Decagon Devices Dielectric Leaf Wetness Sensor Owner's/operator's Manual

Operator’s Manual

Decagon Devices, Inc.

Version: February 29, 2016 — 11:10:55

LWS

Decagon Devices, Inc.

2365 NE Hopkins Court

Pullman WA 99163

Phone: [phone]

Fax: [phone]

Website: www.decagon.com

Email: [e-mail] or [e-mail]

Trademarks:

“ECH2O” is a registered trademark of Decagon Devices, Inc.

All Rights Reserved

c

2007-2014 Decagon Devices, Inc.

All Rights Reserved

ii

LWS CONTENTS

Contents

1 Introduction 1

1.1 Customer Support . . . . . . . . . . . . . . . . . . . . 1

1.2 About This Manual . . . . . . . . . . . . . . . . . . . 1

1.3 Warranty . . . . . . . . . . . . . . . . . . . . . . . . . 2

1.4 Seller’s Liability . . . . . . . . . . . . . . . . . . . . . . 2

2 About the Leaf Wetness Sensor 3

2.1 Specifications . . . . . . . . . . . . . . . . . . . . . . . 3

3 Collecting Data 5

3.1 Installing the Sensor . . . . . . . . . . . . . . . . . . . 5

3.2 Data Logger Requirements . . . . . . . . . . . . . . . . 6

3.3 Adapter Cable Wiring . . . . . . . . . . . . . . . . . . 6

3.4 Extending the Sensor Leads . . . . . . . . . . . . . . . 7

3.5 UV Protection . . . . . . . . . . . . . . . . . . . . . . 7

4 Interpreting Data 8

4.1 Understanding Data from the Em50 . . . . . . . . . . 9

4.1.1 Processed Data File . . . . . . . . . . . . . . . 9

4.1.2 Unprocessed Data File . . . . . . . . . . . . . . 10

4.1.3 DataTrac3 File . . . . . . . . . . . . . . . . . . 11

4.2 Understanding Data from Other Data Loggers . . . . 11

5 LWS Theory 12

5.1 How the LWS Works . . . . . . . . . . . . . . . . . . . 12

5.2 How the LWS Mimics a Real Leaf . . . . . . . . . . . 12

6 Appendix A: Sample CSI Program 14

7 Declaration of Conformity 16

iii

LWS 1 INTRODUCTION

1 Introduction

Thank you for choosing Decagon’s Dielectric Leaf Wetness Sensor.
We designed this sensor to accurately and affordable measure the
duration of leaf-surface wetness. This manual should help you un­derstand the sensor features and how to use it successfully.

1.1 Customer Support

There are several ways to contact Decagon if you ever need assis­tance with your product, have any questions, or feedback. Decagon
has Customer Service Representatives available to speak with you
Monday through Friday, between 7 am and 5 pm Pacific time.

Note: If you purchased your sensor through a distributor, please con­tact them for assistance.

Email:
[e-mail] or [e-mail]

Phone:
509-332-5600

Fax:
509-332-5158

If contacting us by email or fax, please include as part of your mes­sage your instrument serial number, your name, address, phone, fax
number, and a description of your problem or question.

1.2 About This Manual

Please read these instructions before operating your sensor to ensure
that it performs to its full potential.

1

1 INTRODUCTION LWS

1.3 Warranty

The Dielectric Leaf Wetness Sensor has a 30-day satisfaction guar­antee and a one-year warranty on parts and labor. Your warranty is
automatically validated upon receipt of the instrument.

Note: The one year service plan activates when Decagon ships the
instrument and not at the time of software installation.

1.4 Seller’s Liability

Seller warrants new equipment of its own manufacture against de­fective workmanship and materials for a period of one year from the
date of receipt of equipment.

Note: We do not consider the results of ordinary wear and tear,
neglect, misuse, or accident as defects.

