Manual – Starflow QSD Model 6527B and 6537A
Unidata Manual - 6527B and 6537A Starflow QSD User Manual 08 05 2023.docx
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4.2
Water Depth Measurement – Ultrasonic
For depth measurement, the Starflow QSD uses Time-of-Flight (ToF) Ranging. This involves
transmitting a burst of ultrasonic signal upwards to the surface of the water and measuring
the time taken for the echo from the surface to be received by the instrument. The distance
(water depth) is proportional to the transit time and the speed of sound in water (corrected
for temperature and density). The maximum ultrasonic depth measurement is limited to 5m.
The minimum ultrasonic depth is 40mm above the ultrasonic eye.
NOTE: If there is a large ripple on the surface of the water due to windy conditions, this may
cause erratic Ultrasonic depth readings as it will not be able to resolve the correct
reflections; in these cases, the Pressure depth sensor will need to be used.
4.3
Water Depth Measurement - Pressure
Sites where the water contains large amounts of debris or air bubbles, may be unsuited for
ultrasonic depth measurement. These sites are better suited to using pressure to determine
the water depth.
The pressure-based depth measurement may also be applicable to sites where the
instrument cannot be located on the floor of the flow channel or cannot be mounted
horizontally.
The Starflow QSD is fitted with a 2 bars absolute pressure sensor. The sensor is located on
the bottom face of the instrument and utilises a temperature-compensated digital pressure
sensing element.
Where depth pressure sensors are used, the atmospheric pressure variation will cause
errors in the indicated depth. This is corrected by subtracting the atmospheric pressure from
the measured depth pressure. A barometric pressure sensor is required to do this.
