L-WET LEAF WETNESS SENSOR

In agriculture, warm, wet weather promotes fungus diseases and moisture-loving insects. Direct surface wetness is pertinent because it is within the leaf micro-environment or on another plant surface that pathogens develop. Wetness data is usually reduced in practice to a yes or no form. For example, the Mills Tables are based on the hours that leaves remain wet while the temperatures are also warm. Danger arises as a period of warm wet weather is prolonged, and the danger passes only after a certain number of dry hours have elapsed. Wetness measurements are also useful when the exact time of the onset of rainfall is of interest, for example, as part of control systems that automatically open and close greenhouse windows or schedule irrigation. A rain guage is not useful for this purpose, because there is a delay before the rain guage accumulates enough water to signal its first count. Humidity sensors are not so useful either because there are many factors that determine precipitation. Sensitive wEtness measurements are also applicable to other areas of science and industry, such as the study of moisture in breath or of corrosion on metals.

The LWET from EME Systems is an artificial leaf surface constructed on a fiberglass circuit board. Moisture present on the surface increases the frequency output from an integrated oscillator circuit. The LWET is distinguished from similar products by having its AC excitation built in. It is not necessary to provide special excitation from the data logger. Changes in frequency of the LWET oscillator can be easily counted by our OWL2c data logger or other micro-controller. Alternatively, the LWET has voltage and current outputs directly proportional to the level of wetness the sensor can also be used with data loggers that have analog inputs. The LWET has identical sensing grids on top and bottom surfaces. The grids can be painted with exterior latex paint to make the response more akin to a natural leaf.

• Supply Voltage: 5--15 VDC
  less than 0.01% per Volt supply variation.
• Frequency output 50 hz dry @ infinite ohms
  10 khz wet @ zero ohms
  open collector square wave.
• Supply Current: 200±10µA dry to 1000µA wet
  Can be used as analog output signal
• Voltage output, 0.2 to 1 volt. 
• Operating Temperature: -0°C to +70°C
  no meaningful signal below 0°C
• connection to data logger, 10 foot cable
  4 wire flat telephone PVC jacket
  red: + 5 to 15 volts DC
  green: frequency signal, open collector, needs pull-up to +V, 50hz to 10khz
  white: voltage output signal, 0.2 volts to 1 volt.
  black: common, or analog current output.
• see SMX documentation for resistance response.
• lifetime: 1 to 3 years (depends on contaminants)
• Top & bottom sensor grids are 1.625' x 0.625'
  Overall size: 4.5' long x 0.75 wide x 0.031' thick, with mounting holes for #6 screw.
  Includes nylon loop for mounting.
  Pipe clamp not provided.