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HydraProbe soil moisture, temperature, and conductivity sensors

Updated:2025-03-13

Brand: Stevens
Model: HydraProbe
Description: Meet the HydraProbe?. A rugged soil sensor with patented technology to measure the three most significant soil parameters—moisture, electrical conductivity and temperature.?The HydraProbe? is the most
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Product Details

HydraProbe soil moisture, temperature, and conductivity sensors Description：

Datasheet

Meet the HydraProbe®. A rugged soil sensor with patented technology to measure the three most significant soil parameters—moisture, electrical conductivity and temperature.?The HydraProbe® is the most scientifically researched soil sensor available and is depended on by the USDA, NOAA, farmers, leading irrigation companies, and universities for over 25 years. It has been engineered to handle the terrain you want to measure and provides data you can trust year after year.

HydraProbe® was originally developed by the physics department at Dartmouth College. It’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). Complex mathematical computations performed by an onboard microprocessor process the reflected signal measurements to accurately determine the soil’s dielectric permittivities—the key parameters behind the soil moisture and bulk EC measurement.

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. Low inner-sensor variability means there is no need for sensor-specific calibrations.

Patented Sensor Technology

HydraProbe uses unique “Coaxial Impedance Dielectric Reflectometry” to provide consistent long-term accuracy of moisture, salinity and temperature in any soil type. This also provides low inter-sensor variability, so every sensor measures the same without the need to calibrate.

MOISTURE

SALINITY (BULK EC)

TEMPERATURE

REAL PERMITTIVITY

IMAGINARY PERMITTIVITY

PORE WATER EC

Reliable

Continual, long-term data without calibration.

Stable—no sensor drift, ensuring continual accuracy.

Patented technology that accurately measures moisture and electrical conductivity permits more accurate optimization of watering and fertilization than with just moisture.

Depended on by the USDA, NOAA, leading irrigation companies, and many universities for over 20 years. Used by NASA for ground truthing of satellite-based soil imaging.

Soil moisture calibration has been rigorously peer-reviewed, making it one of the most trusted soil sensors available.

Accurate

Consistent research-grade accuracy every season, every location.

Unparalleled spatial and temporal measurement consistency. No sensor-to-sensor variations across locations, seasons, soil types or moisture range.

Instant measurement of the 3 most significant soil parameters simultaneously—moisture, salinity and temperature.

Unlike most TDR or capacitance-based sensors, HydraProbe is less sensitive to changes in temperature, salinity, and soil mineralogy.

Simple

Forget calibrating, ignore the soil type. Just set it and forget it.

Repeatable accuracy and stability without the need for calibration in most soils.

Digital sensor using the SDI-12 protocol—no setup, just connect to data logger. Compatible with any SDI-12 capable data logger.

Zero maintenance required.

Rugged

Durable stainless steel tines, fully potted components and a 5-year warranty.

Can remain in-situ indefinitely, or relocated and redeployed without worry.

Ideal for remote locations, harsh environments and applications where data is critical.

Enables measurement of native (undisturbed) soil, even hard-packed clay.

Industry-leading 5-year warranty.

HydraProbe PROFESSIONAL

VWC (% Moisture)

Temperature (°C / °F)

Electrical Conductivity (EC)

Pore Water EC

Thermal compensation

5 standard soil calibrations

Custom calibrations can be programed into the sensor

5 year warranty

Operating temperature: 40°C to 75°C

Specifications

MEASUREMENT	ACCURACY	RANGE	RESOLUTION
Real dielectric permittivity (isolated)	± 0.5% or ± 0.2 dielectric units	1 to 80 where 1 = air, 80 = distilled water	0.001
Soil moisture for inorganic & mineral soil	± 0.01 WFV for most soils ± 0.03 max for fine textured soils*	From completely dry to fully saturated (from 0% to 100% of saturation)	0.001
Bulk electrical conductivity	± 2.0% or 0.02 S/m whichever is typically greater	0 to 1.5 S/m	0.001
Pore Water EC	N/A	must have > 0.10 wfv	0.001
Temperature	± 0.3°C	-40°C to +75°C	0.1°C
Inter-sensor variability	± 0.012 WFV (θ m³ m^-3)	n/a

ELECTRICAL AND COMMUNICATION
	SDI-12	RS-485	Modbus
Power supply	9-16 VDC	9-16 VDC	9-16 VDC
Power consumption	1 mA idle / 25 mA active	2.5 mA idle / 25 mA active	2.5 mA idle / 25 mA active
Cable	3-wire: power, ground, data	4-wire: power, ground, com+, com-	4-wire: power, ground, A, B
Max. cable length	60 m (197 ft.)	1,219 m (4,000 ft.)	1,219 m (4,000 ft.)
		Non-spliced: 304.8 m (1,000 ft.)	Non-spliced: 304.8 m (1,000 ft.)
Baud Rate	1200	9600	1200-115200 9600 (default)
Communication protocol	SDI-12 Standard v. 1.2	Custom or open spec	Modbus RTU

ENVIRONMENTAL
Operating temperature range	-40°C to +75°C**
Storage temperature range	-40°C to +75°C
Water resistance	Tolerates continuous full immersion
Cable	18 gauge (SDI-12) / 22 gauge (RS-485 and Modbus), UV resistant, direct burial
Vibration and shock resistance	Excellent; potted components in PVC housing and 304 grade stainless steel tines
* Accuracy may vary with some soil textures. ** Temperature Test Certificate from -40°C to 75°C available

PHYSICAL
Length	4.9” (124 mm)
Diameter	1.6” (42 mm)
Weight	7 oz. (200 g) Optional slim housing version available: 6.5 oz. (184 g)
Cable weight	0.86 oz/ft (80g/m)
Sensing volume	Length: 2.2” (5.7 cm)
(cylindrical region)	Diameter: 1.2” (3.0 cm)