Starflow QSD

Model 6527B and 6537A Starflow QSD

  • Overview

    The Unidata 6527 Starflow QSD SDI-12 and Modbus Instrument is used to measure water velocity, depth and temperature of water flowing in rivers, streams, open channels and large pipes. When used with a companion Unidata IP data logger, flow rate and total flow can also be calculated.

    The 6527 Instrument is robust, reliable and easy to use. It is completely sealed against water ingress, low maintenance, low power, no calibration and no fussy power arrangements required.

    Ultrasonic Doppler Principle in Quadrature Sampling Mode is utilised to measure water velocity. The 6527 Instrument transmits ultrasonic energy through its epoxy casing into the water. Suspended sediment particles or small gas bubbles in the water reflect some of the transmitted ultrasonic energy back to the 6527 Instrument’s ultrasonic receiver instrument that processes this received signal and calculates the water velocity.

    The 6527 Starflow QSD incorporates ultrasonic depth sensor and an absolute pressure depth sensor. An ultrasonic depth sensor measures the water depth using the ultrasonic principle and has a range of up to 5m. An absolute pressure sensor measures pressure forces applied to the strain gauge. The absolute, non-vented, sensor reports a value equal to the sum of the water pressure and the atmospheric pressure above the water. In order to compensate for the atmospheric (barometric) pressure fluctuation, the 6527 Starflow QSD should be connected to the 6515 Starflow QSD barometric reference. The absolute pressure sensor has a range of up to 10m. Having sensors using different depth measurement methods provides flexibility in-depth measurement.

    The 6527 instrument’s low profile form factor minimises disturbance to the flow it’s measuring. Furthermore, 6527 instrument measures velocity in both directions and is suitable for use in a wide range of water qualities, from sewage to potable water, seawater too.

    With a companion Unidata data logger or a telemetered Neon Remote Logger, the instrument can be programmed to compute flow rate and total flow in pipes and open channels of known dimensions.

    The Unidata 6537 Starflow QSD SDI-12 and Modbus Instrument has a 4 electrode electro conductivity instrument (EC) included for measuring the quality of the water. Water quality is measured on an ongoing basis and this parameter can be recorded along with velocity and depth to better analyse the nature of the water in open channels and pipes. Conductivity is a very important water quality measure and any spike on the conductivity is a strong indicator of a pollution event.

    The Unidata 6515 Barometric Reference is a barometric reference module which is used with the Starflow QSD instruments to correct the pressure sensor depth sensor readings for atmospheric pressure variations.

    The 6515 barometric reference is a module which is installed in line with a Starflow QSD Instrument to monitor the barometric pressure in the geographical location of the instrument. With this module barometric compensation can be achieved for the depth sensor within the Starflow QSD Instrument, so the depth sensor provides pressure and derived depth readings which are corrected for differences in atmospheric pressure.
    6515 barometric reference inbuilt electronic components communicate with the Starflow QSD instrument via a dedicated protocol providing regular atmospheric pressure readings. These values are then applied to the pressure sensor, allowing the Starflow QSD Instrument to report true atmospheric pressure compensated depth readings.

    An alternative to using 6515 barometric reference can be any other electronic barometer, which is read and then the depth readings are corrected for atmospheric pressure in another system, such as another data logger or an RTU connected to the SCADA system.

    Another alternative to this barometric reference could also be to consult the local weather service and obtain the current barometric pressure for the geographical location that the Starflow QSD Instrument is deployed and use those readings as a depth compensation factor in an end system where the velocity and depth data is being stored.

    Starflow QSD Ultrasonic Doppler velocity and depth instrument
    Starflow QSD Ultrasonic Doppler Velocity, Depth and Conductivity Instrument
    6515 Barometric Reference

  • Specifications 6527B and 6537A

    Physical specifications

    Material: Epoxy-sealed body, Marine Grade 316 Stainless Steel Mounting Bracket
    Size: 135mm x 55mm x 22mm (LxWxH)
    Weight: 1kg with 15m of Cable
    Operating temperature: 0°C to 60°C water temperature

    Velocity and Depth specifications

    Velocity Range:
    – 20mm/s to 0.8m/s
    – 20mm/s to 1.6m/s in one direction (default)
    – 20mm/s to 3.2m/s
    – 20mm/s to 13.2m/s
    – Bidirectional velocity capability, set using configuration tools
    Velocity Accuracy: ±1% typical

    Depth Range Ultrasonic Sensor:
    20mm up to 5m above top surface of the instrument
    40mm up to 5m from the base of the instrument
    Depth Accuracy Ultrasonic Sensor :Typical ± 1%

    Depth Range Absolute Pressure Sensor: 0 to 10m
    Depth Accuracy Absolute Pressure Sensor:
    Typical ± 0.19% for 0m to 5m range
    Typical ± 0.38% for 0m to 10m range

