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

Email: supp[email protected] or [email protected]

Trademarks

2011-2014 Decagon Devices, Inc.

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:

supp[email protected] or [email protected]

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 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

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.

1 INTRODUCTION GS3

the implied warranties of merchantability and ﬁtness for a particular

purpose), not expressly set forth herein.

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

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)

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

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