Theta Probe ML3


The Theta Probe is well known as one of the most accurate and reliable soil moisture sensors on the market. The Model ML3 replaces the ML2x.


  • ±1% accuracy
  • New extendable cable system
  • New white body - reduces radiative heating
  • Improved calibration for soil salinity
  • Built in temperature measurement when buried
  • Dual purpose: either hand-held for spot readings or left in-situ for data logging


With the ThetaProbe Soil Moisture Sensor it's easy to make reliable, accurate soil moisture measurements. Simply insert the soil moisture probe into the soil, connect to your data logger or readout unit, provide 5-15V DC at 20mA, and within seconds you can be logging soil moisture.

ThetaProbe Soil Moisture Sensors are robust, buriable and maintenance free. They can be easily installed at depth in the soil by inserting them into augered holes using the optional extension tubes.

ML3 improvements
The addition of a thermistor sensor enables the simultaneous logging of soil temperature with soil moisture.

A new cabling system makes it simple to extend or replace cables. With a choice of 1m, 5m, 10m and 25m extensions, flexible configurations are now possible.

The ML3's salinity response has also been improved - its output has been characterised at EC values up to 2000 mS.m-1. The temperature range has also been improved - allowing operation at temperatures as low as -40 degrees C (non-flexing cables).


Sensors can be purchased individually for integration into datalogging systems, or used as part of a portable kit. The portable kit contains all the items needed to make rapid spot readings of soil moisture content with a ThetaProbe. The ThetaKit includes an HH2 Soil Moisture Meter readout unit, spare ThetaProbe rods, insertion kit and carrying case.


  • irrigation
  • hydrology
  • civil engineering
  • soil water profiling
  • pollution monitoring
  • forestry.

About the manufacturer

Delta-T specialise in manufacturing instruments for plant science and related studies.

Products include soil moisture sensors, stomatal conductance, canopy analysis system and solar radiation.


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