The SMT100 Soil Moisture and Soil Temperature Probe determines the volumetric water content and the soil temperature for long-term observations using Time Domain Transmission (TDT). 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.
Specifications:
Soil volumetric water content (VWC):
- Using factory calibration up to ± 3% (VWC) in mineral soils with moderate salinity from 0 to 50% VWC
- Using medium specific calibration up to ± 1% (VWC)
Temperature: Typical ± 0.2°C, max. ± 0.4°C over full range (analog version ± 0.8°C)
Resolution: 0.1% volumetric water content or better 0.01°C or better (analog version 0.2°C)
Measurement Range:
- 0 to 60% volumetric water content (up to 100% volumetric water content with limited accuracy)
- Temperature: -40 to +80°C (analog version -40 to +60°C)
Digital output options:
- RS-485 with TBUS
- RS-485 with Modbus
- RS-485 with ASCII SDI-12
Analogue Outputs:
- 0 – 10 V (other voltage ranges on request)
- 4-20 mA (only volumetric water content)
Power: 4-24 V DC, up to 40 mA during measurement (analogue version 12 – 24 V DC for 0 – 10 V output)
Measurement time:
- digital versions: less than 50 ms
- analogue versions: less than 500 ms
Cable length: 10m
Sensor dimensions: 18.2 cm x 3 cm x 1.2 cm
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