Decagon Devices GS3 User Manual

For support contact us via email at [e-mail]

or call us at 1.509.332.5600 between 7AM to 5PM PST

1

APPLICATIONS

 Greenhouse substrate monitoring.
 Volumetric water content measurement.
 Soil/Substrate water balance.
 Irrigation management.
 Electrical Conductivity measurement.
 Salt management.
 Fertilizer movement.
 Soil/Substrate temperature measurement.
 Modeling processes that are affected by

temperature.

DESCRIPTION

The Decagon GS3 sensor is an accurate tool for
monitoring electrical conductivity, volumetric water
content, and temperature in soil and soilless
substrates. The GS3 determines volumetric water
content (VWC) by measuring the dielectric constant

(εa) of the medium using capacitance / frequency-

domain technology. The sensor uses a 70 MHz
frequency, which minimizes textural and salinity
effects, making the GS3 accurate in most soilless
substrates. The GS3 measures temperature using
an onboard thermistor, and electrical conductivity
using a stainless steel electrode array.

For a more detailed description of how this sensor
makes measurements, refer to the User Manual.

AUDIENCE

Decagon provides the information in this integrators
guide to help GS3 customers establish
communication between these sensors and their
data acquisition equipment or field data loggers.
Customers using data loggers that support SDI-12
sensor communications should consult the user's
manual for their data logger. These sensors are fully
integrated into Decagon's system of plug-and-play
sensors, cellular-enabled data loggers, and data
analysis software.

ADVANTAGES

 Digital sensor communicates three

measurements over a serial interface.

 2-probe EC measurement.
 Robust thermistor for accurate temperature

measurements.

 Low input voltage requirements.
 Low power design supports battery-operated

data loggers.

 Robust epoxy encapsulation and stainless

steel needles to resist corrosive environments.

 Supports SDI-12 or DDI-Serial 1-wire serial

communications protocols.

 Modern design optimized for low-cost sensing.

Volumetric Water Content

Temperature

Electrical Conductivity

Accuracy

±1 εa (unitless) from 1 – 40 εa

±15% from 40 – 80 εa

Generic calibration equation:

± 0.03 m3/m3 (± 3% VWC)

Medium Specific Calibration:

± 0.02 m3/m3 (± 2% VWC)

± 1°C

± 5% from 0 to 5 mS/cm (dS/m)

± 10% from 0 to 5 – 25 mS/cm (dS/m)

user calibration required above:

25 mS/cm (dS/m)

Resolution

0.1 εa (unitless) from 1 – 20 εa
<0.75 εa from 20 – 80 εa

0.2% VWC from 0% – 40% VWC

0.1% VWC from 40% – 100% VWC

0.1°C

0.001 mS/cm (dS/m)

Range

1 εa – 80 εa

- 40°C to + 50°C

0 – 25 dS/m

GS3 Greenhouse Sensor

2365 NE Hopkins Ct / Pullman, WA 99163 USA Volumetric Water Content, Electrical Conductivity, and Temperature

MEASUREMENT SPECIFICATIONS

GS3 Integrator Guide R34

For support contact us via email at [e-mail]

or call us at 1.509.332.5600 between 7AM to 5PM PST

2

SENSOR IMAGE

SENSOR NAME

GS3 Greenhouse Sensor

DIMENSIONS

9.3 cm X 6.5 cm X 2.4 cm

CABLE LENGTH*

5 meters

PARAMETER

MIN

TYP

MAX

UNITS

Supply Voltage (VCC) to GND

3.6 15

V

Digital Input Voltage (logic high)

2.8 3 3.9

V

Digital Input Voltage (logic low)

-0.3 0 0.8

V

Power Line Slew Rate

1

V/mS

Current Drain (during measurement)

0.5 3 30

mA

Current Drain (while asleep)

0.03 mA

Operating Temperature Range

-40 50

°C

Power Up Time (DDI-Serial)

100

mS

Power Up Time (SDI-12)

100

150

200

mS

Measurement duration

150

200

mS

Cable Capacitance / meter

250 pF

Cable Resistance / meter

35 mΩ

NOTE: This is a low impedance variant of the recommended SDI-12
Specification. This allows up to 62 sensors to be maintained on a bus.

