Water level - capacitive (Odyssey)

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Odyssey.jpg

Contents

Parameter to be measured:

Water level

Method:

Capacitive

Equipment:

Odyssey

Advantages:

  • Cheap
  • Logging of 64k of data
  • Logger start by starting start time
  • The lack of an outer shroud makes it easy to transport the probes
  • Available in different lengths
  • Available with 2 sizes of brass weights
  • The probe fits exactly on a 32 mm (ID) PVC pipe
  • You can replace the batteries yourself
  • Log-interval can be event-controlled
  • Very good support from the company (prompt answering emails).

Disadvantages:

  • Each sensor needs to be calibrated:

"median measurement error that ranged from 11 to 288 mm using the bucket calibration method and 12 to 81 mm using the PVC pipe calibration method" (Larson and Runyan, 2009)

  • the sensor is not compensated for temperature or electrical conductivity.
  • manufacture state the accuracy to be -+ 5mm, but in practice it tends to be -+1cm.
  • temperature dependency: "tests in water temperatures of 0°C - 20°C have shown a variation (under estimation) of approximately 5mm" (manufacture statement).
  • electrical conductivity dependency:
    • "If the conductivity of the water is above 5000µS/cm the sensor is largely unaffected by fluctuations in conductivity whereby large changes result in very small variations in the recorded data" (manufacture statement).
    • "We suggest these probes only be used in water higher in conductivity than 4150 μS/cm" (Larson and Runyan, 2009).
    • Larson and Runyan (2009) tested the influence of EC on the measurement by changing the EC. Here are the results (see study for details):
      • EC variations: from 590 μS/cm to 1600 μS/cm --> "observed" water level variations: 40 mm
      • EC variations: from 705 μS/cm to 1000 μS/cm --> "observed" water level variations: 15 mm
      • EC variations: from 670 μS/cm to 1200 μS/cm --> "observed" water level variations: 24 mm
      • EC variations: from 210 μS/cm to 620 μS/cm --> "observed" water level variations: 153 mm
      • EC variations: from 175 μS/cm to 1950 μS/cm --> "observed" water level variations: 240 mm

What to watch out for:

  • Don’t damage the wire.

Problems/Questions:

  • After 2 years of use, two of my loggers would no longer connect to the computer. All others still worked fined.
  • One of my loggers would only record data for a few seconds. Restarting the logger and letting it run until the storage was full seemed to take care of this.
  • How do temperature/electrical conductivity influence the measurement.

Price:

between 120 and 150 EURO (2010, Germany) depending on the length

Links

Projects that used the above equipment:

Other related web sites:

References

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