The Seller’s liability for defective parts shall in no event exceed the
furnishing of replacement parts “freight on board” the factory where
originally manufactured. Material and equipment covered hereby
which is not manufactured by Seller shall be covered only by the
warranty of its manufacturer. Seller shall not be liable to Buyer for
loss, damage or injuries to persons (including death), or to property
or things of whatsoever kind (including, but not without limitation,
loss of anticipated profits), occasioned by or arising out of the instal­lation, operation, use, misuse, nonuse, repair, or replacement of said
material and equipment, or out of the use of any method or process
for which the same may be employed. The use of this equipment con­stitutes Buyer’s acceptance of the terms set forth in this warranty.
There are no understandings, representations, or warranties of any
kind, express, implied, statutory or otherwise (including, but with­out limitation, the implied warranties of merchantability and fitness
for a particular purpose), not expressly set forth herein.

2

LWS 2 ABOUT THE LEAF WETNESS SENSOR

2 About the Leaf Wetness Sensor

The LWS measures leaf surface wetness by measuring the dielectric
constant of the sensor’s upper surface (see Section 5 for a more thor­ough explanation). It has a very low power requirement, which gives
you the ability to make as many measurements as you want over a
long period of time (such as a growing season) with minimal bat­tery usage. This sensor also has very high resolution, which gives
you the ability to detect very small amounts of water (or ice) on the
sensor surface. Water on the sensor surface does not need to bridge
electrical traces to be detected, as is common with resistance based
surface wetness sensors. This means that the LWS does not need
to be painted before use, which eliminates the need for individual
sensor calibration.

2.1 Specifications

Measurement Time: 10 ms

Power: 2.5 VDC @ 2 mA to 5 VDC @ 7 mA

Output: 320 to 1000 mV @ 3 V excitation

Operating Environment: -20 to 60◦C

Probe Dimensions: 11.2 cm x 5.8 cm 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)

Data Logger Compatibility (not exclusive):

Decagon: Em50, Em50R
Campbell Scientific: CR10, 10X, 21X, 23X, 1000, 3000, 5000

3

2 ABOUT THE LEAF WETNESS SENSOR LWS

Figure 1: The Leaf Wetness Sensor

4

LWS 3 COLLECTING DATA

3 Collecting Data

3.1 Installing the Sensor

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.

Figure 2: Top View of Installed LWS in Plant Canopy

5

3 COLLECTING DATA LWS

3.2 Data Logger Requirements

The LWS works with Decagon’s 5-channel Em50 or Em50R data log­gers. It can also be adapted for use with other data loggers, such as
those from Campbell Scientific, Inc. (See Appendix A for a sample
program.) The sensor requires an excitation voltage in the range of

2.5 to 5 volts.

It produces an output voltage that depends on the dielectric con­stant of the medium surrounding the probe, and ranges between 10
to 50% of the excitation voltage. Any data logger which can produce
a 2.5 to 5 V excitation with approximately 10 millisecond duration
and read a volt level signal with 12-bit or better resolution should
be compatible with the LWS. The current requirement at 2.5 V is
around 2 mA, and a 5 V it is 7 to 8 mA.

Note: The LWS is intended only for use with data loggers and readout
devices which can provide short excitation pulses, leaving the probes
turned off most of the time. Continuous excitation not only wastes
battery power, but may, under certain circumstances, cause the probe
to exceed government specified limits on electromagnetic emissions.

3.3 Adapter Cable Wiring

If you use a non-Decagon data logger, clip the stereo plug off and
connect the lead wires directly to the chosen logger. The wiring con­figuration is shown below.

White = Power 2.5 to 5 V excitation
Bare shield = Ground
Red = Sensor data output (single ended)

6

LWS 3 COLLECTING DATA

Figure 3: Sensor wiring diagram

3.4 Extending the Sensor Leads

Extension cables for the LWS are available from Decagon in 10 and
50 foot (3 and 15 meter) lengths. The leads can be extended up to
250 feet without signal attenuation.