PIGTAIL CABLE

STEREO CABLE

Data

Power

Ground

Data

Power

Ground

PHYSICAL CHARACTERISTICS

* Custom cable lengths are available for an additional cost.

ELECTRICAL AND TIMING CHARACTERISTICS

EQUIVALENT CIRCUIT DIAGRAM CONNECTION TYPES

GS3 Integrator Guide R34

For support contact us via email at [e-mail]

or call us at 1.509.332.5600 between 7AM to 5PM PST

3

SAFETY PRECAUTIONS

Our probes are built to the highest standards but misuse or improper protection or improper installation

may break your sensor and possibly void the manufacturer’s warranty. Before integrating your sensors

into your sensor network, make sure you have followed the recommended installation instructions and
have the proper protections in place to safeguard your sensor from damaging interference.

LIGHTNING AND SURGE PROTECTION

Probes have built in circuitry that protects them against common surge conditions. Installations in
lightning-prone areas, however, require special precautions, especially when probes are connected to a
well-grounded third party logger.

Visit our website and read the following application note for more information:

Lightning Surge Suppression And Standard Grounding Practices

POWER AND GROUNDING

Older sensor versions start measurements as soon as they are powered. For older sensors, ensure that
there is sufficient power to support the maximum sensor current drain for all the sensors on the bus
simultaneously.

Our sensor protection circuitry may be insufficient if your data logger is improperly powered or grounded.

Refer to your data logger’s installation instructions. Improper grounding may affect the sensor output as

well as the sensor performance.

For Decagon loggers, visit our website and read the following article for more information:

Lightning Surge Suppression And Standard Grounding Practices

CABLE PROBLEMS

Cable problems can lead to severed cables or disconnected sensors. Rodent damage, driving over sensor
cables, tripping over the cable, not leaving enough cable slack during installation or poor sensor wiring
connections are just some of many factors that can cause cabling issues.

GS3 Integrator Guide R34

For support contact us via email at [e-mail]

or call us at 1.509.332.5600 between 7AM to 5PM PST

4

SENSOR COMMUNICATION TYPES

Decagon digital sensors feature a 1-wire serial interface for communicating sensor measurements. The
sensor supports two different protocols: SDI-12 and DDI-Serial. Both interfaces are documented in this
guide. Each protocol has advantages and implementation challenges. There are differences in voltage
levels, logic levels, and signal timing for each protocol. Please contact Decagon with your specific
requirements if the protocol choice for your application is not obvious.

SDI-12 INTRODUCTION

SDI-12 is a standards-based protocol for interfacing sensors to data loggers and data acquisition
equipment. Multiple sensors with unique addresses can share a common 3-wire bus (power, ground, and
data). Two-way communication between the sensor and logger are possible by sharing the data line for
transmit and receive as defined by the standard. Sensor measurements are triggered by protocol
command.

DDI-SERIAL INTRODUCTION

The DDI-Serial protocol is the method used by the Decagon's family of data loggers for collecting data from
the sensor. This protocol uses the data line configured to transmit data from the sensor to the receiver
only (simplex). Typically the receive side is a microprocessor UART or a general-purpose IO pin using a "bit­bang" method to receive data. Sensor measurements are triggered by applying power to the sensor.

INTERFACING THE SENSOR TO A PC

The serial signals and protocols supported by the sensor require some type of interface hardware to be
compatible with the serial port found on most personal computers (or USB-to-Serial adapters). There are
several SDI-12 interface adapters available in the marketplace; however, Decagon has not tested any of
these interfaces and cannot make a recommendation of which adapters work with Decagon sensors.
Decagon's Em50 data logger and ProCheck hand-held both are able to operate as a computer-to-sensor
interface for making on-demand sensor measurements.