Moisture, salinity (electrical conductivity), temperature and wetting front in a single SDI-12 sensor
The GroPoint™ Pro soil sensor is robust, reliable and highly accurate, providing cost-effective measurement of soil moisture, soil temperature, salinity (electrical conductivity or EC).
This SDI-12 sensor also functions as a wetting front detector, providing a separate output for the wetting front measurement. By placing the tip of the sensor just above the bottom of your crop’s root zone, the wetting front measurement will indicate when water has reached the bottom of the probe during irrigation, allowing you to have your irrigation stop at precisely the optimal time to ensure only the water needed is applied.
The sleek, lightweight design installs quickly with minimal soil disruption. When installed vertically, the sensor averages volumetric moisture content over a soil layer of about 6” (15cm). When installed horizontally, the sensor can be used to measure moisture at a specific soil depth.
GroPoint Pro can be deployed in irrigation-sensitive zones, such as around the root zone, to enable full control of precision irrigation needs.
|Measurement range||0% to 100% of VMC|
|Measurement range||0 to 4 dS/m|
|Measurement range||-20°C to +70°C (-4°F to 158°F)|
|Output parameter||0 to 10, corresponding to rate of change of moisture from last reading|
Optional EN3 4-pin IP66/IP68 rated environmental connector
|Input voltage||6 to 14 VDC, max. 18 VDC|
|Current consumption||Quiescent: Active: 15-35 mA|
|Operating temperature||-20°C to 70°C (-4°F to 158°F)|
|Storage temperature||-40°C to 85°C (-40°F to 185°F)|
|Dimensions||19.6 cm x 2.0 cm x 0.56 cm (7.7” x 0.8” x 0.2”)|
|Weight (with standard cable)||272 g (0.6 lb.)|
|Cable weight||38 g per m (0.42 oz. per foot)|
|Standard cable||5 m (16.40 ft.)
4xAWG22 dual-shielded, twisted pair, rated for direct burial
|Warranty||1-year limited parts and labour|
* 8% to 42% VMC, in controlled laboratory conditions; factory calibrated for most agricultural soils. In field applications, accuracy may slightly decrease due to the inevitable heterogeneity of soil texture, soil compaction, moisture and fluctuation in soil temperature. The accuracy may also decrease in difficult soil conditions (higher clay and salinity content). In normal conditions, GroPoint sensors will maintain their accuracy from permanent wilting through field capacity in sandy loam through clay soils with less than 60% clay particles. Under moderately saline conditions. GroPoint sensors will maintain their accuracy up to 6 ds/m.
GroPoint Profile and GroPoint Pro will work with virtually any data logger that supports the SDI-12 standard.
GroPoint Lite and Classic will work with virtually any data logger. Just ensure your data logger will handle the output of your GroPoint Lite sensor (whether analog or digital).
By placing the tip of the sensor just above the bottom of your crop’s root zone (the wetting front sensor is at the tip of the probe), the wetting front measurement will indicate when water has reached the bottom of the probe during irrigation, allowing you to have your irrigation stop at precisely the optimal time to ensure only the water needed is applied.
The GroPoint Pro calculates the first derivative (rate of change) of moisture to indicate how quickly the moisture level is increasing (it does not indicate in any way moisture decreases). Range is 0 (very low or negative rate of change) to 10 (high rate of change). A slow moisture increase generates low values, whereas a very rapid moisture increase generates higher readings (up to the maximum of 10). It is not related to absolute moisture level, rather how quickly the moisture level is changing. There is no time element in this measurement, it just compares previous readings to the current reading.
For example, assuming dry to saturated step change, wetting front readings will appear similar to this over time:
0 – no moisture change
0 – no moisture change
1 – minor increase in moisture level
10 – sudden increase in moisture level
7 – no moisture change (already at high level) or moisture drops
4 – no moisture change (already at high level) or moisture drops
1 – no moisture change (already at high level) or moisture drops
0 – no moisture change (already at high level) or moisture drops
Important note: The sensor must be continuously powered to provide useful wetting front measurement, as it maintains historical data values used in its calculations which are lost if power is turned off.
No, GroPoint probes are meant to be used on a permanent or semi-permanent basis. There should be minimal disturbance of the surrounding soil for proper accuracy.
GroPoint probes can be used in virtually any soil.
- Can the sensor cable be buried, and is it durable enough to be left exposed on the surface of the ground?
GroPoint sensors are furnished with a high quality cable suitable for direct burial or exposure to direct sunlight. It is resistant to damage from insects, abrasion and normal environmental exposure. However, mechanical damage from hoes, coyotes, gophers, other animals, and cultivators can easily cut this cable. Any problem with this sensor will most likely be due to damage to the electrical cable. To prevent damage, it is strongly recommended that the cable be installed in 3/4-inch electrical conduit. This size conduit is required to accommodate the passage of the plug connector.
