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

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

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.

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)

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.