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SLD – Side Looking Doppler Sensor



SLD – Side Looking Doppler Sensor


Water flow meter for longterm data collection of velocity and discharge measurements

The OTT SLD is a measurement system for continuous measurement of water velocity and level in streams, rivers, and canals. The sensor employs the acoustic Doppler principle to reliably measure flow velocity in a variety of naturally occurring conditions, including during most flood events.

  • Fixed installation
  • Acoustic
  • Flow velocity
  • Side-Looking-Doppler for continuous discharge measurement in rivers and open channels. Discharge calculation based on velocity – index – method. Integrated vessel filter algorithm, Modbus interface and output of total volume of flow (max. interval 1 day).
  • ± 10 m/s
  • ± 1 % of measured value ± 0.5 cm/s


  • Equipped with two horizontal ultrasonic transducers “looking sideways” into the flow (Side Looking Doppler) to measure water velocity.
  • An optional vertical transducer and integrated pressure cell measures the water level.
  • All measurement values are analyzed, verified and processed by an integrated signal processor, before being used in the calculation of discharge.
  • Velocity measurements from up to nine cells are used, along with measured water level, to calculate discharge either internally in the OTT SLD or externally in a data logger.
  • All measurements can be retrieved using SDI-12, RS485 , RS232 or Modbus RTU protocols and are available for storing in a data collection platform, such as the OTT netDL station manager.


Flow velocity measurement  
Measuring range ±10 m/s
Accuracy 1% of measured value ± 5 mm/s
Number of measuring cells 9
Cell size / Blanking  
600 kHz 2 … 10 m / 0.5 … 30 m
1.0 MHz 1 … 4 m / 0.3 … 15 m
2.0 MHz 0.2 … 2 m / 0.1 … 8 m
Beam angle / Max. profiling range*  
600 kHz 2.4° / 80 m
1.0 MHz 2.4° / 25 m
2.0 MHz 2.1° / 10 m
Minimum coverage 0.15 m (water level option)
Electrical data  
Supply voltage 12 … 16 V DC, typ. 12 V
Power consumption 50 … 500 mW, depending on measurement cycle
Water level measurement  
Measuring range 0.15 … 10 m
Accuracy ±3 mm, depending on stratification
Pressure cell (optional)  
Measuring principle Piezo-resistive
Measuring range 0 … 10 m
Accuracy ±0.25 % FS
Interfaces RS-232, SDI-12 or SDI-12 via RS-485, Modbus (optional)
Environmental conditions  
Operating temperature -5 … + 35 °C
Storage temperature -20 … +70 °C
Length x Ø 45 … 52.2 cm x 7.5 cm
Housing material POM
Wall bracket (accessory)  
Components Bracket, protective cover, and C rail mount
Material Stainless steel
Details On request
Discharge calculation Within the unit or externally on a data­logger, e.g. OTT netDL
OTT SLD EasyUse Installation and service software System setup, commissioning, reviewing and optimizing
OTT Prodis 2 (accessory) Calibration software Determining correction factors, (velocity-index method and others), optimizing discharge calculation, managing stations
*The beam angle is understood to be the measured angle with regard to the main axis. The maximum profiling range depends on the water profile, salinity, suspended matter content etc.