OWL2c and conductivity

Posted on Feb 6, 2014

Moisture deposited on a surface bridges across a grid of wires or circuit board traces. A circuit measures the AC ohms resistance through the grid. - Warm wet weather promotes fungus and insect pests of plants. - Quick detection of rain can be used in controllers for greenhouse windows and the like. - Grids can be used to detect the moisture in breath, condensation

OWL2c and conductivity
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from steam, or spray from industrial or other processes. Stainless steel electrodes are embedded in a block of plaster of paris (gypsum) or in a proprietary mixture. Watermark ™ sensors are "granular matrix" devices, that have a fine sand aggregate along with gypsum crystals, held inside a permeable membrane and stainless steel sleeve. The purpose of the gypsum is to buffer the conductance measurement from ions that are found in uncontrolled amounts in the soil. This device is buried in close contact with soil, and reaches an equilibrium with the soil moisture. The AC ohms resistance of the block can be correlated with soil moisture or with evidence of plant stress. We have an assembled " SMX " module available for reading the resistance of Watermark blocks into the OWL2 or BASIC Stamp. Electrodes touch the surface of the water, to indicate attainment of a certain water level. This can initiate an action or alarm, or operate a sump pump. An output can be taken as the water moves up and down a pair of electrodes, and the level is correlated with resistance values on the scale. The signal depends on both the water level and on the specific conductivity of the water. See Earth Measurements, units 5 and 6. By making the water fill an exact geomerical space, the variable becomes the conductivity of the water. The circuit measures the resistance of the water at a certain temperature, which is measured at the same time....

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