The SM150T is a capacitive soil moisture sensor developed and produced by Delta T Devices. Besides the soil moisture it also measures the soil temperature. Its sealed plastic body is attached to two sensing rods which insert directly into the soil for taking readings. A waterproof plug connects to a choice of signal cables. Both extension cables and extension tubes can be used. The sensor can be installed horizontal as well as vertical, at the surface as well as in deeper soil horizons.
The SM150T is powered by a data logger. The soil moisture output signal of the sensor is a differential analogue voltage signal (0 … 1.0 V DC ≈ 0 … 60 % Volume) and the soil temperature is provided as a resistant signal. The data logger stores the input signals and converts the soil moisture using the supplied general soil calibrations. It can also be calibrated for specific soils.
Besides all Delta-T Loggers the SM150T may be connected to any customary differential logger. The manual provides a detailed description how to configure. Additional it can be operated as a mobile sensor using the Moisture Meter HH150. Both devices are available as ThetaKit. (Note: the HH150 does not display or store SM150T temperature readings.)
The SM150T is a stable working measuring instrument with a low conductivity and temperature response. To quantify the effect on the results a clear overview is given in the manual how the output changes with different salt content or increasing temperature. As the salinity increases the effect on the measuring value decreases. Thus, the sensor operates in soils with high salt content as well (with special calibration up to 1000 mS/m).
The SM150T determines soil moisture by measuring the relative permittivity (εr) of the soil. Being a capacitive sensor the capacity of the integrated capacitor is calculated. When the relative permittivity changes the capacity changes too. Using regression formulas, e.g. Topp and Davis, εr can be converted into soil moisture. Typical application fields of soil moisture sensors are: irrigation control, hydrology, civil engineering, monitoring of contaminants, agriculture and forestry.
- soil specific calibration
- low energy consumption
- minimal soil disturbance
- low sensitivity to salinity
- operates in soils with special calibration up to 1000 mS/m
- adaptable cable system
Volumetric Water content
±3 % vol over 0 ... 70 % vol and 0 ... 60 °C
0 ... 100 % vol (50 - 100 % vol with reduced accuracy)
±5 % vol over 100 ... 1000 mS/m and 0 ... 60 % vol
|0 ... 1 V differentiell (≈ 0 ... 60 % vol)|
± 0,5 °C over 0 ... 40 °C (not including logger or cabling error)
-20 ... +60 °C
Soil moisture set SM150T (SM150T + HH150)