ML3 ThetaProbe Soil Moisture Sensor

    How to Buy
thetaprobe, ml3-1 Zoom


"We have ThetaProbe sensors installed at another site, some of them have been running for 8 years now and we've found them very reliable, so we'd like to use Delta-T Devices sensors again." Anu Riikonen, PHD Student
Department of Forest Ecology, University of Helsinki
  • 5-year-warrantyClass leading ± 1% soil moisture accuracy
  • Can be buried or used as portable probe
  • Easy data logger connection (0 – 1V DC)

With its 1% accuracy the ThetaProbe has set the standard for soil moisture measurement for more than 20 years.

Highly accurate yet easy to use

With the ML3 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.

The ML3 ThetaProbe is robust, buriable and maintenance free (environmentally protected to IP68). It can be easily installed at depth into augered holes using the optional extension tubes.

The ML3’s excellent salinity response has been characterised at EC values up to 2000 mS.m-1. It also has a wide operating temperature range, allowing it to be used at temperatures as low as -40 degrees C (non-flexing cables).

The ML3 includes a thermistor sensor for the measurement of soil temperature of soil temperature with soil moisture (probe must be fully buried).

Data logging and readout

The ML3 can be logged by any Delta-T data logger; it is compatible with any logger that can provide 5 – 15V DC excitation power and will accept the 0 – 1V output signal. For portable applications the ML3 connects to the HH2 Moisture Meter and they can be ordered together as the convenient ThetaKit – see below (please note that the HH2 Meter does not provide temperature readings).

Easy installation

The ML3 ThetaProbe is buriable and its cylindrical shape makes it easy to install in augered holes (45mm diameter). The tough stainless steel rods can be replaced if bent or damaged. The threaded base of the sensor can be connected to optional 50cm and 100cm extension tubes.


Typical applications include irrigation, hydrology, civil engineering, soil water profiling, pollution monitoring and forestry. Because the ThetaProbe has a predictable saline response (which actually declines as salinity increases) it can be used even in very saline soils – up to 2000 mS.m-1.

The ThetaProbe can also be used in non-soil media.

ThetaKitThe ML3 ThetaKit

Supplied in a convenient carry case, the ThetaKit contains everything needed to makes accurate spot readings of soil moisture content. The kit comes complete with a dedicated HH2 Moisture Meter for instant readout, an insertion tool for penetrating hard soils, and a set of spare replacement rods.

ThetaKits are an excellent choice for turf grass applications

Please not that the HH2 Meter does not provide temperature readout or recording.


 Water content
Accuracy ±0.01 m3.m-3   (1%)
Range 0 to 0.5 m3.m-3
Salinity range 50 to 500 mS.m-1
< 0.035 m3.m-3
Accuracy ± 0.5°C, 0 to +40°C
± 0.75°C, -20 to +60°C [1]
 Output                      0 to 1.0V differential
 Power  5 to 14V, 18mA for 1s
 Sample vol.  Approximately 60 x 30mm diameter
 Overall size  170 x 40mm diameter
 Environmental  IP68, -40 to +70°C


[1] Figures apply to sensor only and exclude logger or cabling errors


For more detailed ML3 specifications see Soil Moisture Measurement Catalogue



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