When using these extension cables in an unprotected environment,
the junctions between cables must be waterproofed. This can be ef­fectively accomplished by connecting the junction, applying silicone
sealant to the junction, and shrinking appropriately sized heat-shrink
tubing over the still wet silicone sealant.

3.5 UV Protection

The LWS leaf wetness sensor is designed to withstand typical out­door radiation and precipitation loads for greater than two years. If
you are using the LWS in areas with non-typical (unusually high) ra­diation loads, we recommend additional applications of McNett UV
Tech (available from http://www.mcnett.com) be reapplied every 45
days. McNett is the only tested and approved UV blocking system
for Decagon’s Leaf Wetness Sensor.

To apply McNett UV Tech:

1. Wipe sensor clean.

2. Spray sensor surface with McNett UV Tech.

3. Rub with soft cloth until dry.

7

4 INTERPRETING DATA LWS

4 Interpreting Data

Most leaf wetness applications (disease forecasting, etc.) do not 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.

When read with the EM50 data logger, the LWS outputs 445 raw
counts when dry. When the sensor is totally wet, as in a heavy rain,
the signal can range up to around 1400 counts. Varying amounts of
water on the surface of the sensor cause a sensor output proportional
to the amount of water on the sensor’s surface.

Figure 4: Sample raw output from the LWS

Because ice has a much lower dielectric constant than that of liquid
water, the sensor output from frost is much lower than that from a
similar amount of rain or dew.

Note: Over time, the accumulation of dust and bird dropping can

8

LWS 4 INTERPRETING DATA

cause the dry output to rise. We recommend that the sensor be
cleaned using a moist cloth periodically, or when you detect elevated
dry output.

4.1 Understanding Data from the Em50

With Decagon’s Em50 and Em50R data loggers, users have multi­ple options for interpreting data. The sensors are factory calibrated
to read 445 raw counts when dry. When you configure an Em50 or
Em50R port to read a leaf wetness sensor, the logger reads the sen­sor every minute and compares the data to two pre-defined wetness
thresholds of 450 and 460 raw counts. When you collect the data
from the logger with ECH2O Utility there are several options for the
format of the data output.

4.1.1 Processed Data File

Processed Excel File

When a precessed data file format is selected, three columns of data
are output for each LWS port.

Column 1: The number of minutes that the LWS output was over
450 raw counts in the preceding wake interval. So, if you shoose a 30
minute wake interval then the number can range from 0 (the sensor
was never wet during the 30 minute period) to 30 (the sensor was
always wet during that 30 minute period). Take the sum of these
numbers in this column to yield the cumulative wetness duration ­minutes - during the time period of interest.

Column 2: The number of minutes that the LWS output was over
460 raw counts in the preceding wake interval. The data in this
column follow the same format as those in column 1, only with the
wetness threshold set slightly higher. Field tests for the LWS indi­cate the extreme dust buildup or bird droppings can cause the dry
output of the sensor to climb above the 450 raw count threshold. If
this occurs, the data in column 2 can be used until the sensor can be

9

4 INTERPRETING DATA LWS

cleaned.

Column 3: The final reading (in raw counts) of the LWS during
the wake interval. So, if again a 30 minute wake interval has been
chosen, the number in column 3 is the output in raw counts from
the LWS during the last minute of that 30 minute period. This data
column is output in case an extreme contamination event occurs,
forcing the dry output higher than 460 raw counts. In this case,
the user can identify an new wetness threshold from the time series
data, and calculate wetness duration from the new threshold until
the sensor can be cleaned. See the section at the end of this chapter
titled “Understanding Data from Other Data loggers” for more infor­mation on this procedure. When using the data in this column, the
user can only obtain a wetness reading every wake interval (typically
30 minutes or more), instead of the one minute wetness resolution
available in column 1 and 2. Note that the conversion from Em50
raw counts to mV with 3,000 mV excitation is mV = raw counts ×

0.733.

