Campbell Hydrosense, Инструкция по эксплуатации

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HydroSense
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making it possible to relate water content to measured dielectric permittivity.
Additionally, water and air are the only soil constituents that change with time.
The electronics embedded in the probe body generate the high frequency
electromagnetic energy necessary to polarize water molecules to the extent
needed to measure the dielectric permittivity. The travel time of
electromagnetic energy along a waveguide is dependent on the dielectric
permittivity. The probe rods act as a waveguide and the applied signal travels
to the end of the rods and reverses the direction of travel. Electronics
encapsulated in the probe head both generate the applied signal and sense the
return. The measurement reflects the average water content over the length of
the rods. The high frequency signals are transformed to a square wave output
with a frequency proportional to the water content. The HydroSense display
unit converts the output of the probe to a readout which gives information about
volumetric water content. The display output can be configured to display
volumetric water content or a deficit value derived from the present measured
value and reference levels previously determined.
The HydroSense is operated in the Water Content Measurement Mode or the
Water Deficit Mode . The mode is easily changed by holding down the
MENU button while pressing the READ button when the HydroSense is in the
sleep mode. The HydroSense automatically goes into sleep mode if either of
the buttons are not pressed for about 2 minutes. Pressing only the READ
button starts HydroSense in the last mode selected.
The Water Content Measurement Mode applies calibration coefficients to
the output of the probe to give volumetric water content in percent. The
calibration coefficients reside in the operating system and were determined by
the manufacturer. The amount of pore space in a typical soil is about 50%.
The pore space can be occupied by water in liquid or vapor phase or by air.
The other 50% of the soil is the solid portion. If the soil is saturated, that is, all
the pore space is filled with water, the water content is 50%. Volumetric water
content is defined as the volume of water per volume of soil.
In the Water Deficit Mode upper and lower reference measurement levels are
combined with the present measurement to provide relative water content
information and the amount of water that must be added to bring the water
content back to the upper reference value. Reference levels for up to 5 sites can
be stored in the HydroSense. Use of this mode requires the user take
measurements with the HydroSense when the soil is at the chosen upper and
lower reference levels and store the value. The reference levels might
correspond to the minimum desired water content for a crop and the water
content desired after irrigation. A value of 50 indicates the actual water content
is halfway between the reference levels and the value will be 100 after an
irrigation to the upper reference value.