    Temperature: 0°C to 60°C
    Temperature Resolution: 0.1°C

    Flow Computation: Flow rate, totalised flow with companion NRT/NRL
    Channel type: Pipe, open channel, natural stream

    Conductivity (6537 Only): 0-200,000uS/cm Typically ±1% of measurement, returned either as
    16-bit value (0 65535uS/cm) or 32-bit value (0-262,143uS/cm)
    Compensation Conductivity (6537 Only): 25°C default / set using configuration tools

    Cable: 15 metre, 6 way
    Cable Options: User specified up to 50 metres

    Electrical specifications

    Power Source Typical: External Battery 12V – 24V DC
    Power Usage: 10V to 24V DC, 50µA standby, 100mA active for 1 sec
    SDI-12: SDI-12V 1.3 recorder (1200 baud smart instrument channel)
    RS 485: Modbus RTU

    Specifications 6515

    Size: 75mm x 45mm x 20mm (LxWxH)
    Pressure Range: 0 to 100kPa
    Accuracy: 0.25% FS

  • Ordering Information

    Full product consists includes mounting bracket

    Model Description
    6527A Starflow QSD SDI-12 Instrument
    6527A-S Special cable length (up to 50m) Starflow QSD SDI-12 Instrument

    Sales Enquiry Form

    Please use the form below for an enquiry to our sales team.







  • Documents

  • Q: Does the velocity measurement has a ‘dead band’ close to the ultrasonic eyes and if so, what is the dead band distance?

    A: The QSD has a half-power beamwidth of 2.8 deg which means the transmitter & receiver beams begin to intersect about 100mm from the face of the instrument. However, this is the half-power width; lower power intersection occurs closer than 100mm and given the receiver sensitivity will contribute to the velocity detection. Suspended particles reflect the signal at many angles, so even before the beams intersect there will be high angle Doppler reflections that are received.
    Also, the beams will be internally reflected off a shallow water surface and mix further “upstream” so it is difficult to determine where the maximum signal is coming from and even more difficult to say if there is a dead band and how large it is.
    Hence, the zone of maximum sensitivity lies from 100mm to 300mm from the instrument but it depends on water level (reflection) and quality (number of reflectors). The instrument will detect velocities from 25mm onwards.

    Q: Can the Starflow QSD be used in small pipes

    A: We have been testing the operation of QSD’s in a 150mm pipe for some months now.
    The performance of QSD’s in this arrangement is good. Just watch for turbulence and if you plan to use a dam, watch for standing waves.
    We have a small pipes test tank here at Unidata. It consists of a 150mm PVC pipe and submersible pump etc.
    We have been running these QSD’s down to a depth of about 60mm in this arrangement with no real problem.

    Q: What is the angle of the ultrasonic beam when using Starflow QSD to measure water level?

    Starflow QSD Water Level Beam Width

    A: Beam Width is 3.5° (-3dB point)

    Q: What is the angle of the acoustic beam with or spread when using Starflow QSD to measure the flow rate?
    What is the angle of the centreline of an acoustic beam?

    Varying Angle as Particles Pass Through the Main Beam

    A: The acoustic beam has a width, or spread, of about 10°. The centreline of the beam is aligned at 30° above horizontal but as a particle passes horizontally through, the actual angle within the beam varies from 25° to 35°

    Q: Will water level measurements be affected if ultrasonic touches the wall of the pipe?

    Starflow QSD Water Level Measurement in the Pipe

    A: The Starflow QSD should not be affected by the depth signal reflecting of the tube wall. This will cause a “smudging” of the return signal, but Starflow QSD detects the first pulse and ignores subsequent returns due to multi-path reflection.

    Q: The Starflow QSD is used in the water channel. The water level and flow rates can suddenly change.
    What is response time to depth change?

    A: Response time to depth change is controlled by the amount of the filtering/averaging being used. If no averaging is used, the depth measurement will be immediate depth value at the time of measurement. The response time is then determined by the rate of SDI-12 interrogation.
    Averaging is used in open water conditions to smooth out the effect of surface ripples/waves.

    Q: A customer wants to use a 6527A with their logger on a power cycle rather than continuously powered. Is this advisable, and if yes, how long should a QSD be powered in order to obtain proper readings, please?

    A: The QSD should power up quite quickly say around 2 seconds. Therefore you can issue the command to read the SDI-12 channel after this 2-second startup. If your log times are short then the QSD should be given at least 2 seconds to wake up and settle. You might like to give it up to 5 seconds if your log times are long i.e. 10 minutes and above. There should be no problem constantly powering up and then powering down the instrument.
    The instrument is normally asleep when it is not taking a measurement or talking on the SDI-12 bus. During these sleep periods, the QSD draws very little current.