4.1.2 Unprocessed Data File

When an unprocessed Excel file format is downloaded, three columns
of data are output for each LWS port.

Column 1: The cumulative number of minutes that the LWS out­put has been over 450 raw counts since the Em50 data were last
erased or the accumulator has rolled over.

Note: The accumulator has a maximum of 2,048 minutes (1.42 days)
of wetness. If the cumulative wetness duration exceed this window
(which likely happens often), then the accumulator resets to zero and
begins accumulating again.

Column 2: The cumulative number of minutes that the LWS out­put has been over 460 raw counts since you last erased the Em50 or
rolled over the accumulator. Again, this accumulator rolls over to
zero after 2,048 minutes of wetness.

10

LWS 4 INTERPRETING DATA

Column 3: The final reading (in raw counts) of the LWS during

the wake interval. (See column 3 description under precessed the
files above)

4.1.3 DataTrac3 File

When you download the DataTrac3 file format (.dxd), a single 10
digit number downloads for each sensor. The .dxd format easily
imports into Decagon’s convenient DataTrac3 graphing software. It
also has the advantage that it can be converted with EC H2O Utility
to the other file formats listed above. See the manual for your Em50
data logger for details on exporting data.fform

4.2 Understanding Data from Other Data Loggers

With non-Em50 data loggers, the user needs to establish a wetness
threshold for their system. The dry output of the LWS varies with
excitation voltage (note that the acceptable excitation voltage range
is 2.5 to 5 V). The LWS dry output is easily determined from time
series data such as those presented in Figure 4. A wetness threshold
should be chosen that is slightly above the dry output, and subse­quent readings should be compared to the dry output to determine
surface wetness. When using a non-Em50 data Logger, it is im­portant to collect data frequently enough to capture changes in the
surface wetness. A sampling frequency of 15 minutes or less is often
necessary to accurately capture leaf wetness duration.

11

5 LWS THEORY LWS

5 LWS Theory

5.1 How the LWS Works

The LWS measures the dielectric constant of a zone approximately
1 cm from the upper surface of the sensor. The dielectric constant
of water (80) and ice (5) are much higher than that of air (1), so the
measured dielectric constant strongly dependends on the presence of
moisture or frost on the sensor surfaces. The sensor outputs a mV
signal proportional to the dielectric of the measurement zone, and
therefore proportional to the amount of water or ice on the senor
surface.

5.2 How the LWS Mimics a Real Leaf

The sensor has been specially designed to closely approximate the
thermodynamic properties of a leaf. If the specific heat of a leaf is
estimated at 3,750 j kg−1K−1, the density is estimated to be 0.95
g/cm3, and the thickness of a typical leaf is 0.4 mm, then the heat
capacity of the leaf is 1,425 J m−2K−1. This is closely approximated
by the thin (0.65 mm) fiberglass construction of the LWS, which has
a heat capacity of 1,480 J m−2K−1. By mimicking the thermody­namic properties of a real leaf, the LWS more closely matches the
wetness state of the canopy.

The sensor has also been engineered to closely match the radiative
properties of real leaves. Healthy leaves generally absorb solar radi­ation effectively in much of the visible portion of the spectrum, but
selectively reject much of the energy in the near-infrared portion of
the spectrum. The surface coating of the LWS absorbs well in the
near-infrared region, but the white color reflects most of the visible
radiation. Spectrophotometer measurements indicate that the over­all radiation balance of the sensor closely matches that of a healthy
leaf. During normal use, prolonged exposure to sunlight can cause
some yellowing of the LWS. This is expected and does not affect the
probes function.

The surface coating of the LWS is hydrophobic – similar to a leaf

12

LWS 5 LWS THEORY

with a hydrophobic cuticle. The sensor should match the wetness
state of these types of leaves well, but may not match the wetness
duration of leaves with plentiful leaf hairs or less waxy cuticles. It
is impossible for any sensor to accurately mimic the properties of all
leaves.

