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.
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.
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 permitivities—the key parameters behind the soil moisture and bulk EC measurement.
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.
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 |
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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 |
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| 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 |
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| 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) | ||
PART # | DESCRIPTION |
|---|---|
| 56012-02 / 56485-02 / 56585-02 | HydraProbe ( Professional ) with 25’ (7.62 m) cable, SDI-12 / RS-485 / Modbus |
| 56012-04 / 56485-04 / 56585-04 | HydraProbe ( Professional ) with 50’ (15.24 m) of cable, SDI-12 / RS-485 / Modbus |
| 56012-06 / 56485-06 / 56585-06 | HydraProbe ( Professional ) with 100’ (30.48 m) of cable, SDI-12 / RS-485 / Modbus |
| 56000-TST | Temperature Test Certificate |
