Schelt Technology

OPERATING PRINCIPLE: The WATERMARK sensor is a resistive device thatresponds to changes in soil moisture. Once planted in the soil, it exchangeswater with the surrounding soil thus staying in equilibrium with it.Soil water is an electrical conductor thereby providing a relative indication ofthe soil moisture status. As the soil dries, water is removed from the sensorand the resistance measurement increases. Conversely, when the soil isrewetted, the resistance lowers.The WATERMARK sensor is unique in that it takes its resistive measurementwithin a defined and consistent internal matrix material, rather than using thesurrounding soil as the measurement medium. This unique feature allows thesensor to have a stable and consistent calibration that does not need to beestablished for every installation.The relationship of ohm of resistance to centibars (cb) or kilopascals (kPa) ofsoil water tension is constant and built into the reading devices that are usedto interrogate the sensor. The sensor is calibrated to report soil water tension,or matric potential, which is the best reference of how readily available soil