SWW uses Siemens ultrasonics

South West Water (SWW) provides water and sewerage services to customers in Devon, Cornwall and parts of Dorset and Somerset - a large region with a population of 1.5 million residents. This figure increases to more than two million during the summer tourist season, and as a result there is a wide variation in water system demand and flows.

In recent years, the company has upgraded treatment works, pumping stations, and sewers to meet tighter standards set by the Environment Agency (EA). The EA has developed a monitoring and certification standard for inspection and production of quality monitoring data and operator self-monitoring known as MCerts.

Regulations strictly limit discharge flows from treatment works, and require water companies to measure and record the volume of effluent flow from works that have consent to treat in excess of 50m3 daily with an uncertainty of no more than +/-8%.

Where the storm overflow setting can be adjusted, the flow to treatment must be measured and recorded during periods when excess flow is diverted to storm capacity holding tanks.

SWW needed a reliable, accurate method to measure and document flows at its

various sites to meet these regulatory reporting requirements. As a result, a flow monitoring plan was implemented covering 226 sites. The program was implemented in five phases by installation contractor May Gurney.

The company selected Siemens’ HydroRanger 200 ultrasonic instruments because of their accuracy, reliability, and because they are MCerts, Class 1 approved. This certification assures users that the instruments have passed a rigorous set of lab and field tests conducted over three months by Sira, an independent product certification body appointed by the EA.

MCerts certification means a product meets EA, national and international performance standards. In fact, the Siemens HydroRanger 200 controller and Siemens OCM III open channel meter are one of the first flow instruments to be certified by the EA. Echomax transducers (sensors) are located on flumes, weirs and channels to continuously monitor water level. They provide data to the HydroRanger 200 controllers, which calculate flow and feed the information into a Programmable Logic Controller (PLC). The PLC formats the required data, which is relayed to the Central Data Archive in Exeter via telemetry. The HydroRanger’s built-in Modbus protocol may also be used to communicate instantaneous values of flow.

Dave Curtis, systems engineer (SCADA Engineering Systems) at SWW, says: “The implementation used both open channel and closed conduit flow measurement techniques. Once several sites had been commissioned, it was possible to create and refine a generic template and then only site-specific parameters needed to be modified.”

He adds: “The flow monitoring plan made South West Water fully compliant with

the Environment Agency’s requirements for self-monitoring of effluent flow. The Siemens instruments are Mcerts-certified so their readings are readily accepted by the EA. The flow data is also useful for on-going asset management, demand analysis and future planning.”

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