Delta-T Devices Ltd.

- Model EQ3 - Equitensiometer


The EQ3 uses class leading ThetaProbe technology to avoid the many problems of water-filled tensiometers. It measures water potential (matric potential) in the range 0 to -1000 kPa and provides an accurate loggable output. It is particularly well suited for use in dry soils.

  • Convenient, accurate and reliable alternative to water-filled tensiometers 
  • Excellent range 0 to -1000 kPa
  • Maintenance free: no refilling, degassing, or topping up
  • Built in temperature sensor
  • Buriable and frost resistant (IP68)


The EQ3 Equitensiometer offers maintenance-free operation over a wide soil water potential range. It provides reliable matric potential measurements as well as soil temperature.

The EQ3s measuring rods are embedded in a porous material (the equilibrium body). This material has a known, stable relationship between water content and matric potential. When the EQ3 is inserted into the soil, the matric potential within the equilibrium body equilibrates to that of the surrounding soils. The water content of the matric material is measured directly by the EQ3, and this can be converted into the matric potential of the surrounding soil using the calibration curve supplied with each Equitensiometer.

Installation and usage
The EQ3 is buriable (IP68) and maintenance-free. It can be inserted into augured holes or positioned in the wall of a trench (which is then carefully back-filled). Optional extension tubes assist placement and removal when burying at depth.

The EQ3 is rugged, maintenance-free (no refilling, degassing, or topping up required), frost resistant and low powered; this means it can left installed at remote sites over long periods of time. In such instances it is possible to access sensor data wirelessly via a GPRS enabled data logger such as the Delta-T GP2.

Please note that despite its many strengths, the EQ3 should not be seen as a rapid response sensor that covers the full range of water potentials at high accuracy. Such a sensor does not yet exist. EQ3 equilibration time is typically several hours.


The EQ3 Equitensiometer is ideally suited to static long term monitoring of water potential in soils and substrates. It can even be left installed in frozen soils. Typical applications include environmental, plant, soil, ecology and geo-sciences research, as well as civil engineering and agricultural engineering applications.

The EQ3's full range is 0 to -1000 kPa but best accuracy is achieved between -100 and -500 kPa. This makes it well suited to plant water stress studies - even in very dry soils.

Data logging
The EQ3 can be logged by any Delta-T data logger, including the powerful GP2. It is also compatible with many other manufacturers' data loggers. The EQ3 can also be used with an HH2 Moisture Meter, but only the unconverted millivolt output is displayed, and the temperature reading is not available.

Matric Potential

  • Accuracy: ±10kPa over 0 to -100kPa, ±5% of reading over -100 to -1000kPa
  • Measurement range: 0 to-1000kPa (-10bar)
  • Hysteresis: Not detectable if the change of matric potential is slower than 0.1kPa/min
  • Soil types: Suitable for all non-saline soil types
  • Output signal: 0-1V differential, non-linear. (Calibration data and graph supplied with each sensor)
  • Output compatible with:: GP1, GP2, DL6, DL2e, HH2

Temperature (EQ3 must be fully buried to accurately measure soil temp)

  • Sensor accuracy: ±0.5°C over 0-40°C not including logger or cabling error
  • Output: Resistance: 5.8kΩ to 28kΩ
  • Output compatible with:: GP1, GP2, DL6 [1]1, DL2e, HH2
  • Cabling error contribution (for temperature readings):
    • Negligible for GP1, GP2 & DL6 (100m cable limit)
    • Negligible for DL2e (with 5m cable) [2]
  • Max cable length:
    • 100m (GP1, GP2 & DL6 data loggers)
    • 100m (DL2e: water content measurement)
    • 25m (DL2e: temperature measurement)
  • Power requirement: 5 to 15V, 20mA for 1s
  • Operating range: -0 to +40°C (Not damaged by use in frozen soils)
  • Environmental: IP68
  • Dimensions/weight: 181mm x 40.5mm dia./260 gm (without cable)

[1] Note: The DL6 has only one temperature channel. The DL6 error contribution to EQ3 temperature measurement is negligible compared to the accuracy of the EQ3 temperature sensor itself. The two only become comparable below -15C.
[2] DL2e Logger users can apply a correction in the Ls2Win logging software (for cable lengths >5m).