SMT-100 Soil moisture probe

SMT-100 Soil moisture probe

Item no.: 1188311 (standard set) Item no.: 1188300 (analog 0-1 V) Item no.: 1188301 (analog 0-10 V) Item no.: 1188304 (analog 4-20 mA) Item no.: 1188303 (digital SDI-12) Item no.: 1188305 (digital RS 485, TrueLOG T-Bus) Item no.: 1188306 (digital RS 485, UGT-Bus) Item no.: 1188310 (digital RS 485, Modbus RTU) Item no.: 1188312 (digital RS 485, TBus ASCII)

Advantages at a glance

  • Reliable measurements
  • Fast response
  • Freeze-proof
  • Maintenance-free
  • Long service life

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SMT-100 Soil moisture probe

Compact, functional and robust: The SMT-100 combines the advantages of a cost-effective FDR sensor system with the accuracy of a TDR. As standard, we deliver the sensor in a practical carrying case set with a reader for mobile measurement of volumetric soil moisture and soil temperature. However, you can also order the SMT-100 separately either as an analog version with different voltage ranges or with a digital interface.

What can the SMT-100 do?

The sensor determines volumetric water content and temperature. It has a wide measuring range, is maintenance-free and frost-proof. With a fast response time and low sensitivity to salty soils, it is well suited for long observation periods. In addition to water content and temperature, the relative dielectric constant can also be output.

As with a TDR, the transit time of a signal is obtained to determine the relative dielectric constant εr of the soil. And, as with an FDR, εr is converted to an easily measured frequency. However, unlike other FDRs, this sensor is not based on capacitance measurement using a capacitor, but uses a ring oscillator to convert the signal propagation time into a frequency. The frequency used (>100MHz) is high enough to ensure a good function even in clayey soils.

How is the SMT-100 constructed?

The design is based on an integrated circuit board, which brings economic advantages. The blade shape simplifies installation in the ground. The housing and cable are sealed to be waterproof. Data processing and storage works via an external logger. The SMT-100 is bus compatible, so you can connect multiple devices to one logger.

Signal output - digital (RS485 with UGT-protocol. SDI-12 is available on request)
- analog (0-1V, other voltage ranges on request)

Cable length

Power supply

Power input


10 m

digital 4 ... 24 VDC (analog 12 ... 24 VDC)

40 mA during measurement

182 x 30 x 12 mm


Measurement range

0-60 % vol (0 ... 100 % vol with limited accuracy)

Accuracy with generic calibration

±3 % vol in mineral soils with average salinity over 0 ... 50 % vol

Accuracy after  specific calibration

±1 % vol


0.1 % vol



-40 ... +80 °C (analog -40 ... +60 °C)

extended temperature range on request


±0.2 °C (analog ±0.8 °C)


0.01 °C (analog 0.2 °C)

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