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SMT100 Soil Moisture and Soil Temperature Probe

The SMT100 soil moisture probe uses a Time Domain Transmission (TDT) technology. The SMT100 determines the volumetric water content and the soil temperature. It has a broad measurement range, it is maintenance free and frost resistant. With a robust design & manufacture and low power use, it is typically used for long-term observations (8+ years continuous use) and is well suited to IoT (Internet of Things) applications.

The SMT100 combines the advantages of the low-cost capacitance soil moisture sensor system with the accuracy of a TDR (time domain reflectometry) system. Like a TDR, it measures the travel time of a signal to determine the relative permittivity εr of the soil, and like a capacitance sensor, it converts εr into an easy to measure frequency. The SMT100 utilises a ring oscillator to transform the signal’s travel time into a frequency.

The SMT-100 is available in different variants in regards to the interface:

  • SMT100 SDI-12 (SDI-12 interface).
  • SMT100 analogue voltage output (0-10V or other voltage ranges on request).
  • SMT100 RS-485 (ASCII, MODBUS, TBUS).

SMT100 soil moisture probe measurements are much less affected by soil temperature, EC and texture in comparison to capacitance/FDR sensors. Sensor-to-sensor variability is moderate and accurate VSW% measurements are also possible with the SMT100 with out sensor-specific calibration.

Installed SMT-100 Soil Moisture Sensor