The SMX is an interface module for sensors that measure moisture content of soil or other substrates by way of their AC electrical resistance. The SMX provides three output modes, voltage, current or frequency, allowing the sensor to easily interface with a wide range of general purpose data logging equipment and meters.
The SMX prevents corrosion of the sensor by using AC excitation and by galvanically isolating it from unwanted underground DC currents.
The SMX is available in two forms. The SMX-oem is a circuit board, suitable for incorporation into custom systems in an enclosure. The SMX-encapsulated is potted in industrial epoxy with 6 wire leads, suitable for outdoor deployment.
The SMX is commonly used with the IRROMETER WATERMARK™ sensor. When buried at root depth, the WATERMARK reaches equilibrium with the local soil moisture and produces AC electrical resistance that is inversely proportional to soil moisture. (It also depends slightly on temperature.) The SMX converts this AC resistance to frequency, voltage, and current that can be read by data-loggers. More unusual applications have ranged from sensing moisture in airplane wing deicer bags to moisture in baby diapers.