Valeport Ltd

- Model 801 - Electromagnetic Open Channel Flow Meter



This small solid-state sensor has been designed specifically for use in open channels where fouling by weed or sewage can be a problem. Valeport's experience in electromagnetic technology has ensured that the Model 801 is a high precision instrument which can be relied upon to give accurate readings (±0.5% of reading plus zero stability) over a wide flow range (±5 m/sec) in only 5cm of water. The control display unit provides a choice of averaging modes, standard deviation of the data, and an optional logging facility.

Model 801 - Cylindrical Type

  • Range: -5m/s to +5m/s
  • Accuracy: ±0.5% of reading plus 5mm/s
  • Zero Drift: <5mm/s
  • Sensing Volume: Sphere of approx 12cm diameter around sensor
  • Minimum Depth: 15cm

Model 801 - Flat Type

  • Range: -5m/s to +5m/s
  • Accuracy: ±0.5% of reading plus 5mm/s
  • Zero Drift: <5mm/s
  • Sensing Volume: Cylinder of approx 20mm Ø x 10mm high
  • Minimum Depth: 5cm

What’s the Difference?
The smaller sampling volume of the flat sensor makes it very much more suitable for shallow flows, or measurements in confined spaces. However, it is also very much more sensitive to turbulent flows, which may manifest as apparently noisy real time readings. This effect can be minimised by using a long (>30secs) average period. The larger sampling volume of the cylindrical sensor effectively eliminates the turbulence noise, but also means that a greater depth of water is required for measurements.

Data Acquisition
The Model 801 Flow Meters are supplied with a dedicated surface display unit, which both drives the sensor and provides data display of the measured water velocity.

Data is updated at 1Hz, and may be averaged over any number of seconds from 1 to 600. The display will show real time speed data at a resolution of 1mm/s, as well as the result of the data average, and a Standard Deviation figure to give added data confidence. A solid state memory records all results (up to 999 averaged readings), and the data may be downloaded to PC using the RS232 interface lead supplied.

Both instruments are calibrated to NAMAS traceable standards at Valeport’s own premises up to speeds of 1m/s. Higher speed measurements are based on linear extrapolation. Specific high speed calibrations can be arranged at a third party facility on request.

Display Unit

  • Size: 244mm x 163mm x 94mm, 2kg
  • Environmental: Sealed to IP67
  • Power: 8 x alkaline C cells, lasting for up to 37 hours
  • Operating Temp.: -5°C to +50°C (display unit)
  • -5°C to + 40°C (sensor)

Both instruments are available for use as hand held “Wading Sets” only, with the operator standing in the channel, holding the instrument in position. The system is supplied with 1.5m wading rod (3 x 0.5m sections), graduated in cm, and a 3m cable from instrument to display unit.

Alternatively, a “top-setting” wading rod system is available, which allows the vertical position of the instrument to be set without removing the wading rods from the water.

System is supplied with CDUExpress Windows based PC software, for data extraction from display unit. CDU Express is license free.

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