The Endress+Hauser FDU91 is an ultrasonic level sensor from the Prosonic S family, designed for continuous, non-contact, and maintenance-free level measurement of fluids, pastes, sludges, and powdery to coarse bulk materials . It is also suitable for flow measurement in open channels and measuring weirs . The measurement is unaffected by dielectric constant, density, or humidity, and the self-cleaning effect of the sensor reduces build-up formation .

The sensor features a hermetically welded PVDF construction, making it weather-resistant, flood-proof (IP68), and suited for rough ambient conditions . It offers a maximum measuring range of 10 m (33 ft) for liquids and 5 m (16 ft) for solids. The FDU91 can operate in process temperatures from -40 to 80°C (-40 to 176°F) and pressures from 0.7 to 4 bar (10 to 58 psi) . It is designed with time-of-flight correction for high accuracy and features threaded process connections for easy installation. The sensor is also suited for use in explosion hazardous areas .