Decagon Devices GS3 User Manual

GS3 Greenhouse Sensor
2365 NE Hopkins Ct / Pullman, WA 99163 USA Volumetric Water Content, Electrical Conductivity, and Temperature
For support contact us via email at support@decagon.com
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
(ε
a
) 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.
MEASUREMENT SPECIFICATIONS
Volumetric Water Content
Temperature
Electrical Conductivity
Accuracy
±1 ε
a
(unitless) from 1 – 40 ε
a
±15% from 40 – 80 ε
a
Generic calibration equation:
± 0.03 m
3
/m
3
(± 3% VWC)
Medium Specific Calibration:
± 0.02 m
3
/m
3
(± 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 ε
a
(unitless) from 1 – 20 ε
a
<0.75 ε
a
from 20 – 80 ε
a
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 ε
a
– 80 ε
a
- 40°C to + 50°C
0 – 25 dS/m

Decagon Devices GS3 Specifications

General

Weight	140 g
Dimensions	7.5 cm x 3.5 cm x 1.5 cm
Temperature Accuracy	±1 °C
Temperature Resolution	0.1 °C
EC Resolution	0.01 dS/m
Connector Type	3.5 mm stereo plug
Measurement Type	Soil moisture, temperature, and electrical conductivity (EC)
Soil Moisture Accuracy	±3%
Soil Moisture Range	0 to 100% VWC
EC Accuracy	±10%
Operating Temperature	-40°C to 60°C
Cable Length	5 m standard
Output	Analog
Power Supply	3.6–15 VDC
Current Drain	10 mA

Summary

Sensor Applications

Sensor Advantages

GS3 Greenhouse Sensor Description

Target Audience

Physical Characteristics

Electrical and Timing Characteristics

Connection Types

Pigtail Cable

Describes the pigtail cable connection option for the sensor.

Stereo Cable

Describes the stereo cable connection option for the sensor.

Safety Precautions

Lightning and Surge Protection

Guidance on protecting the sensor from lightning and power surges.

Power and Grounding

Recommendations for proper power supply and grounding of the sensor.

Cable Problems

Discussion of potential issues related to sensor cable integrity and connections.

Sensor Communication Types

SDI-12 Introduction

Overview of the SDI-12 standard protocol for sensor interfacing.

DDI-Serial Introduction

Explanation of the DDI-Serial protocol for data collection.

Interfacing the Sensor to a PC

Information on connecting the sensor to a personal computer for data acquisition.

SDI-12 Communication

Decagon's SDI-12 Implementation

Details on how Decagon implements the SDI-12 standard for its sensors.

Sensor Bus Considerations

Factors to consider when setting up and maintaining SDI-12 sensor networks.

SDI-12 Timing

Common SDI-12 Commands

Info Command (a i!)

Command to retrieve detailed information about a sensor on the bus.

Measurement Command (a M!)

Command to initiate a sensor measurement and retrieve data.

Data Command (a D 0!)

Change Address Command (a a b !)

Address Query Command (? !)

DDI-Serial Communication

DDI-Serial Timing

Details on the timing and data transmission for the DDI-Serial protocol.

DDI-Serial Response

DDI-Serial Checksum