Decagon GS3 Bedienungsanleitung
Operator’s Manual
Decagon Devices, Inc.
Version: December 1, 2014 — 11:53:59
GS3
Decagon Devices, Inc.
2365 NE Hopkins Court
Pullman WA 99163
Phone: 509-332-5600
Fax: 509-332-5158
Website: www.decagon.com
Trademarks
c
2011-2014 Decagon Devices, Inc.
All Rights Reserved
ii
GS3 CONTENTS
Contents
1 Introduction 1
1.1 Customer Support . . . . . . . . . . . . . . . . . . . . 1
1.2 Specifications ....................... 2
1.3 Warranty ......................... 3
2 Theory 5
2.1 Volumetric Water Content . . . . . . . . . . . . . . . . 5
2.2 Temperature ....................... 5
2.3 Electrical Conductivity . . . . . . . . . . . . . . . . . . 5
2.4 Converting Bulk EC to Pore EC . . . . . . . . . . . . 6
2.5 Pore Water vs. Solution EC . . . . . . . . . . . . . . . 7
2.6 Reference ......................... 8
3 Calibration 9
4 Connecting Sensors 10
4.1 Connecting to an Em50/Em50R logger . . . . . . . . . 10
4.2 3.5mm Stereo Plug Wiring . . . . . . . . . . . . . . . . 10
4.3 Connecting to a Non-Decagon Logger . . . . . . . . . 11
5 Communication 13
5.1 Serial Communication . . . . . . . . . . . . . . . . . . 13
5.2 SDI-12 Communication . . . . . . . . . . . . . . . . . 13
5.3 SensorBus ........................ 15
5.4 Address .......................... 15
5.5 Power ........................... 16
5.6 Reading .......................... 16
5.7 Campbell Scientific Programs . . . . . . . . . . . . . . 17
6 Installing the Sensors 18
6.1 Orientation ........................ 18
6.2 Removing the Sensors . . . . . . . . . . . . . . . . . . 19
6.3 Cleaning the Probes . . . . . . . . . . . . . . . . . . . 19
7 Troubleshooting 21
8 Declaration of Conformity 23
iii
GS3 1 INTRODUCTION
1 Introduction
Thank you for choosing Decagons GS3 Greenhouse Sensor. We de-
signed the GS3 to measure the water content, electrical conductivity
and temperature of many types of growing media. Decagon devel-
oped the GS3 primarily to work in greenhouse applications where
the slim, stainless steel needles could be inserted easily into many
types of substrates, but it can work in many other applications as
well. This manual guides you through the sensor features and how
to use it successfully.
1.1 Customer Support
If you ever need assistance with your GS3, or if you just have ques-
tions or feedback, there are several ways to contact us. Customer ser-
vice representatives are available to speak with you Monday through
Friday, between 7am and 5pm Pacific time.
Note: If you purchased your GS3 through a distributor, please con-
tact them for assistance.
Email:
Phone:
509-332-5600
Fax:
509-332-5158
If contacting us by email or fax, please include as part of your mes-
sage your instrument serial number, your name, address, phone, and
fax number.
1
1 INTRODUCTION GS3
1.2 Specifications
Volumetric Water Content
Accuracy: εa:±1εa(unitless) from 1 to 40 (soil range), ±15% from
40 to 80:
•Using a generic calibration: ±0.03 m3
m3(±3% VWC) typical
in mineral soils that have solution electrical conductivity <5
dS/m
•Using medium specific calibration, ±0.01 to 0.02 m3
m3(±1 to
2% VWC) in any porous medium
Resolution:
•εa: 0.1 εa(unitless) from 1 to 20
•<0.75 εa(unitless) from 20 to 80
•0.002 m3
m3(0.2% VWC) from 0 to 40% VWC
•0.001 m3
m3(0.1% VWC) >40% VWC
Range: Apparent dielectric permittivity (εa): 1 (air) to 80 (water)
Bulk Electrical Conductivity
Accuracy: ±5% from 0 to 5 dS/m, ±10% from 5 to 23 dS/m, user
calibration required above 10 dS/m
Resolution: 0.001 dS/m from 0 to 23 dS/m
Range: 0 to 25 dS/m (bulk)
Temperature
Accuracy: ±1◦C
Resolution: 0.1 ◦C
Range: -40 to 60 ◦C
General Specifications
Dimensions: 9.3 x 2.4 x 6.5 cm
Prong Length: 5.5 cm
Dielectric Measurement Frequency: 70 MHz
Measurement Time: 150 ms (milliseconds)
Power requirements: 3.6 to 15 VDC, 0.03 mA quiescent, 25 mA dur-
ing 150 ms measurement
2
GS3 1 INTRODUCTION
Output: Serial TTL, 3.6 Volt Levels or SDI-12
Operating Temperature: -40 to 60 ◦C1
Connector types: 3.5 mm (stereo) plug or stripped & tinned lead
wires (Pigtail)
Cable Length: 5 m standard; custom cable length available upon
request
1.3 Warranty
The GS3 has a one year warranty on parts and labor. The warranty
activates when the instrument arrives at your location.
Seller’s Liability
Seller warrants new equipment of its own manufacture against defec-
tive workmanship and materials for a period of one year from date of
receipt of equipment (the results of ordinary wear and tear, neglect,
misuse, accident and excessive deterioration due to corrosion from
any cause are not to be considered a defect); but Seller’s liability for
defective parts shall in no event exceed the furnishing of replacement
parts F.O.B. 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 prof-
its), occasioned by or arising out of the installation, operation, use,
misuse, nonuse, repair, or replacement of said material and equip-
ment, 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,
1Sensors can be used at higher temperatures. Please contact Decagon for
assistance.
