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Tensiometers Then and Now

Tensiometers Then and Now. Elizabeth Scherling BAE 558 Semester Project Spring 2005. Outline. Theory Components Historical Devices Applications Modern Devices Applications Calibration Maintenance Challenges Future Tensiometers. Theory.

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Tensiometers Then and Now

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  1. TensiometersThen and Now Elizabeth Scherling BAE 558 Semester Project Spring 2005

  2. Outline • Theory • Components • Historical Devices • Applications • Modern Devices • Applications • Calibration • Maintenance • Challenges • Future Tensiometers

  3. Theory • Tensiometers directly measure soil water matric potential • Forces responsible for capillary action and water retention • van der Waals • Electrostatic dipole • Osmotic forces • Surface tension

  4. Components I • Thin-walled porous cup • Rigid body • Pressure gauge • Mechanical • Electrical: pressure transducer • Hydraulic: manometer • De-aired water

  5. Components II Porous Cup Body Pressure Gauge

  6. Historical Devices I • B. E. Livingston • 1908 • Earliest account of a tensiometer-like device

  7. Historical Devices II • H. E. Pulling and B. E. Livingston • 1915 • Measured what they called the “water supplying power of the soil”

  8. Historical Devices III • C. J. Lynde and H. A. Dupre • 1913 • First hanging column design • Measured what they called the “capillary lift of soil”

  9. Historical Applications • Irrigation control • Auto-irrigation for potted plants • Capillary pressure measurement

  10. Modern Devices I • J. M. Hubbell and J. B. Sisson • 1998 • Advanced tensiometer design

  11. Modern Devices II • B. Lebeau, S. Barrington, and R. Bonnell • 2003 • Micro-tensiometer

  12. Modern Applications • Irrigation Control • Greenhouse • Farm • Field • Vadose Zone Studies • Transport Research • Ultimately: Tensiometers have the potential to save water and reduce infiltration contamination

  13. Calibration • The tensiometer must be subjected to known positive and negative pressures. • U-tube manometer • Vacuum chamber • Recalibration only recommended after long periods of inactivity.

  14. Maintenance • Gas Evolution • De-air water prior to filling and for subsequent water replacement • Vacuum, autoclave, or boil • Check for bubbles frequently in simple designs • Add water regularly for advanced designs • Maintain intimate contact between porous cup wall and soil matrix

  15. Challenges I Choosing the correct tensiometer Hubbell and Sisson, 1998

  16. Challenges II Weather Conditions Cloudy day Sunny day Hansen and Pasian, 1999

  17. Challenges III Limited Matric Potential Ranges • Low range: 3 to 6 kPa • Controlled and reliable • Medium range: 9 to 12 kPa • Not stable or reliable • High range: 15 to 18 kPa • Not stable or reliable From a study by Hansen and Pasian, 1999 Low Range Medium Range High Range

  18. Future Tensiometers • For long duration in situ use: • Cost effective advanced tensiometers • For large-scale greenhouse use: • Micro-tensiometers with greater control of large ranges of moisture tension

  19. Questions ?

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