Endress+Hauser Prosonic FDU91 – Reliable Ultrasonic Sensor for Level and Flow Measurement

The Prosonic FDU91 is a non-contact ultrasonic sensor designed for continuous measurement of liquids, pastes, sludges and bulk solids. Combined with Endress+Hauser FMU90/FMU95 ultrasonic transmitters, it provides a reliable solution for level measurement and open channel flow applications.

Using the proven time-of-flight ultrasonic measuring principle, the FDU91 delivers stable measurement performance without contact with the process medium, reducing maintenance requirements and avoiding mechanical wear.

Accurate Measurement Without Contact

The FDU91 calculates level based on the travel time of ultrasonic signals reflected from the medium surface. Since the sensor does not touch the measured material, it is suitable for applications where contamination, corrosion or changing media properties may affect traditional contact measurement technologies.

Key performance:

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  Measuring principle: Ultrasonic time-of-flight
  
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  Accuracy: ±2 mm + 0.17% of measured distance
  
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  Maximum measuring range:
  
  
  Liquids: up to 10 m
  
  
  Solids: up to 5 m
  
  
  
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  Blocking distance: 0.3 m
  
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  Process temperature: –40 to +80 °C
  
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  Process pressure: 0.7 to 4 bar abs
  
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  Sensor material: PVDF
  
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  Protection rating: IP68 / NEMA 6P
  
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  Communication (via transmitter): HART, PROFIBUS DP
  

Suitable for Liquids, Sludges and Bulk Materials

The Prosonic FDU91 is designed for versatile industrial measurement tasks and can handle different types of media without being influenced by:

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  Dielectric constant changes
  
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  Density variations
  
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  Humidity changes
  
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  Medium buildup on the sensor surface
  

Typical applications include:

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  Water and wastewater tanks
  
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  Chemical storage vessels
  
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  Sludge measurement
  
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  Bulk material silos
  
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  Stockpiles and crushers
  
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  Open channel flow measurement
  
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  Measuring weirs and channels
  

Self-Cleaning Effect for Reduced Maintenance

The sensor design provides a self-cleaning effect that helps reduce material buildup on the ultrasonic surface.

This makes the FDU91 particularly suitable for applications involving:

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  Dusty environments
  
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  Sludge and wastewater
  
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  Sticky materials
  
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  Outdoor installations
  

The fully welded PVDF construction also provides strong chemical resistance and long-term durability.

Flexible Installation with Separate Transmitter

The FDU91 uses a separated sensor and transmitter design, allowing installation flexibility in demanding environments.

The sensor can be installed up to 300 m away from the transmitter, making it suitable for large tanks, outdoor measurement points and applications where electronics need to be installed in a protected location.

Compatible transmitters include:

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  Liquiphant FMU90
  
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  Liquiphant FMU95
  

The separated architecture helps simplify maintenance and improves installation adaptability.

Integrated Temperature Compensation for Stable Accuracy

Temperature changes can influence ultrasonic signal propagation. The FDU91 includes an integrated temperature sensor that compensates for temperature effects, helping maintain accurate measurement performance under changing environmental conditions.

Reliable Solution for Water, Wastewater and Industrial Applications

The Prosonic FDU91 is widely used where reliable, economical and maintenance-free level measurement is required.

Typical industries include:

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  Water & wastewater treatment
  
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  Chemical processing
  
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  Mining and minerals
  
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  Power generation
  
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  Bulk material handling
  
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  Environmental engineering
  

With its non-contact design, robust construction and flexible installation options, the FDU91 provides a dependable ultrasonic measurement solution for challenging industrial environments.

Frequently Asked Questions

What is the Endress+Hauser Prosonic FDU91 used for?

The FDU91 is used for continuous non-contact level measurement of liquids, sludges, pastes and bulk solids, as well as open channel flow measurement.

What is the maximum measuring range of the FDU91?

The maximum measuring range is 10 m for liquids and 5 m for solids.

Does the FDU91 contact the measured medium?

No. The FDU91 uses a non-contact ultrasonic measuring principle, which reduces wear and maintenance requirements.

Which transmitter is required for the FDU91?

The FDU91 is designed to work with Endress+Hauser FMU90/FMU95 ultrasonic transmitters.

Can the FDU91 be used outdoors?

Yes. The IP68 / NEMA 6P protection rating and robust PVDF housing allow use in demanding outdoor environments.

What communication protocols are available?

Communication is provided through the connected transmitter, supporting options such as 4–20 mA HART and PROFIBUS DP.