Polarmoist, an alternative way to measure surface moisture
Because it uses uses near-infrared light, Polarmoist can measure the surface moisture of sand, aggregates and other granular materials as they pass by on a belt or flow out of a hopper, without making contact. In comparison, AquaSense and AquaMix must be in contact with the material and they measure bulk moisture (but can be calibrated to read surface moisture percentage). It is the only system that can measure the surface moisture of large aggregates (greater than 3/8″ or 10 mm); capacitance and microwave methods show too much variation. The sensor uses an LED light source and solid-state detection with a narrow-beam lens to focus on the stream of material. A low volume air supply keeps the lens clear of dust. This is necessary in most applications such as sand, because a lot of dust is raised as it is handled.
Conveyor belt: The sensor is positioned so that its field of view includes the sand on the belt but never any part of the belt itself. The sensor averages the signal as the material travels past the viewing zone.
Clam gate: The sensor is positioned to view the falling material between the gate and the hopper or belt. the averaging starts when the gate opens and continues while the material is falling.
Mixer: The sensor views the surface of the mixing material. If water is added, time must be allowed for the water to be thoroughly mixed into the material, to minimize the error in the surface moisture measurement..