Delta OHM: Probes for soil volumetric water content measurement

Delta OHM HD3910.1 &HD3910.2



• Measurement of the soil volumetric water content with
2 electrodes (HD3910.1) or 3 electrodes (HD3910.2)
for restricted volumes
• Measurement of the soil temperature
• Various output options available (depending on model):
digital RS485 with MODBUS-RTU protocol, digital
SDI-12 or analog voltage
• Accurate and stable measure over time
• Degree of protection IP 67
• Minimal invasiveness in the soil
• Easy to install

The probes HD3910.1 (two electrodes) and HD3910.2 (three electrodes) measure the soil volumetric water content (VWC) by using a capacitive measurement principle which allows fast measurements in the field and with minimal invasiveness. The three electrode probe HD3910.2 is particularly suitable for the measurement in small volumes, for example for cultivations in pots.

The moist soil is composed of a solid part (minerals), a liquid part (generally water) and a
gaseous part (air, water vapor).
The Volumetric Water Content (VWC) is defined as the ratio between the volume occupied by
the water (Vw) in a certain portion of the soil and the total volume of the soil portion (V):

VWC=Vw / V

It can also be expressed as a percentage (% VWC) of the water volume in the total volume.

The volumetric water content is a parameter used in hydrology for the study of the hydraulic
properties of the soil, and in agriculture to determine the need to irrigate crops.


  • Measuring principle : Capacitive
  • Measuring range: 0…60% VWC
  • Resolution:0.1%
  • Accuracy (@ 23 °C) ± 3 % between 0 and 50% VWC (standard mineral soil, EC < 5 mS/cm)
  • Sensor operating temperature:-40…+60°C
  • Power supply
    • Versions with RS485 output:
    • 2 mA average / 15 mA peak @ 12 Vdc Versions with analog output:
    • 2.5 mA average / 15 mA peak @ 12 Vdc Versions with SDI-12 output:
    • 300 µA @ 12 Vdc in standby <15 mA @ 12 Vdc during measurement
  • Materials : Handle: thermoplastic material and epoxy resin/Electrodes: epoxy glass, thickness 2 mm
  • Protection degreeIP 67




By means of an accessory, perform a hole into the soil deep enough to accommodate the probe. Never use the probe to make the hole in the soil, in order to avoid mechanical damage to the probe itself.
Once the hole was done, insert the probe completely into the soil so that the entire handle is covered by the ground: the temperature sensor is located inside the handle, close to the electrodes; therefore, it is necessary that the handle is immersed in the soil for a correct detection of the temperature.
After the introduction of the probe, fill in the empty spaces between the soil and the probe with some soil made powder. To obtain accurate measurements, the soil should be in contact with the electrodes and the probe handle.

Ordering Codes


(1) Probe type

CodeProbe type
Probe type

(2) Out Put Type

CodeOutput Type
RS485 Modbus-RTU output
SSDI-12 output
A0.5…3 V analog output (other ranges on request)
Output Type

(3) Cable Length

CodeCable Length
Cable length

Soil Volumetric Water Content Detector
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