Product Description
The cable length can be extended to 1219m using RS485
Electrode Material Stainless Steel

Physical dimensions
1. Long: 4.9 in (12.4 cm)
Diameter: 1.6 in (4.2 cm)
2. Sensor (cylindrical area)
Long: 2.2 in (5.7 cm)
Diameter: 1.2 in (3.0 cm)
3. Heavy: 200 g (cable: 0.08 kg/m)

　 Principle of Soil Moisture Salt Temperature Sensor:

The unique measurement method of Hydra Probe makes it more accurate and reliable in most soils compared to other sensors. The soil moisture calibration curve of electronic soil sensors is based on their composite dielectric constant (Topp 1980).

Composite dielectric constant is the ability of a material to generate induced charges in an electric field. When electromagnetic waves propagate through soil, some energy is stored while another part is lost. The mathematical relationship between the lost energy and the stored energy is not fixed.

The real part that reflects the energy storage or capacitance characteristics is directly related to the rotational dipole moment of water (Logsdon 2005, Seyfried 2004), and this principle is used for measuring soil moisture. The imaginary part represents energy loss, including conductivity, frequency, molecular relaxation, etc. (Hilhorst 2000).

The apparent dielectric constant is a complex dielectric constant of a dielectric material that includes both real and imaginary parts (Jones 2005, Seyfried 2007). Except for Hydra Probe, most sensors use measurement methods such as TDR (Blonquist 2005), TDT (Blonquist 2005B), RF resonant frequency capacitance method (Kelleners 2004), and SIP simplified impedance probe method (Gaskin 1996), all of which are based on apparent dielectric constant. The imaginary part of the dielectric constant is highly sensitive to conditions such as temperature, frequency, soil salinity, and soil texture. Therefore, the apparent dielectric constant, which includes the characteristics of the imaginary part of the dielectric constant, is also sensitive to temperature, frequency, soil salinity, and soil texture (Blonquist 2005).

Given that most soil sensors calculate soil moisture based on the apparent dielectric constant rather than the actual dielectric constant (real part), these sensors are severely affected by soil temperature, salinity, and texture. In contrast, Hydra Probe is less affected by soil conditions.

Hydra Probe is a dielectric impedance sensor that utilizes a coaxial waveguide to perfectly separate the real and imaginary parts (Campbell 1990). By using a transmission signal and two reflection signals, the impedance of the two reflection signals corresponding to the real and imaginary parts of the dielectric constant is different, and they are calculated separately through a mathematical model of Maxwell's equations (Campbell 1988, Kraft 1987). These complex mathematical calculations are carried out by a microprocessor built into the Hydra Probe casing.

Sensor calibration

As mentioned earlier, the calibration of Hydra Probe is based on the actual dielectric constant, rather than the apparent dielectric constant used by other sensors, making it more accurate and reliable than other sensors. LOAM soil calibration is the primary soil calibration performed by Hydra Probe and is suitable for most soil measurements. The calibration of LOAM loam soil is based on M. from the US Department of Agriculture S. Seyfried's research (Seyfried 2005). A series of soils representing different textures, morphologies, and mineral contents were studied to provide the best calibration curves for soil moisture measurement.

At the same time, Hydra Probe also performed calibration on sandy soil, clay, and sub clay; If necessary, customers can also calibrate according to their specific area requirements.