Siemens have supplied SWW with a reliable, accurate and most importantly MCERTS approved flow monitoring system for measuring discharge flow from treatment works to meet EA requirements

When South West Water found it necessary to comply with the Environment Agency's strict standards for discharge flow from treatment works, they turned to Siemens Process Instrumentation and Analytics for a flow monitoring system that was reliable, accurate and most importantly MCERTS approved. South West Water in the UK 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 2 million during 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 50 cubic metres a day 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.

South West Water needed a reliable, accurate method to measure and document flows at its various sites to meet these regulatory reporting requirements.

For this reason, a flow monitoring plan was implemented, covering 226 sites.

The programme was implemented in five phases by installation contractor May Gurney.

The company selected the Siemens HydroRanger 200 ultrasonic instruments because of their accuracy, reputation for 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, the 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 the first flow instruments 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 Modbus protocol built-in to the HydroRanger may also be used to communicate instantaneous values of flow.

'The implementation used both open channel and closed conduit flow measurement techniques,' said Dave Curtis, Systems Engineer (SCADA Engineering Systems) with South West Water, '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.

We are very impressed with the performance of the instrumentation and the support from the Siemens team.

The flow monitoring plan made South West Water fully compliant with the Environment Agency 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.

Siemens instrumentation equipment provided significant benefit to the project,' says Gary Jones, Project Manager with May Gurney.