NON-CONTACT DISCHARGE RADAR RQ-30 / RQ-30A | Water Discharge Sensor



Water Discharge Sensor RQ-30 is a sensor for continuous discharge measurement of rivers, open channels and canals with known cross-section profile. The sensor uses innovative radar technology to measure velocity, water level and discharge. It enables reliable, non-contact measurement without the need for structural work in the water.

The exact and real time knowledge of water discharge is of central importance in the fields of hydrography, water storage management, irrigation and for the early detection of floods. It is essential in hydraulic engineering and water resource management and is the basis for hydrological modelling and simulation. Water Discharge Sensor RQ-30 sensor is a continuous measurement device for the contact-free determination of the water discharge of open rivers and channels.

It combines two sensors in one system. The first determines the water level by measuring the transit time of a radar signal. The second simultaneously measures the flow velocity of the water surface by means of the Doppler frequency shift. These two measurements are internally combined and thus provide the water discharge by using a predefined calibration of the measurement site. Due to the contact-free measurement method Water Discharge Sensor RQ-30 can be installed on extension arms without costly structural measures in the channel or river. This also has the advantage that the sensor is located outside the danger area of flood events and that it requires little maintenance over many years.

Backwater situations caused by inflows, weirs and downstream standing water bodies show no stable relation between water level and discharge. In many situations hysteresis effects with different relations for rising and falling water levels occur. Therefore, the determination of such relations is affected by substantial uncertainty. Only additional information about flow velocity permits the calculation of discharge under these difficult conditions



  • Non-contact, maintenance free measurement system
  • No structural work is necessary in the water
  • No threat to the system through flooding
  • Low power consumption enables operation using solar cells
  • Recognition of flow direction
  • Measuring range 0.08 … 16 m/s (depending on the flow conditions)
  • Recognition of hysteresis-effects
  • Measurement in backwater situations
  • Measures even where weed growth prevails and sensor is not affected by turbidity
  • Measurement in tidal waters
  • Automatic angle measurement
  • Optional (RQ-30a): analogue outputs from 4 to 20 mA

Fields Of Application

The RQ-30 enables discharge measuerment for rivers, streams, open channels and canals for which continuous monitoring is desired. Thanks to the non-contact radar technology the measuring equipment is not susceptible to contamination, debris or driftwood in the water. Furthermore, the non-contact measurement warrants very low maintenance and fail-safe operation especially during high water or flooding.


The sensor can be simply mounted on bridges, on the roofs of closed canals or channel superstructures. The bed of the water should be as stable as possible in order to warrant consistent measurement. A visible swell must be evident on the surface of the water.

Measuring Principle

The non-contact radar technology determines the water surface flow velocity using the Doppler frequency shift method and furthermore the water level is established by a travel time measurement. With known cross section profile the discharge Q of the water can then be calculated on basis of the continuity equation: Q = v· A (h)

Technical Details


  • Dimensions 338 mm x 333 mm x 154 mm
  • Total weight 5.4 kg
  • Protection class IP 67
  • Power supply 6 … 30 V
  • Power consumption at 12V standby approx. 1mA; active operation approx. 140mA
  • Operating temperature -35 … 60°C
  • Miscellaneous over voltage protection, reverse power protection, lightning protection


  • Measurement range 0 … 15 m standard version / 0 … 35 m extended version
  • Resolution 1 mm
  • Radar frequency 26 GHz (K-Band)
  • Radar opening angle 10°


  • Measurement range 0.08 … 16 m/s (depending on flow conditions)
  • Accuracy +/- 0.01 m/s; +/- 1 % FS
  • Resolution 1 mm/s
  • Direction recognition +/-
  • Measurement duration 5 … 240 sec.
  • Measurement interval 8 sec. … 5h
  • Measurement frequency 24 GHz (K-Band)
  • Radar opening angle 12°
  • Distance to water surface 0.50 … 35 m
  • Necessary minimum wave height 3 mm


  • Accuracy +/- 1°
  • Resolution +/- 0.1°


  • Analogue Output (RQ-30a) 4 x output 4 – 20 mA for water level, velocity, discharge and AUX
  • Digital Interface 1 x SDI-12; 1 x RS 485 or Modbus
    • Transfer rate: 1.2 to 115.2 kBd
    • Protocol: various ASCII-protocols
    • Output: water level, velocity and discharge, quality parameters


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