SMT-100 Soil Moisture and Soil Temperature Probe
The SMT-100 soil moisture probes uses a Time Domain Transmission (TDT) technology. The SMT-100 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 SMT-100 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 SMT-100 utilises a ring oscillator to transform the signal’s travel time into a frequency.
The SMT-100 is available 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).
Then SMT-100 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.