Continuous differential level monitoring for automated rake control

Automated and reliable rake control is achieved through continuous differential level monitoring before and after the rake. Using two Micropilot FMR20B radar sensors combined with FlexView FMA90, the solution ensures early clogging detection, stable screening operation and reduced manual intervention, even in the presence of foam, suspended solids, debris and fluctuating solids loads.

Reliable differential level monitoring enables early clogging detection and automated rake cleaning before overflow occurs. Manual intervention is significantly reduced, leading to higher screening availability and improved operational stability. Clear visualization, logged trends and digital communication provide full process transparency and support proactive maintenance strategies. The result is an efficient, robust and scalable solution for rake control that keeps wastewater screening systems operating reliably under challenging conditions.

In wastewater screening zones with measuring ranges below 5 m, foam formation, turbulence and fluctuating flow conditions often affect the performance of conventional level measurement technologies. At the same time, suspended solids, sediments and accumulated screenings increase the risk of clogging and overflow, particularly in coarse and fine screening applications.

To ensure stable screening operation, early detection of contamination buildup is essential. This requires reliable differential level measurement before and after the rake. Manual inspection and cleaning are time‑consuming, increase downtime and pose safety risks, while environmental influences such as debris and changing contamination levels further complicate consistent monitoring.

A simple start to smarter control is achieved by combining non‑contact radar level measurement with automated differential level evaluation and control. Micropilot FMR20B continuously measures the water level before and after the rake using its focused 80 GHz radar beam, ensuring stable, non‑contact measurement even in the presence of foam, turbulence or suspended solids.

Both level signals are transmitted to FlexView FMA90, which calculates the differential level, the key indicator for early clogging detection. FlexView FMA90 enhances the sensors and brings every insight into clear view by continuously processing the incoming level values, calculating the differential level and comparing the results with configurable limit values. FlexView FMA90 can evaluate either the differential level or the ratio between upstream and downstream levels for reliable rake control.

When the differential level exceeds the configured limit, FlexView FMA90 can automatically initiate the rake cleaning cycle. This prevents overflow, stabilizes the screening process and significantly reduces the need for manual intervention. Level values, differential level and system status are visualized in real time, providing operators with full visibility over screening performance.

Trend logging and event tracking support proactive maintenance and long‑term operational stability. Process values such as individual levels, differential level and system status can be transmitted to the control system via Modbus TCP or HART communication. Guided setup sequences and automatic sensor detection via HART ensure fast commissioning and reliable operation. The integrated web server additionally enables convenient access to measurement values. For secure integration into modern infrastructures, FlexView FMA90 was developed according to IEC 62443‑4‑1 secure product development requirements.