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Enabling better global research outcomes in soil, plant & environmental monitoring.

Decagon GS3 VWC, Temp + EC

A moisture sensor for mineral soils and soilless substrates such as rockwool, potting soil, peat, and perlite. Suitable for both field and greenhouse use.

The GS3 soil moisture, temperature, and EC sensor is the newest sensor in the Decagon system.

The GS3 measures water content, temperature, and bulk electrical conductivity. Its stainless steel needles have an extended surface area to optimise EC measurements and minimise substrate disturbance during insertion. The GS3 comes standard with both serial and SDI-12 communication; you can plug and log with Decagon data loggers or integrate with other systems.

GS3 Soil Moisture Sensor Features
Accuracy at a Fraction of the Cost

The GS3 measures water content, temperature, and EC independently. Its 70 MHz frequency minimises salinity and textural effects, making it accurate in most soil or soilless media. Stainless steel needles have an extended surface area to optimise EC measurements, while minimising substrate disturbance during insertion. Temperature is measured with an onboard thermistor, and electrical conductivity is measured using a stainless steel electrode array.

Understand Your Measurements
When used in conjunction with our DataTrac 3 software, your GS3 data can be used to determine plant available water, growing degree days, and pore water electrical conductivity.

Integrate with Data Loggers
Each GS3 comes standard with both serial and SDI-12 communication options.

GS3 SOIL SENSOR

ACCURACY VWC: Using a generic calibration: ± 0.03 m3 /m3 (± 3% VWC) typical in mineral soils that have solution electrical conductivity less than 10 dS/m; Using medium specific calibration, ± 0.01 – 0.02 m3 /m3 (± 1-2% VWC) in any porous medium.
Electrical Conductivity: ± 10% from 0 to 10 dS/m, user calibration required above 10 dS/m Temperature: ± 1°C
RESOLUTIONS Using Topp equation: ± 0.03 m3/m3 (± 3% VWC) typical in mineral soils that have solution electrical conductivity less than 10 dS/m. Using medium specific calibration, ± 0.02 m3/m3 (± 2% VWC) in any porous medium.
SENSOR TYPE VWC: Frequency domain, EC: Two probe design, Temperature: Thermistor
OPERATING ENVIRONMENT -40°C to 80°C
RANGE VWC: 0 – 100% EC: 0 – 23 dS/m (bulk)
DIMENSIONS 9.3 cm x 2.4 cm x 6.5 cm
CABLE LENGTH 5 m standard, custom cable lengths available upon request
MEASUREMENT TIME 150 ms (milliseconds)
POWER 3.6 – 15 VDC, 0.3 mA quiescent, 25 mA during 150 ms measurement
CONNECTOR TYPES 3.5mm “stereo” plug, or stripped and tinned lead wires (3)
OUTPUT Serial TTL, 3.6 Volt Levels or SDI-1
DATALOGGER COMPATIBILITY (not exclusive) Decagon: Em50, Em50R, Em50G, ProCheck or Any data acquisition system capable of 3.6-15V excitation and serial or SDI-12 communication

SENSOR COMPARISON TABLE

ANALOG SENSORS DIGITAL SENSORS
SENSOR EC-5 10HS 5TM 5TE GS3 MPS-2
MEASURES volumetric water content, dielectric permittivity volumetric water content, dielectric permittivity volumetric water content, dielectric permittivity, temperature volumetric water content, dielectric permittivity, temperature, electrical conductivity volumetric water content, dielectric permittivity, temperature, electrical conductivity water potential,
temperature
VOLUME OF INFLUENCE 0.3 L 1 L 0.3 L 0.3 L 0.3 L N/A
DATA LOGGER COMPATIBILITY Em5b, Em50, Em50R, Em50G, ProCheck, ECH2O Check, Campbell Scientific* Em5b, Em50, Em50R, Em50G, ProCheck, ECH2O Check, Campbell Scientific*

Em50, Em50R, Em50G, ProCheck, Campbell Scientific*, SDI-12 capable

Em50, Em50R,  Em50G, ProCheck, SDI-12 capable

Em50, Em50R, Em50G, ProCheck, SDI-12 capable

Em50, Em50R, Em50G, ProCheck, SDI-12 capable

MEASUREMENT RANGE 0 to 100% VWC 0 to 57% VWC

0 to 100% VWC

-40 to 50°C

0 to 100% VWC

-40 to 50°C

0 to 23 dS/m

0 to 100% VWC

-40 to 80°C

0 to 23 dS/m

-10 to -500 kPa (pF 2 – pF 3.71)

-40 to 50°C

BEST IF VWC is all that you need.You’re establishing a large sensor network. You want a large volume of influence.

You have high temperature variability in your soils.

You are monitoring shallow or desert soils where data must be corrected for temperature effects.

You need to monitor soil temperature for biological activities.

You want to use SDI-12.

You are managing salts in your system.You want to use SDI-12.

You are measuring water content of soilless substrates.

You need high accuracy EC.

You need to measure at high temperatures

You want to compare soil moisture at different research sites.

You want to determine water available for plant growth.

You are monitoring deficit irrigation.

You want to measure water potential.

BUT NOT IF You cannot apply a regulated voltage (to non-Decagon data loggers). You are measuring in nursery pots.You are installing in rocky soil.  N/A You want to monitor soiless substrates or potting soils. You are doing downhole installations. You want to monitor soils at or near saturation.

Volumetric Water Content

The GS3 sensor uses an electromagnetic field to measure the dielectric 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.

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 will read the temperature of the prong surface. The GS3 will output 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 causing it to discolour. Use caution when installing the sensor with the overmold in the sun.

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 (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). The bulk EC measurement is calibrated at the factory 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.