Decagon Devices 5TE Operator's Manual

5TE

Water Content, EC

and Temperature Sensors

Operator’s Manual

Ve rsio n 2

©2008 Decagon Devices, Inc.

All rights reserved.

Decagon Devices, Inc.

2365 NE Hopkins Court

Pullman WA 99163

www.decagon.com

5TE Operator’s Manual

Table of Contents

Contents

1. Introduction . . . . . . . . . . . . . . . . . .1

Specifications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1

Contact Information . . . . . . . . . . . . . . . . . . . . . . . . . 2

Warranty Information . . . . . . . . . . . . . . . . . . . . . . . 3

Seller’s Liability . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3

2. About the 5TE . . . . . . . . . . . . . . . . 4

Background Info . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4

3. Theory . . . . . . . . . . . . . . . . . . . . . 6

Volumetric Water Content . . . . . . . . . . . . . . . . . . . 6

Temperature . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6

Electrical Conductivity . . . . . . . . . . . . . . . . . . . . . . . 7

Converting Bulk EC to Pore EC . . . . . . . . . . . . . . 8

Pore Water vs. Solution EC . . . . . . . . . . . . . . . . . . . 9

4. Calibration . . . . . . . . . . . . . . . . . . 11

Dielectric Permittivity . . . . . . . . . . . . . . . . . . . . . . . . 11

Mineral Soil Calibration . . . . . . . . . . . . . . . . . . . . . 11

Calibration in Non-Soil Media . . . . . . . . . . . . . . . 12

5. Connecting Sensors . . . . . . . . . . .13

Using the 5TE with Em50/50R data loggers. . . . 13

3.5mm Stereo Plug Wiring . . . . . . . . . . . . . . . . . . . 14

Extending sensor cables . . . . . . . . . . . . . . . . . . . . . 14

Connecting to a non-Decagon Data logger . . . . . 15

Logger Communications . . . . . . . . . . . . . . . . . . . . . 16

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5TE Operator’s Manual

Table of Contents

Dielectric Permittivity . . . . . . . . . . . . . . . . . . . . . . . 17

Electrical Conductivity . . . . . . . . . . . . . . . . . . . . . . 17

Temperature . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18

6. Installing the Probes . . . . . . . . . .19

Procedure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19

Orientation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21

Removing the Probes . . . . . . . . . . . . . . . . . . . . . . . 21

Multiple Probe Installation . . . . . . . . . . . . . . . . . .22

7. Campbell Scientific Programs . . 23

8. Troubleshooting&Sensor Care . 24

Datalogger . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .24

Probes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .24

Sensor Cleaning . . . . . . . . . . . . . . . . . . . . . . . . . . .25

Cleaning Method . . . . . . . . . . . . . . . . . . . . . . . . . . .26

Declaration of Conformity . . . . . . 27

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5TE Operator’s Manual

1. Introduction

1. Introduction

Thank you for choosing Decagon’s 5TE for measuring water
content, temperature, and EC. This manual is designed to help
you understand the probe’s features and how to use this
device successfully.

Specifications

Volumetric water content:

Range:

Apparent dielectric permittivity (εa): 1 (air) to 80 (water)
Resolution:

ε

: 0.1

ε

a

(unitless) from 1-20, <0.75

a

ε

(unitless) from 20-80

a

VWC: 0.0008 m3/m3 (0.08% VWC) from 0 to 50% VWC

Accuracy:

(

ε

): ±1

a

ε

(unitless) from 1-40 (soil range), ±15% from 40-80

a

(VWC):

• Using Topp equation: ±0.03 m3/m3 (±3% VWC) typical
in mineral soils that have solution electrical conductivity <
10 dS/m

• Using medium specific calibration, ±0.01 - 0.02 m

3/m3

(± 1-2% VWC) in any porous medium

Electrical Conductivity (bulk):

Range: 0-23 dS/m (bulk)
Resolution: 0.01 dS/m from 0 to 7 dS/m, 0.05 dS/m from 7

to 23 dS/m
Accuracy: ±10% from 0 to 7 dS/m, user calibration required
above 7 dS/m

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5TE Operator’s Manual

1. Introduction

Temperature

Range: -40-50 °C
Resolution: 0.1 °C
Accuracy: ±1 °C

General

Dimensions: 10 cm (1) x 3.2 cm (w) x 0.7 cm (d)
Prong Length: 5.2 cm
Dielectric Measurement Frequency: 70 MHz
Measurement Time: 150 ms (milliseconds)
Power requirements: 3.6 - 15 VDC, 0.3 mA quiescent, 10

mA during 150 ms measurement
Output: RS232 or SDI 12 (contact Decagon for information
on SDI-12 mode)

