PlantCare has been able to develop a new type soil moisture sensor which eliminates the disadvantages of other sensor technologies. The PlantCare soil moisture sensor is based on a micro-thermal measurement and the result is - as with all other sensors - not an absolute value for the soil moisture, but a time, which is a measure of the soil moisture. A small tip is heated up by a heating element for a few seconds by about 1° C. After this heating period, the cooling curve is recorded electronically with great accuracy and the time required to reach a certain threshold is measured.
If the tip is immersed in water, the slightly heated tip cools rapidly as it cools slowly in the air. If this tip would be placed directly into the ground, the contact surface to the soil would not be defined, so that the readings would vary greatly. For this reason, the tip is surrounded by a felt. This hydrophilic felt encloses the tip completely and sucks the freely available water from the soil surrounding them. Therefore, the actual sensor does not feel the soil, but only the water-filled felt. Since the felt retains its properties for several years and also has a very low thermal conductivity compared to water, the sensor measures only the water present in felt.
The sensors measure the plant available water only.
The water contained in the roots is not measured. The measured values therefore do not change with the growth of plants and accordingly the increasing root volume.
The measuring range is from 0 to 100% which corresponds to 0-1500 hPa soil water potential.