Soil Moisture Brochure

The Science Behind HydraProbe

RELIABLE Continual, long-term data without calibration. y y Stable—no sensor drift, ensuring continual accuracy. y y Patented technology that accurately measures moisture and bulk electrical conductivity permits more accurate optimization of watering and fertilization than with just moisture. y y Depended on by the USDA, NOAA, leading irrigation companies, and many universities for over 20 years. Used by the USDA Soil Climate Analysis Network for ground truthing of satellite-based soil imaging. y y Soil moisture calibration has been rigorously peer-reviewed, making it one of the most trusted soil sensors available . RUGGED Durable stainless steel tines, fully potted components, compact sealed design and a 5-year warranty . y y Can remain in-situ indefinitely, or relocated and redeployed without worry. y y Ideal for remote locations, harsh environments and applications where data is critical. y y Enables measurement of native (undisturbed) soil, even hard- packed clay. y y Industry-leading 5-year warranty. SIMPLE Set it and forget it. y y Repeatable accuracy and stability without the need for calibration in most soils. y y Digital sensor using the SDI-12 or RS485 protocol—no setup, just connect to data logger. Compatible with any SDI-12/RS485 capable data logger. y y Zero maintenance required. ACCURATE Consistent research-grade accuracy every season, every location. y y Unparalleled spatial and temporal measurement consistency. No sensor-to-sensor variations across locations, seasons, soil types or moisture range. y y Instant measurement of the 3 most significant soil parameters simultaneously. y y Unlike most TDR or capacitance- based sensors, HydraProbe is less sensitive to changes in temperature, salinity, and soil mineralogy.

The HydraProbe’s “dielectric impedance” measurement principle differs from TDR, capacitance, and frequency soil sensors by taking into account the energy storage and energy loss across the soil area using a 50 MHz radio frequency wave. Unlike other soil sensors, this unique, patented method separates the energy storage (real dielectric permittivity) from the energy losses (imaginary dielectric permittivity). The HydraProbe’s detailed mathematical and signal characterization of the dielectric spectrum helps factor out errors in the soil moisture measurement such as temperature effects, errors due to salinity, and soil type. This method has passed the most rigorous scientific peer review from dozens of journals such as the Vadose Zone Journal, American Geophysical Union, and The Journal of Soil Science Society of America.





Real dielectric permittivity (isolated) Soil moisture for inorganic & mineral soil Bulk electrical conductivity Temperature**

< ± 0.5% or ± 0.2 dielectric units 1 to 80 where 1 = air, 80 = distilled water


± 0.01 WFV for most soils ± ≤0.03 max for fine textured soils* ± 2.0% or 0.02 S/mwhichever is typically greater*

From completely dry to fully saturated (from 0% to 100% of saturation)


0 to 1.5 S/m


± 0.3° C

-10°C to +60° C

0.1°C | | Tel: +44 (0) 1428 661 660

Inter-sensor variability

± 0.012 WFV ( θ m 3 m -3 )


* Accuracy may vary with some soil textures. ** Extended temperature range sensor (down to -40° C) available


Read-Out Options vanwalt DataHub


Power supply

9-20 VDC

9-20 VDC

Power consumption

<1 mA idle / 10 mA active 3-wire: power, ground, data

<10 mA idle / 30 mA active


4-wire: power, ground, com+, com- 1,219 m (4,000 ft.) Non-spliced: 304.8 m (1,000 ft.)

Max. cable length

60 m (197 ft.)

Baud Rate



A self powered, flexible system of electronics, conveniently packaged in an IP rated, heavy duty aluminium enclosure which performs as a hub to collect data from sensors. It organises the data for distribution or sharing through on- board memory, radio frequency, GPRS or satellite portals. vanwalt DataSlave The vanwalt DataSlave sits at the location of your monitoring – a field; well-head; arable land plot; stream, river or lakeside site – communicating between your deployed sensors to either the vanwalt DataHub or your laptop using radio waves. This sophisticated unit with a range up to 10 km line-of-sight, requires little power to act as an invisible wire linking SDI-12, Modbus or Pulse sensors to our telemetered data collection system. HydraGO Field Version Wireless, sensor-to-smartphone interface for HydraProbe. Features a rugged, anodized aluminum housing that contains a rechargeable battery that powers the connected HydraProbe and built-in ad-hoc Wi-Fi radio. The app will display soil moisture content, temperature, conductivity and dielectric permittivity on-screen for immediate viewing.

Communication protocol

SDI-12 Standard v. 1.2

Custom or open spec

Serial; allows multiple sensors to be connected to any RS485 or SDI-12 data logger via a single cable.





4.9” (124 mm)

y y Standard temperature probe range: -10°C to +60°C y y Standard Extended temperature probe range: -30°C to +60°C y y Extra Extended temperature probe range: -40°C to +65°C

1.6” (42 mm). Optional slim housing version available: 1.4” (35.8 mm) 7 oz. (200 g). Optional slim housing version available: 6.5 oz. (184 g)

Operating Temperature



Storage Temperature

-40°C to +65°C

Cable weight 0.86 oz/ft (80g/m) Sensing volume (cylindrical region) Length: 2.2” (5.7 cm) Diameter: 1.2” (3.0 cm)

Water Resistance

Tolerates continuous full immersion

18 gauge (20 gauge for RS-485/ analog), UV resistant, direct burial Excellent; potted components in PVC housing and 304 grade stainless steel tines


Vibration and shock resistance

* Accuracy may vary with some soil textures.

The HydraProbe is a rugged soil sensor with patented technology that provides continual, consistent accuracy to measure the three most significant soil parameters simultaneously - moisture, salinity and temperature.

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