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ML3 ThetaProbe Soil Moisture Sensor

Updated:2023-04-28

Brand: Delta-T
Model: ML3
Description: With its 1% accuracy the ThetaProbe has set the standard for soil moisture measurement for more than 20 years.
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Product Details

ML3 ThetaProbe Soil Moisture Sensor Description：

User's Manual Getting Started Guide

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 5-14 V DC at 18 mA, 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 ºC (non-flexing cables).

The ML3 includes a thermistor sensor for the measurement of soil temperature (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 – 15 V DC excitation power and will accept the 0 – 1 V 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 (45 mm diameter). The tough stainless steel rods can be replaced if bent or damaged. The threaded base of the sensor can be connected to optional 50 cm and 100 cm extension tubes.

Applications

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.

Feature

Class leading ± 1% soil moisture accuracy

Can be buried or used as portable probe

Easy data logger connection (0 – 1 V DC)

ML3 ThetaProbe Soil Moisture Sensor Specification：

Measurement	Volumetric water content and soil temperature
Accuracy	± 0.01 m ₃ .m _-3(1%) With soil-specific calibration
Accuracy	± 0.5°C (0 to 40°C for temp sensor) ± 0.75°C (-20 to +60°C for temp sensor)
Soil moisture measurement range	Full accuracy over: 0 to 0.5 m ₃ .m _-3
Soil moisture measurement range	Full range : 0 to 1.0₃ .m _-3
Salinity range	50 to 500 mS.m _-1
Salinity range	Salinity errors < 0.035 m3.m-3 from 0.05 to 0.4 m₃.m_-3. Can be calibrated up to 2000 mS.m_-1
Temperature range	Full accuracy over: 0 to 40°C
Output	0 to 1.0 V differential Corresponding to 0 to ~0.6 m ₃ .m _-3
Output	Resistance 5.8Ω to 28Ω for temp sensor
Power requirement	5-14 V, ~18 mA for 1s
Power requirement	Minimum 5.5 V with 100 m cable
Environmental	IP68（-40 to +70°C）
Sample volume	~60 x 30 mm diameter
Sample volume	Sample volume is weighted towards soil immediately surrounding the rods
Dimensions and weight	Overall: 158 x 40 mm diameter Rods: 60 mm x 3.2 mm diameter (Rods are replaceable) Weight: 0.1 kg (exc. cable)
Sensor calibrations	Individual sensors are interchangeable Recalibration advised every 3 years (depending on use)
Soil calibrations	Generalised Mineral and Organic soil calibrations are supplied