3
1 INTRODUCTION GS3
the implied warranties of merchantability and fitness for a particular
purpose), not expressly set forth herein.
4
GS3 2 THEORY
2 Theory
2.1 Volumetric Water Content
The GS3 sensor uses an electromagnetic field to measure the dielec-
tric permittivity of the surrounding medium. The sensor supplies a
70 MHz oscillating wave to the sensor prongs that charges according
to the dielectric of the material. The stored charge is proportional to
substrate dielectric and substrate volumetric water content. The GS3
microprocessor measures the charge and outputs a value of dielectric
permittivity from the sensor. The dielectric value is then converted
to substrate water content by a calibration equation specific to the
media you are working in.
2.2 Temperature
The GS3 uses a small thermistor to take temperature readings. It is
located underneath the sensor overmold, next to one of the prongs
so it remains in thermal equilibrium with the medium, and reads the
temperature of the prong surface.
The GS3 outputs temperature in ◦C unless otherwise stated in your
preferences file in either the DataTrac 3 or ECH2O Utility programs.
It is important to note that even though the sensor head is white,
if it is in direct sunshine, the temperature measurement may read
high. Exposure of the sensor head to direct UV radiation may also
degrade the vinyl surface and cause it to discolor.
Use caution when installing the sensor with the overmold in the sun.
2.3 Electrical Conductivity
Electrical conductivity (EC) is the ability of a substance to conduct
electricity and can be used to infer the amount of polar molecules that
are in solution. EC is measured by applying an alternating electri-
cal current to two electrodes, and measuring the resistance between
5
2 THEORY GS3
them. Conductivity (referred to as “bulk electrical conductivity”)
is derived by multiplying the inverse of the resistance (conductance)
by the cell constant (the ratio of the distance between the electrodes
to their area). GS3 bulk EC measurements are normalized to EC at
25 ◦C We factory calibrate the bulk EC measurement to be accurate
within ±10% from 0 to 10 dS/m. This range is adequate for most
greenhouse and nursery applications.
However, some special applications in highly saline substrates may
require measurements with bulk EC greater than the specified range.
The GS3 will measure up to 23 dS/m bulk EC, but user calibration
is required above 10 dS/m. Additionally, EC measurements above
10 dS/m are very sensitive to contamination of the electrodes by skin
oils, etc. Be sure to read the sensor cleaning section at the end of
the manual if you plan to measure the EC of salty soils.
2.4 Converting Bulk EC to Pore EC
For many applications, it is advantageous to know the electrical con-
ductivity of the solution contained in the soil pores (σp), which is
a good indicator of the solute concentration in the soil. Tradition-
ally, σphas been obtained by extracting pore water from the soil and
measuring σpdirectly. As one would expect, this is a time consuming
and labor intensive process.
The GS3 measures the electrical conductivity of the bulk soil sur-
rounding the sensors (σb). A considerable amount of research has
been conducted to determine the relationship between σband σp.
Work by Hilhorst (2000), has taken advantage of the linear relation-
ship between the soil bulk dielectric permittivity (εb) and σbto allow
accurate conversion from σbto σpif the εbis known. The GS3 mea-
sures εband σbnearly simultaneously in the same soil volume. It is
therefore well suited to this method.
The pore water conductivity can be determined from (see Hilhorst,
2000 for derivation):
σp=pσp
b−σb=0
(1)
6
GS3 2 THEORY
where σpis the pore water electrical conductivity (dS/m); εPis
the real portion of the dielectric permittivity of the soil pore wa-
ter (unitless); σbis the bulk electrical conductivity, (dS/m), which is
measured directly by the GS3; εbis the real portion of the dielectric
permittivity of the bulk soil (unitless); εσb=0 is the real portion of the
dielectric permittivity of the soil when bulk electrical conductivity is
0 (unitless). εcan be calculated from soil temperature using:
εp= 80.3−0.37 ∗(Tsoil −20) (2)
where Tsoil is the soil temperature (◦C) measured by the GS3.
Finally, εσb=0 is an offset term loosely representing the dielectric per-
mittivity of the dry soil. Hilhorst (2000) recommended that εσb=0 =
4.1 be used as a generic offset. However, our research in several agri-
cultural soils, organic, and inorganic growth media indicates that
εσb=0 = 6 results in more accurate determinations of σp. Hilhorst
(2000) offers a simple and easy method for determining for individ-
ual soil types, which will improve the accuracy of the calculation of
σpin most cases.
Our testing indicates that the above method for calculating σpresults
in good accuracy (±20%) in moist soils and other growth media. In
dry soils where VWC is less than about 0.10 m3/m3, the denomi-
nator of equation 1 becomes very small, leading to large potential
errors. We recommend that p not be calculated in soils with VWC
<0.10 m3
m3using this method.
2.5 Pore Water vs. Solution EC
As noted in the previous section, pore water electrical conductivity
can be calculated from bulk EC using the sensor-measured dielec-
tric permittivity of the medium. However, pore water EC is not the
same as solution EC. Pore water EC is the electrical conductivity
of the water in the pore space of the soil. One could measure this
directly if the soil was squeezed under high pressure to force water
out of the soil matrix and that water was collected and tested for
EC. Solution EC is the electrical conductivity of pore water removed
from a saturated paste. In this case, the soil is wetted with distilled
7
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