Truebner SMT100 digital soil moisture sensor RS485

The SMT100 is a maintenance free capacitive sensor based on the TDT (time domain transmission)
principle. This method uses the propagation of electrical signals along the green sensor blade. Higher
soil moisture increases the dielectric permittivity of the soil and slows down signal propagation. The
measurement value is processed by an internal microcontroller, so that the SMT100 will provide raw
data (“counts”), dielectric permittivity of the soil and volumetric water content using the so-called Topp-equation.

Generally, TDT sensors are using a high measurement frequency (> 150 MHz) which makes them
much less affected by the electrical conductivity of the soil. Therefore, TDT sensors can also be used
for applications where higher conductivity can be expected (e.g. fertilizer enriched soils).
The integrated temperature sensor is located in the black housing. In order to measure soil
temperature the sensor has to be completely embedded in the soil.

This version is for RS485 modbus. With the truebner software, you can also switch to RS485 ascii

Specifications

• digital RS485 Modbus interface
• provides soil moisture, temperature and permittivity values of the soil
• 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)
• Additional output (digital versions only):Raw measurement data
  Dielectric permittivity
• Resolution:0.1% volumetric water content or better
  0.01°C or better (analog version 0.2°C)
• Range0 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)
• Output options:RS-485 with Modbus
  RS-485 with ASCII
•  Power:4-24 V DC, up to 40 mA during measurement (analog version 12 – 24 V DC for 0 – 10 V output)
  Measurement time digital versions: less than 50 ms
  Measurement time analog versions: less than 500 ms
• Cable length:10m
• Sensor dimensions:18.2 cm x 3 cm x 1.2 cm
• Data logger compatibility:Logger capable of appropriate power excitation and RS-485 (TBUS, Modbus, ASCII), SDI-12 or analog input
  Free PC logger software available on request

OpenSprinkler

You can connect up to 64 sensors to one Truebner Modbus adapter.

Also a firmware update is needed, please install OpenSprinklerShop firmware

References

Manual_SMT100_V1.0 SMT100_Flyer_EN

SMT100_Flyer_EN

Truebner homepage