The LWS is engineered to be repeatable among units, so that re­lationships can be determined between the wetness state of the sen­sor, and the wetness state of various agricultural or natural plant
canopies. Painting and individual sensor calibration is not necessary
with the LWS.

13

6 APPENDIX A: SAMPLE CSI PROGRAM LWS

6 Appendix A: Sample CSI Program

;{CR23X}
;
;Program to read Decagon’s Dielectric Leaf Wetness ;Sensor (LWS)
;
;Wiring: white to EX1, red to 1H, shield to gnd
;
;This program separates LWS output into three bins
;bin 1 = output < 330mV - dry sensor
;bin 2 = 330mV < output < 337mV - wet sensor even when contaminated
;bin 3 = output > 337 mV - wet sensor even when contaminated
;The values output to final storage by the histogram
;command are the fraction of the OUTPUT INTERVAL that
;had sensor output in the preceding ranges
;
;Note that the wetness thresholds depend on excitation
applied. If you are exciting with other than ;3000 mV,
you will need to determine a custom wetness ;threshold

*Table 1 Program
01: 1 Execution Interval (seconds)

1: Excite-Delay (SE) (P4)

1: 1 Reps
2: 20 Auto, 60 Hz Reject, Slow Range (OS>1.06)
3: 1 SE Channel
4: 1 Excite all reps w/Exchan 1
5: 1 Delay (0.01 sec units)
6: 3000 mV Excitation
7: 1 Loc [ LWS_mV ]
8: 1.0 Multiplier
9: 0.0 Offset

2: If time is (P92)

1: 0 Minutes (Seconds --) into a
2: 60 Intervl (same units as above)
3: 10 Set Output Flag High (Flag 0)

3: Real Time (P77)^14490’

1: 1110 Year,Day,Hour/Minute (midnight = 0000)

4: Sample (P70)^21634

1: 1 Reps
2: 1 Loc [ LWS_mVn ]

14

LWS 6 APPENDIX A: SAMPLE CSI PROGRAM

5: Histogram (P75)^15793

1: 1 Reps
2: 3 No. of Bins
3: 0 Open Form
4: 1 Bin Select Value Loc [ LWS_mV ]
5: 0 Frequency Distribution
6: 330 Low Limit
7: 337 High Limit

*Table 2 Programs

02: 0.0000 Execution Interval (seconds)

*Table 3 Subroutines

End Program

15

7 DECLARATION OF CONFORMITY LWS

7 Declaration of Conformity

Application of Council Directive: 2004/108/EC and 2011/65/EU

Standards to Which EN61326-1:2013
Conformity is Declared: EN62321:1998

Manufacturer’s Name: Decagon Devices, Inc

2365 NE Hopkins Ct.
Pullman, WA 99163 USA

Model Number: LWS-1

Year of First Manufacture: 2006

This is to certify that the Dielectric Leaf Wetness Sensor, manufactured by
Decagon Devices, Inc., a corporation based in Pullman, Washington, USA meets
or exceeds the standards for CE compliance as per the Council Directives noted
above. All instruments are built at the factory at Decagon and pertinent testing
documentation is freely available for verification.

16

Index

Contact Information, 1
Customer Support, 1

Data, 5

Interpretation, 8

Data Logger, 3

Data from Non-Decagon loggers,

10
Extending Sensor Leads, 7
Requirements, 6
Sample CSI program, 14
Wiring Configuration, 6

DataTrac3, 11

Files, 11

Dielectric Measurement, 12

ECH2O Utility, 9

Processed Data File or tab delim-

ited text file, 9
Unprocessed Data File, 10

Email, 1

Fax, 1

Installation, 5

LWS

Operation, 5
Thermal Properties, 12

Seller’s Liability, 2
Specifications, 3

Theory of Operation, 12

UV Protection, 7

Warranty, 2

17