reliable measurement results with rapid inflow and outflow rates.

For more information contact John Alexander, Krohne SA, +27 (0)11 314 1391, j.alexander@krohne.com, www.krohne.com


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