Operating Temperature: -40-50 °C
Connector types: 3.5 mm “stereo” plug or stripped and

tinned lead wires
Cable Length: 5m standard; custom cable length available
upon request

Datalogger Compatibility (not exclusive):

Decagon: Em50, Em50R
Campbell Scientific: Any logger with serial I/O (CR10X,
CR850, 1000, 3000, etc.)

Contact Information

If you need to contact Decagon:

• Call us at 800-755-2751 or [phone]

• Fax us at [phone]

• E-mail us at [e-mail].

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5TE Operator’s Manual

1. Introduction

Warranty Information

All Decagon products have a 30-day satisfaction guarantee
and a one-year warranty.

Seller’s Liability

Seller warrants new equipment of its own manufacture against
defective 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
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.

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5TE Operator’s Manual

2. About the 5TE

2. About the 5TE

The 5TE is designed to measure the water content, electrical
conductivity, and temperature of soil and growing media.
Using an oscillator running at 70 MHz, it measures the dielec­tric permittivity of soil to determine the water content. A ther­mistor in thermal contact with the probe prongs provides the
soil temperature, while the screws on the surface of the sensor
form a two-probe electrical array to measure electrical con­ductivity.

Background Info

In 2006, Decagon incorporated research from its EC-5 volu­metric water content sensor into the ECH2O-TE, a sensor
which measured volumetric water content, temperature, and
electrical conductivity. The new 5TE uses the same theory as
the ECH2O-TE, but the location of the EC measurement is in
the stainless steel screws instead of gold traces. The use of
stainless steel screws has made the 5TE a more robust sensor.
Additionally, the 5TE utilizes a 5 point dielectric calibration to
provide dielectric permittivity measurements far more accu­rate than the previous ECH

O-TE.

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5TE Operator’s Manual

2. About the 5TE

Figure 1: 5TE Components

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5TE Operator’s Manual

3. Theory

3. Theory

Volumetric Water Content

The 5TE probe uses an electromagnetic field to measure the
dielectric permittivity of the surrounding medium. The probe
supplies a 70 MHz oscillating wave to the probe prongs that
charges according to the dielectric of the material. The stored
charge is proportional to soil dielectric and soil volumetric
water content. The 5TE microprocessor measures the charge
and outputs a value of dielectric permittivity from the probe.

Temperature

The 5TE uses a surface-mounted thermistor to take tempera­ture readings. It is located underneath the probe overmold,
next to one of the prongs, and will read the temperature of the
prong surface. The 5TE will output temperature in °C unless
otherwise stated in your preferences file in either the ECH2O
DataTrac or ECH2O Utility programs.

It is important to note that if the black plastic overmold of the
probe is in direct sunshine, the temperature measurement may
read high. Exposure of the overmold to solar radiation will
also drastically decrease the life expectancy of the sensor. We
do not recommend that the sensor be installed with the over­mold in the sun.

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5TE Operator’s Manual

3. Theory

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 electrical current to two electrodes, and
measuring the resistance between them. Conductivity is then
derived by multiplying the inverse of the resistance (conduc­tance) by the cell constant (the ratio of the distance between
the electrodes to their area).

The 5TE uses a 2-probe array to measure the EC. The array is
located on the screws of two of the 5TE prongs. Small

amounts of oil from skin contact with the screws will
cause significant inaccuracy in the EC measurement. See

the sensor cleaning section at the end of this manual for
instructions on cleaning the probes if contamination occurs.

The 5TE uses a two electrode array to measure the bulk EC of
the surrounding medium. The bulk EC measurement is cali­brated at the factory to be accurate within ±10% from 0 to 7
dS/m. This range is adequate for most field, greenhouse and
nursery applications. However, some special applications in
salt affected soils may requires measurements with bulk EC
greater than the specified range. The 5TE will measure up to

23.1 dS/m bulk EC, but user calibration is required above 7

dS/m. Additionally, EC measurements above 7 dS/m are very
sensitive to contamination of the electrodes by skin oils, etc.
Be sure to read sensor cleaning section at the end of the man­ual if you plan to measure the EC of salty soils.

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