QSD SDI-12 Flowmeter






  • SDI-12 compatible
  • Easy to use
  • Robust, reliable – completely sealed against water ingress
  • Inexpensive – to buy, install and operate
  • Easy to web-enable – with Neon telemetry data loggers
  • Easy to install – compact, will easily fit most structures
  • Low maintenance – no battery changes or calibration required
  • Low power consumption
  • Records Flow in streams, open channels and part-filled pipes.
  • Battery Powered for use in remote locations


The Starflow QSD SDI-12 Instrument is a simple, low-cost flow monitoring solution, suitable for use in a wide range of water qualities, from sewage to potable water and everything in between, including sea water. It uses the Ultrasonic Doppler Principle in Quadrature Sampling Mode to measure water velocity, transmitting 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 QSD’s ultrasonic receiver where the instrument processes this received signal and calculates the water velocity. 

Water depth is also measured with a built-in ultrasonic depth sensor which overcomes problems encountered with conventional pressure sensors, particularly their susceptibility to damage from water-borne debris. It also eliminates the need for frequent recalibration to maintain accuracy and does away withthe need for vented cable. 

The use of all-round ultrasonic technology allows the QSD instrument to be completely sealed. It is potted in a solid block of ‘ultrasonic-transparent’ epoxy, free from any potential leaks that might otherwise occur. The low-profile form-factor of the QSD minimises disturbance to the flow it is measuring. 

The QSD Instrument measures velocity in both directions and with a companion Unidata IP data logger may be programmed to compute flow rate and total flow in pipes and open channels of known dimensions.

Simply mount it on, or near the bottom of the water channel and you are ready to measure.


20mm/s to 1600mm/s in one direction (default)
20mm/s to 3200mm/s in one direction (parameter setting)
Bidirectional flow capability (parameter setting)

Accuracy: 2% of measured velocity
Resolution: 1mm/s

Range: 20mm to 2000mm – above sensor in water with heavy sediment
Range: 20mm to 5000mm – above sensor in water with medium sediment
Accuracy: Typical ±1%

Range: 0°C to 60°C
Resolution: 0.1°C

Voltage Range: 10 to 24V DC
Supply Current: 50uA standby, 100mA active for 1s
Power Source (typical): External battery 12V DC

SDI-12: Velocity, depth, temperature and diagnostic features
Connection: Single three-wire cable up to 50m long
Software: Compatible with Starlog V4

Operating Temp: 0°C to 60°C water temperature
Storage Temp: -20°C to 85°C
Humidity: 100%

Dimensions: L 135mm x W 50mm x H 20mm
Material: Epoxy-sealed body, stainless steel mounting plate
Weight: 200g
Cable: 15m, three wire
Cable Options: User specified length up to 50m