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Discharge Radar Sensor RQ-30d


Discharge measurement for wide rivers with inhomogeneous distribution of flow velocity

With the system of one master-radar sensor and several slave-radar sensors the velocity is measured at several spots throughout the whole water cross-section. Therefore a very high accuracy of the discharge measurement is guaranteed also for very wide water bodies.


Features and advantages

  • Discharge measurement with high accuracy – ideal use for very wide rivers with inhomogeneous velocity distribution
  • One water level measurement and multiple, individual velocity measurements
  • Well proven RQ-radar technique: non-contact measurement, maintenance free system, flood-proof
  • No structural work is necessary in the water
  • Recognition of flow direction and hysteresis effects
  • Measurement in tidal waters
  • Measurement in backwater situations
  • Measures even where weed growth prevails and sensor is not affected by turbidity
  • Measuring range 0.08 ... 16 m/s (depending on the flow conditions)
  • Analogue outputs from 4 to 20 mA (optional)


Fields of application

The main advantage of the RQ-30d is that the discharge can be measured more precisely, especially in rivers and streams where the flow velocity is distributed inhomogeneously over the cross-section. Varying velocities can be observed particularly in very broad streams as well as in situations, where the measuring site is located close to a river bend, an incoming river or watergates. In order to capture the complete flow-profile even more accurately, the RQ-30d system measures multiple individual flow velocities dispersed over the width of the body of water.


Measuring principle

For the RQ-30d (in comparison to the RQ-30) the measuring principle was enhanced: Here the river is split into multiple sections and from each one a partial velocity measurement is taken. One sensor, the master device, additionally measures the water level and distributes this information to all the other devices (= slaves) in the system. Now they are able to calculate the partial dicharge rate per section. Summing up all partial amounts of discharge results in the total discharge at the actual site – continuously, with non-contact to the water and with increased accuracy. The RQ-30d system can be operated with up to seven slave devices at the maximum.


Technical details


  • Dimensions master: 338 mm x 333 mm x 154 mm | slave: 175 mm x 154 mm x 246 mm
  • Total weight master: 5.4 kg | slave: 2.7 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

Waterlevel measurement

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

Velocity measurement

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

Automatic vertical angle compensation

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


  • Interface 1x SDI-12 1 x RS 485 or Modbus
  • Transfer rate 1.2 to 115.2 kBd
  • Protocol diverse ASCII-protocols
  • Output discharge rate, flow velocity, waterlevel, quality parameters

Additional Info

  • Characteristics: stationary measuring system
  • Features: non-contact measurement