Campbell CS616 Manuel d'instructions télécharger pdf (Page 38)

CS616 and CS625 Water Content Reflectometers

10 15 20 25 30 35 40

Water Content = 30%

Water Content = 12%

Water Content Error with Temperature

Soil Temperature (C)

Water Content Error (%VWC)

FIGURE 7-4. Percent volumetric water content error corrected for by

temperature correction equation

8. Water Content Reflectometer User-Calibration

8.1 Signal Attenuation in Conductive Soils and Need for Site-

Specific Calibration

A shift in water content reflectometer response results if the applied signal is

attenuated significantly. There is a voltage potential between the probe rods

when a pulse is applied to them. If the material between the rods is electrically

conductive, a path for current flow exists and the applied signal is attenuated.

Since the parallel rod design in soil is inherently a lossy medium and

attenuation is frequency dependent, both the amplitude of the reflection and the

rise-time or bandwidth are affected. Instead of a relatively short rise-time

return pulse, the rise-time is greater and the amplitude is less.

The reflected signal must exceed a set amplitude before the next pulse is

triggered. Reflections that are attenuated and have longer rise-times will take

longer to be detected and trigger the next pulse leading to decreased frequency

or increased period in conductive materials.

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Campbell CS616 Manuel d'instructions Page 38