For SDI-12 sensors, according to the SDI-12 specification, the combined length of all sensors connected to a data logger cannot exceed 610 m (2,000 feet). So one sensor with a 610 m cable or 10 sensors each with a 61 m cable.
For analog sensors, the maximum length is 305 m (1,000 feet).
It should be noted that the longer the cable is, the more susceptible the sensor is to catastrophic damage/failure due to increased voltage spikes from lightning strikes. A long cable becomes a very large antenna to amplify the voltage. Cable should be buried wherever possible.
The minimum wire gauge when using a cable approaching the maximum should be 20 AWG.
Custom cable lengths can be ordered from us, or cable may be spliced by the customer. Each cable has three wires. The cable must be 22 gauge copper or larger.
All connections should be made inside a waterproof box using silicone filled, waterproof, wire nut connectors. These waterproof connectors are available at local electrical/hardware suppliers, such as The Home Depot.
GroPoint probes are factory-calibrated for use in most soils. There are also two other standard calibrations that can be used, which you can specify when you order. Below is an image of a standard soil texture triangle. By default, calibration is done for a wide variety of soil types represented by the red area. You can also request that your sensor is calibrated for clay or highly saline soil (the green area) or sandy soils (blue area).
Custom calibration can be done at our facility upon request. End customers can also perform their own calibration (documented in the User Manual).
If you’re using a sensor with the wrong calibration, measurements will have a small absolute/relative error, read either too high or too low by up to 4%.
GroPoint sensors feature an accuracy rating of ±2% (±0.02 m3m-3) volumetric soil moisture, between the range of 8% to 42% VMC (this is the normal range for agricultural applications). We obtain this accuracy through a patented technique which improves the performance of the already reliable TDT method of soil moisture measurement. This patented technology is called TDT5, which you can read about here.
While a < ±1% accuracy rating is achieved in controlled laboratory conditions, GroPoint sensors are factory calibrated for most agricultural soils. In field applications, accuracy may slightly decrease due to the inevitable heterogeneity of soil texture, soil compaction, moisture and fluctuation in soil temperature. The accuracy may also decrease in difficult soil conditions (higher clay and salinity content). For these reasons we state a real-world accuracy of ±2%. In normal conditions, GroPoint sensors will maintain this accuracy from permanent wilting through field capacity in sandy loam through clay soils with less than 60% clay particles. Under moderately saline conditions, GroPoint sensors will maintain their accuracy up to 6 ds/m.
TDT5 is a proprietary technology based on Time Domain Transmission (TDT), which is a refined version of Time Domain Reflectometry (TDR). TDT measures the time taken for an electromagnetic wave to propagate (travel) along a given length of a transmission line in the soil. Moisture in the soil changes the soil’s dielectric properties, so that the electromagnetic wave travels at different rates in wet soil compared to dry soil. This allows for the accurate determination of soil moisture content.
However, we add our own engineering designs that result in a less expensive, more robust and more accurate (with greater repeatability) sensor than with pure TDT alone. This enhances TDT in five (hence “TDT5“) key ways:
- Measures with an antenna 5 times longer than the physical length of the probe, which reduces the impact of noise, and provides an average across the entire length of each segment of the probe.
- Filtering 400,000 pulses for each measurement – boosts accuracy to ±2% and repeatability to < 0.2%
- Captures measurement in less than 100ms – reduces power consumption
- Embeds antenna and circuitry on a single board – dramatically reduces cost to manufacture
- Encases entire sensor in a durable, sealed polycarbonate housing – maximizes durability
The GroPoint Lite and GroPoint Pro measure the average soil moisture along its active length about 15 cm (6″), which is 3 cm (1.25″) from the top and 2.5 cm (1″) from the bottom of the sensor, whether the sensor is installed vertically or horizontally. Under most conditions, the sensor’s active range extends about 10 cm (4″) out from the side of the sensor, and 2.5 cm (1″) from the tip.
To request a quote, use the blue “Request a Quote” button (top right).
- Based on our unique TDT5 technology.
- Comes with 5 m (16.4′) durable cable (4-pin IP68-rated EN3 connector optional).
- Factory-calibrated for most agricultural soils, but can be custom calibrated before shipping—request when ordering.
- Low power consumption—suitable for remote applications.
Comes with 5 m (16.4′) durable cable (4-pin IP68-rated EN3 connector optional).
- Can be custom calibrated by the customer—see detailed procedure in the user manual (see Downloads section).