SMT100 Soil moisture and soil temperature

The SMT100 soil sensor allows for easy, inexpensive soil moisture and temperature measurements. This device enables both the precise analysis of the soil water balance and the determination of plant soil water availability. The SMT100’s integrated temperature sensor additionally provides important data on ground temperature. The device’s numerous applications range from data collection for scientific purposes to irrigation control in commercial agriculture and horticulture.

Through its special design and optimized measuring principle, the SMT100 combines the advantages of low-cost FDR sensors with the accuracy of TDR measurements. Where other soil moisture sensors reach their limits, the high operation frequency (> 100 MHz) as used in SMT 100 measurements allows allow this sensor to take reliable measurements even in dense clay soils. Further advantages include the short measuring time, a low sensitivity to salinity, and a large measuring range. Sensor and cable are maintenance-free, waterproof and frost-resistant. The SMT100 is therefore ideal for continuous operation.

The compact, functional and robust design of the glass-fiber reinforced, blade-shaped sensors enable simple installation for permanent measurements or easy insertion into the soil for manual point measurements with handset. Variants with different communication protocols (RS-485, SDI-12) as well as a version with analogue output are also available.


  • Accurate determination of soil water content
  • Integrated temperature measurement
  • Suitable for every soil type
  • Easy installation (ongoing measurement) and insertion (manual measurement with handset) into soil
  • Cost-effective
  • Compatible with almost every logger system (interface options: Analogue Volt Signal, RS-485, SDI-12)

Technical Data

Sensor model name

Soil moisture and soil temperature sensor

Type SMT100

Scope of application

For continuous (permanent installation) or manual (insertion with handset) measurements of the volumetric water content of soil (SWC).

Suitable for

All soil types

Special features/limitations

Special feature: read out of additional information possible: »Raw data, dielectric permittivity

Limitation: Use for manual point measurements in highly abrasive technosols is not recommended

Measurement range


0 to 60% volumetric water content (up to 100% volumetric water content with restricted accuracy)


Temperature: -40 to + 80 ° C (analogue version -40 to + 60 ° C)


0.1% SWC

0.01 ° C (analogue version 0.2 ° C)


Volumetric water content (SWC)

  • at factory calibration up to ± 3% (SWC) in mineral soil types with medium salinity of 0 to 50% VW
  • for soil-specific calibration up to ± 1% (SWC)


  • typical ± 0.2 ° C, max. ± 0.4 °C over the entire measuring range (analogue version ± 0.8 °C)

Logger requirements and sensor output signal

All data loggers with suitable power supply and RS485

Interface (TBus, Modbus, ASCII), SDI-12 or

Analogue input 0 – 10 V (other voltage ranges on request)

Power supply

4 – 24 V DC, up to 40 mA peak during measurement

(Analogue version 12 – 24 V DC for 0 – 10 V output signal)

Measuring time digital versions: less than 50 ms

Measuring time analogue versions: less than 500 ms

Operational conditions

Air temperature: -25 to 70 ° C, rel. air humidity: 0 to 100%

Size & Weight (sensor without cable)

18.2 cm x 3 cm x 1.2 cm; about 80 g without cable

Sensor cable length

10 m, can be extended on request


Technical data sheets

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Accessories & Compatible Products

Compatible sensors and peripherals:

From small and compact to an extensive measuring network, Ecomatik offers complete system solutions for sensor data acquisition in any desired size:


SMT soil moisture and soil temperature sensors are available in different output signal configurations. Availiable output options are analog DC, SDI-12 and RS485. They are therefore compatible with almost all common data loggers and microcontrollers with analog voltage input channels or digital SDI-12 or RS485 inputs. If you are unsure about the compatibility of an existing data logger, you are welcome to contact us at any time.


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General information on order processing

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Assessment of your needs

With your consideration and input, we determine which of our products best meet your needs. We are also happy to design fully-integrated measuring stations (plant, climate, soil sensors), including an independent power supply and mobile data transmission, depending on your requirements.

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Perfect, then just write us an email! In your order, please state the diameter of your measuring objects in addition to the required cable lengths.

Your contact details and Assessment of your needs

Like so many things, everything started with an idea ...

In the case of the plant scientist and founder of ECOMATIK, Dr. Liu, it was the idea that modern measurement technology should enable crucial plant physiological parameters to be measured directly, precisely and with high temporal resolution on the plant itself. It was obvious to him that there is an information potential of immense value in the detailed understanding of immediate reactions of plants to their environment...