From 2021, all wastewater treatment plants of a certain size in Saxony-Anhalt are required to provide proof of permanent inflow measurement. However, the Aken Wastewater Association had no measuring system for the main inflow from the north-western part and the secondary inflow from the southern part of its area. With the aim of installing stationary flowmeters at two points in the plant without having to "change the old DN 500 cast iron pipes and the shaft structure", Mr Thomas Heppner, manager and person responsible for the plant, contacted Katronic.

After initial clarification of the technical details, the association received a quote for the KATflow 150 dual-channel flow measurement system. This system for fixed installation with two analogue current outputs (4 ... 20 mA) and two digital relay outputs is particularly suitable as a non-invasive ultrasonic flowmeter for retrofitting existing systems.

After Mr Heppner had received approval for the funding of the project, a trial measurement was first to be carried out at the sewage treatment plant. This will allow a more precise assessment of the subsequent metrological feasibility and the scope of commissioning.

As the conditions for a test measurement on the two DN 500 cast-iron pipes in a shaft structure proved to be inadequate for acoustic sensor coupling due to rust, a number of measures had to be taken in advance to ensure a functional measurement, such as using transducer 'K0' with higher signal strength.

After appropriate preparation of the 'main inlet' measuring point, measured values could be obtained immediately. KATflow 150 flowmeter could then be installed. Initially, no signal could be detected at the second point 'secondary inlet'. Later it turned out that during earthworks near the treatment plant, a DN 200 PE supply pipe was encountered, which seemed to merge into the DN 500 cast iron pipe a few metres further on, where the test measurements had failed. A mobile clamp-on flowmeter was then used to generate a good measurement signal and detect the flow.

At the beginning of their work on site, the commissioned Katronic employees checked new measuring point with the portable clamp-on flowmeter KATflow 200. A measuring signal was present and flow rates could be detected. K1L transducer was then clamped onto the DN 200 pipe and wired to the evaluation unit approximately 35 metres away via an extension cable. The successfully retrofitted KATflow 150 dual-channel flow measurement system is used for simultaneous flow monitoring on two inlet pipes of the sewage treatment plant.

The AZV Aken was able to save a mid-five-figure sum by retrofitting the system, which would have been incurred if a second shaft had been removed and equipped with expensive measuring fittings.