Campbell Scientific HS2 and HS2P (HydroSense II) - Manual (Page 16)

HS2 and HS2P
5.3.1 Height
Handle to bottom of sensor: 82.3 cm (32.4 in)
Top of display to
bottom of sensor: 96.5 cm (38 in)
5.3.2 Weight
With display and sensor: 1.4 kg (3 lb)
Without display: 1.1 kg (2.4 lb)
6. Operation
6.1 Assembly and First Use
This information is provided in Section 3, Quickstart .
6.2 Measurements
The HydroSense II presents two distinct data sets. One data set includes
volumetric water content expressed as percent (%) and period (μs). The second
data set includes an estimate of relative water content relative to pre-measured
wet and dry references, and water deficit. Water deficit provides an estimate of
applied water required (in mm) to return the soil to the “wet” water content.
By default, only water content data are displayed. Using the configuration
menu (p. A-1), water deficit data can be enabled to display side-by-side with
water content data.
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 (labeled “VWC” on the
display) and period (labeled “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.
NOTE
8