Truebner SMT50 analog soil moisture sensor

The soil moisture sensor SMT50 is a maintenance-free capacitive probe. Capacitive probes have
several advantages against other soil moisture sensors. They respond immediately to changes in the
volumetric soil moisture content and there are no bare metal electrodes in contact with the soil.
There is no corrosion of the sensor. The SMT50 is very robust, durable and maintenance-free.
Capacitive soil moisture sensors generate an alternating electric field around its measurement
electrodes. The electric field penetrates the surrounding soil. The electric circuit inside the sensor
measures the resulting total capacitance of the electrodes, which depends on the volumetric water
content of the soil. The higher the volumetric water content, the higher is the resulting capacitance.
The measured value is computed by an integrated microcontroller and converted to a linear voltage
output signal (0…3V, yellow wire).
The temperature is measured by an additional temperature sensor which is located inside the black
housing of the sensor. The linear temperature signal is output on the green wire. For a correct soil
temperature measurement it is important to fully burry the probe in the soil.

Specifications

• Soil volumetric water content (VWC): Using factory calibration up to ± 3% (VWC) in mineral soils with moderate salinity from 0 to 50% VWC
• Temperature:Typical ± 0.8°C
• Resolution: 8 bit = 0.2% volumetric water content 10 mV/°C
• Range: 0 to 50% volumetric water content, Temperature: -20 to +85°C
• Output signals: 0 – 3 V linear for volumetric water content
• Startup time: 300 ms
• Output resistance: 10 kOhm
• Power: 3.3-30 V DC, 2.7 mA
• Cable length: 10 m
• Sensor dimensions: ca. 13.5 cm x 2.15 cm
• Data logger compatibility: Logger capable of appropriate power excitation and suitable analog inputs

OpenSprinkler

You need the analog sensor board to connect up to 8 soil moisture sensors (up to 16 soil moisture sensors with 2x analog sensor boards)

Also a firmware update is needed, please install OpenSprinklerShop firmware

References

technical data and installation_Guide_SMT50

Truebner homepage