The Fernwasser Elbaue-Ostharz (FEO) is a long-distance water network of 800 kilometres in length covering several different regions of Germany. The network is comprised of large pipelines up to DN 1200 which transport around 220 million litres of drinking water to the central German region every day. One of the three waterworks in the network, the Wienrode, is connected to the Rappbode dam of the Talsperrenbetrieb Sachsen-Anhalt AöR. Once the transported raw water has been treated it provides about 40% of the drinking water requirement of the Saxony-Anhalt region.

Part of the infrastructure of the Wienrode waterworks, operated by FEO, is a bypass system connecting two individual 800mm supply pipes to the waterworks. Two Katronic KATflow 150 clamp-on ultrasonic flowmeters are installed on these bypass pipes and are used to control the flow at these critical points.

When using ultrasonic measurement technology, it is essential to ensure that there are sufficient inlet and outlet distances to ensure an axially symmetrical flow profile. Before deciding on a stationary unit from Katronic, FEO carried out three tests with minimum and maximum process peaks at different points to find the optimum position for the measurement. The decisive factor in the purchase of the two dual-channel flowmeters was the success of the previous tests and the associated prospect of being able to reliably measure large volumes of water in a turbulent environment with the KATflow 150.

The driving factor of the measurement comes from the requirement of the dam's waterworks to supply the region's drinking water. This pipeline operates around the clock with a typical capacity of approximately 6000 m³/h. In the bypass system the water is usually divided equally between the two pipes and is used whenever the turbine fails or cannot guarantee the inflow required by the waterworks.

Both KATflow 150 are dual-channel measuring instruments with an analogue 4 ... 20 mA process output and a Profibus PA interface. The client’s control system receives four measured values simultaneously and are used for quality control. A critical factor in the installation is to achieve redundancy of the flow measurement channels. If one sensor or signal input fails, the flowmeter detects this and switches to the signal that is still available. If the current output signal drops to 0 mA, the programmable logic controller (PLC) switches to a substitute value and deactivates the control.

Although the location where the KATflow meters are installed is not ideal owing to the presence and influence of two annular piston valves, both devices have proven themselves capable of meeting the challenge of this application. The flows are turbulent and axisymmetric at both measurement points and the measurement is not helped by the proximity of the control valves. The PLC is used to limit the flow through the works by varying the degree of opening of the valves with the flowmeters providing the data needed to allow this remote control function. The data collected at the plant shows that the Katronic flowmeters' measurements are 98% usable, despite the extremely difficult measuring conditions.