Decagon Leaf Wetness Sensor with the Sutron XLite 9210 Datalogger to measure and log hour of wetness.

1. Decagon Leaf Wetness Sensor with XLite 9210 Data
logger
Using the Decagon Dielectric Leaf Wetness Sensor with the XLite 9210 Data logger
Application Note
October 2013
Prepared by:
Integrated Systems Division
Copyright© 2008 Sutron Corporation

2. Decagon Leaf Wetness Sensor with Xlite9210 Datalogger 2
TABLE OF CONTENTS
PRODUCT OVERVIEW ............................................................................................................................................ 3
APPLICATION NOTE OVERVIEW .................................................................................................................................. 3
DECAGON LEAF WETNESS SENSOR ................................................................................................................. 3
XLITE 9210 DATALOGGER CONFIGURATION ................................................................................................. 5

3. Decagon Leaf Wetness Sensor with Xlite9210 Datalogger 3
PRODUCT OVERVIEW
APPLICATION NOTE OVERVIEW
The goal of this application note is to connect a Decagon Leaf Wetness Sensor with the Sutron XLite 9210 Datalogger to measure and log hour of wetness.
DECAGON LEAF WETNESS SENSOR
The LWS measures leaf surface wetness by measuring the dielectric constant of the sensor’s upper surface
Specifications
Measurement Time: 10 ms
Power: 2.5VDC @ 2mA, to 5VDC @ 7mA
Output: 320-1000 mV @ 3V excitation
Operating Environment: -20 to 60°C
Probe Dimensions: 11.2cm x 5.8cm x .075 cm
Cable Length: 5 m standard, extension cables are available
Connector Type: 3.5 mm plug or optional “pigtail” adapter (stripped and tinned lead wires)
Installation:
The LWS is designed to be deployed either in the canopy or on weather station masts. There are two holes in the non-sensing portion of the sensor body for mounting. The holes can be used with either zip ties or with 4-40 bolts.

4. Decagon Leaf Wetness Sensor with Xlite9210 Datalogger 4
Wiring the sensor to the XLite 9210 Data logger
When connect the sensor to the XLite 9210, the stereo plug can be clipped off, and the lead wires can be directly connected to the chosen logger. The wiring configuration is shown below.
White = 2.5 to 5V excitation
Bare shield = ground
Red = sensor output (single ended)

5. Decagon Leaf Wetness Sensor with Xlite9210 Datalogger 5
XLITE 9210 DATALOGGER CONFIGURATION
Most leaf wetness applications (disease forecasting, etc.) don't require knowledge of the amount of water on the surface - only if there is any water on the surface. To make this determination, a sensor output threshold corresponding to the minimum wet state must be identified.
The sensors are factory calibrated to read 445 raw counts when dry. But again the user will need to choose an acceptable threshold.
To start with, the user will need to use an ADC input block to measure the sensor in volts. As shown, in the properties of the ADC block, the user will need to select the Analog channel selected on the logger for the input and excitation channels. For the Measure Type, the user will need to select Voltage.
The conversion from the sensors raw count to mV with a 3000mv excitation is mV= raw counts * 0.733
It is important to remember that the XLite 9210 can only supply a 2.5 reference voltage, and the logger is measuring in volts and not mV. As such the conversion from the sensors raw count to V with a 2.5v excitation is V= raw counts * 0.00061
So to calculate raw count, we are taking the reading from the sensor in volts and dividing it by 0.00061.
We are then using the ACCUM processing block to calculate Hours of Wetness. As such, make sure to use the HRSSUN output of the ACCUM block.
In the example above, we are measuring hours of wetness on a daily basis at midnight while taking one minute samples. Thu we will only get one value logged at midnight, and f the raw count is above 450, this would be considered a minute of wetness. At the end of the day, the logger will accumulate all one minute samples above 450 and give us total hours of wetness for that day.