Campbell HydroSense II HS2, Руководство по эксплуатации продукта

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HS2 and HS2P
9
6.3 Water Content Data
Volumetric water content (VWC) and period (PER) data are retrieved from the
sensor. The HydroSense II sensor uses a proprietary technique to determine
water content over widely varying soils while correcting for a range of bulk
electrical conductivities. Volumetric water content (label
l
ed “VWC” on the
display) and period (labe l led “PER” on the display) data are requested from
the sensor via SDI-12 serial protocol.
Soil consists of three main constituents – mineral particles (sand, loam, or
clay), water and air. Air and water occupy the spaces or pores formed between
the mineral particles. In agricultural soils, these pore spaces typically make up
approximately 50% of the soil by volume, with water and air together making
up the remaining 50%. As a result, water content normally ranges from 0% to
50%. In some conditions, the sensor is unable to determine the soil water
content. In these cases, an out-of-range symbol (---) is displayed.
Even when the sensor cannot determine the VWC, the signal
period measurement will always be displayed. In special media
this value can often be used with a soil specific calibration to
estimate water content.
6.4 Water Deficit Data
Water deficit data help irrigators with water management decisions. By default,
the HydroSense II does not show water deficit data on the display screen. To
enable the water deficit data display, turn on Deficit Mode in the configuration
menus
(p. A-1)
.
In water deficit mode, wet and dry references can be stored for up to ten soils.
The current measurement is compared to those reference values and relative
water content (RWC) is calculated on a scale from 0% (dry) to 100% (wet).
While any two volumetric water content measurements can be stored as “wet”
and “dry” references, the normal procedure is to store the wilting point as the
“dry” value and field capacity as “wet”. The relative water content is calculated
as
100
×
−
−
=
dry wet
dry
VWC VWC
VWC VWC
RWC
where
VWC = the current measurement
VWC
dry =
the dry reference
VWC
wet
= the wet reference.
For example, a particular clay-loam soil may reach wilting point at 18% and
field capacity at 35%. With these references, a VWC measurement of 24.5%
will display as a relative water content of 38.2%. A VWC of 30% is calculated
as an RWC of 70.6%.
NOTE