Delta-T Devices Ltd.

- Model WET-2 - Soil water content sensor, temperature sensor and pore water conductivity sensor (WET Sensor)


Measures Water content, EC and Temperature. Measures directly within the root zone. A vital tool for precision horticulture. In just 5 seconds the WET Sensor checks 3 crucial variables that influence plant growth: water content, temperature and pore water conductivity (ECp), the EC of the water that is available to the plant.

  • Moisture and nutrient status in the root zone
  • Rapid monitoring of growing conditions
  • Calibrations for many soils and substrates

The sensor is easily inserted into substrates, composts and most soils. It takes less than 5 seconds to measure water content (%), pore water conductivity (ECp) and temperature – all being important indictors of root zone health.

The WET Sensor is able to calculate pore water conductivity (ECp) which is the EC of the water available to plant roots. The ECp calculation is derived from an approximate relationship between dielectric properties. This applies particularly well to WET Sensor readings, which are taken at the same frequency within the same defined region of soil/substrate. The approximation is valid in most soils and is particularly accurate in mineral wool and other artificial substrates media.

Where plants are grown in artificial substrates using hydroponic or fertigation systems, nutrients are routinely supplied in irrigation water. Nutrient levels are controlled by monitoring the water content and conductivity (EC) and adjusting the injection of liquid fertiliser into the irrigation water. The Delta-T Devices WET Sensor excels in monitoring this crucial information.

Nutrients are sometimes provided by fertigation but are often provided by Controlled Release Fertilisers (CRF). The rate at which these are taken up depends on several factors, includingthe weather conditions and irrigation regime.

The Delta-T Devices WET Sensor can be used to measure the EC within the growing media and so take much of the guesswork out of this process.


If the irrigation water is recycled or abstracted from rivers and aquiferswith high levels of dissolved salts, over time there can be a build up of soil salinity. Soil salinisation will eventually reduce crop yields. The WET Sensor is fast and efficient for sampling soil salinity, ensuring that farmers have the essential information they need to take remedial action as quickly as possible.


WET Sensors are normally ordered as a complete kit that includes a WET Sensor, an HH2 Moisture Meter and a handy carry case. There are three types of Kit – each with a different set of substrate calibrations.


For portable applications, readout and data storage are handled by the HH2 Moisture Meter. Alternatively, the WET Sensor can be connected to the GP1 Data Logger or GP2 Data Logger and Controller, making it possible to monitor growing conditions over a period of hours, days or longer. The smart relay capability in these data loggers allows them to control water content in response to EC or temperature.

The WET Sensor is supplied with calibrations for generid mineral, organic, sand and clay soils. Special substrate calibrations can be ordered as a set for a variety of horticultural substates which are factory installed at Delta-T Devices.

  • WET-GH-1 for coir (coco fibre), peat based potting mixes, greenhouse ‘mineral’ soils
  • WET-ST-1 for Stonewoll artifical mineral wool substrate (vertical and hrizontal measurement)

Measured parameters

  • Permittivity, ε′: 1 to 80 ± 2.5 [1]
  • Bulk conductivity: 0 to 300 mS.m-1 ± 10 (ECb)
  • Temperature: -5 to 50°C ± 1.5°C

Calculated parameters

  • Volumetric Soil Moisture, θ: 0 to 100% ± 3% [2]
  • Pore water conductivity: see graph below (ECp)

Other specifications

  • Calibration: Individual sensor calibrations stored within sensor EEPROM
  • Output: Serial data (TTL)
  • Environmental: IP68, 0 to 50°C
  • Power: 6 to 10V, ~38mA for 2.5s
  • Dimensions: ~120 x 45 x 13mm
  • Rods: ~68mm long
  • Sample volume: ~500ml

[1] Permittivity is a measure of the dielectric properties of materials, e.g. soils and substrates.
[2] Soil moisture accuracy refers to errors after applying a soil-specific calibration, within 10°C of calibration temperature.