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OTT RLS - Radar Level Sensor

Non-contact water level sensor for long term surface water measurements

The OTT RLS is a non-contact radar level sensor with pulse radar technology. The OTT RLS offers a large measurement range with a small blanking distance and narrow beam width and it easily connects to most dataloggers. The RLS has extremely low power consumption and is ideal for remote or solar powered sites.

  • Surface water
  • Water level / distance to water
  • Non-contact pulse radar
  • Measures water level or depth to water from a bridge, pier or mounting arm
  • 0.4 … 35 m
  • 0.8 … 2 m: ± 10 mm; 2 … 30 m: ± 3 mm; 30 … 35 m: ± 10 mm
  • No
  • SDI-12, RS-485 (using SDI-12), or 4 ...20 mA
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  • No drift over time
  • High Performance–Measurements are unaffected by air temperature, humidity, flood events, floating debris, or contaminated water; reduces the likelihood of missing data and reduces data post processing
  • Low Maintenance–Flat antenna design eliminates nesting areas for insects and periodic maintenance requirement
  • Flexible Integration/Easy Setup–Connects to most data loggers via standard communication interfaces, SDI-12 or 4 ... 20 mA; no need for additional PC software
  • Simple Installation–Light weight compact design facilitates easy mounting on bridges, extension mounting bracket or inside a small protective housing
  • Low Profile Design–Unobtrusive appearance is ideal for urban installation sites or sites prone to vandalism
  • Low Power Consumption–Ideal for remote or solar powered sites; requires only 12 mA when active

For surface water level measurement of:

  • Streams and rivers
  • Tidal zones
  • Reservoirs and lakes

Ideal for monitoring:

  • Surface waters prone to flooding
  • Sediment or debris laden streams and rivers
  • Migrating channels
Leaflet - Radar sensor non-contact water level measurement OTT RLS
Operating instructions Radar Level Sensor OTT RLS (
Operating instructions Radar Level Sensor OTT RLS (
OTT RLS - Declaration concerning to the health of the user
OTT RLS - DIN EN ISO 4373 Declaration of Conformity | Declaration de Conformité | Konformitätserklärung
OTT RLS CSI Specifications
OTT RLS Overview Video
RLS – Firmware - EN
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Water level measurements
Measuring range - distance to water surface 0.4 ... 35 m
Resolution SDI-12 output 0.001 m
Accuracy (SDI-12) 0.4 ... 2.0 m: ±10 mm;
2.0 ... 30 m: ±3 mm;
30 ... 35 m: ±10 mm
Average temperature coefficient (-20 ... +40 °C) 0.01 % full scale/10 K
Accuracy (4 ... 20 mA) ±0.1 % full scale
Average temperature coefficient 10 ppm full scale/°C (at 20 °C)
Measuring time 20 s
Beam angle of antenna (width of beam) 12 º
Electrical data
Power supply 5.4 ... 28 V DC, typ. 12/24 V DC
Power consumption in active mode (at 12 V) <24 mA
Power consumption in rest mode (at 12 V) <0.05 mA
Interfaces 4 ... 20 mA, SDI-12, RS-485 (SDI-12 Protocol)
Housing ASA (UV-stabilized ABS)
Radom (front plate) TFM PTFE
Mounting bracket 1.4301 (V2A)
Lateral axis ±90 º
Longitudinal axis ±15 º
Dimensions and weight
Dimensions L x W x H
Weight (incl. mounting bracket) approx. 2.1 kg
Operating temperature: -40 ... +60 °C
Storage temperature -40 ... +85 °C
Relative humidity 0 ... 100 %
Type of protection
With horizontal mounting IP67 (submersion depth max. 1 m; submersion duration max. 48 h)
EMV limits and radio approvals
EMV for low power radio devices ETSI EN 301 489-3
Low-voltage device safety EN 60950-1
Radio approval for low power radio devices* Short Range Device (SRD)
Europe ETSI EN 300 440
USA FCC 47 CFR Part 15
Canada RSS 210 Issue 7
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How do I communication with my sensor using the RS-485 interface?

Communication on this interface follows the SDI-12 protocol. This follows a specific timing which is defined by the SDI-12 standard. Please find detailed information in the attached/linked document. The sensor wont react to simple ASCII commands send through this interface as they do not conform to the SDI-12 standard.

Regarding PLS Sensor: The RS-485 interface might not be active by default. In this case it needs to be activated using the SDI-12 interface of the sensor. Our HydroService will assist you in this matter (

Regarding CBS Sensor: The active interface of the sensor is determined by dip switches on the device. Please follow the sensor instruction to active the RS-485 interface.

Learn more about the datalogger implementation via RS-485