Long Lasting Accurate Soil Monitoring With A Wireless Sensor Network

A wireless sensor that works with the HOBOnet system to not only provide advanced soil moisture measurements (volumetric water content) with better accuracy and precision, but also measure soil temperature and electrical conductivity. Designed to withstand harsh environmental conditions, this durable sensor last up to 10 years, so you can leave them in the field for extended periods of time. Sharpened stainless-steel probe tips make installation easy, even in hard soil, and an increased volume of influence provides more accurate results. The HOBOnet T12 is backed by over 20 years of soil-moisture research and features a trademark 70MHz frequency capacitance technology, minimizing salinity and textural effects.

The HOBOnet system is a cost-effective and scalable wireless sensor network for web-enabled monitoring of field conditions for applications such as crop management, research, and greenhouse operations. And because it’s wireless, you can deploy a network of sensors to easily monitor multiple points with a single system, while avoiding the risk of long cables that can interfere with field operations and are potentially vulnerable to nearby lightning strikes. Sensors are easily linked to the network, and data can be accessed through HOBOlink®, Onset’s innovative cloud software platform.

We recommend using the Verification Clip (see Compatible Items, below). The Verification Clip provides a convenient way to confirm the operation and soil-moisture accuracy of HOBOnet T11 and T12 sensors. Attaching this clip to a sensor provides a known soil moisture level for verifying measurement accuracy, without having to test the sensor in actual soils, which normally requires weighing soil samples and drying them in an oven.

Features

Sensor Features

• Soil moisture (volumetric water content), soil temperature, and electrical conductivity measurements with one device
• Sensor lasts up to 10 years in the field
• Largest volume of influence (1010 mL) relative to sensor size, resulting in more accurate soil moisture measurements
• Easy installation with sharpened stainless-steel probes that are more resistant to damage/deterioration
• Less sensor-to-sensor variability

Wireless Features

• 900 MHz wireless mesh self-healing technology
• 450 to 600 meter (1,500 to 2,000 feet) wireless range and up to five hops
• Up to 50 wireless sensors or 336 data channels per HOBO RX station
• Simple button-push to join the HOBOnet wireless network
• Onboard memory to ensure no data loss
• Powered by rechargeable AA batteries and built-in solar panel

Important Information

A complete system requires at least one HOBO RX3000 Remote Monitoring Station, a HOBOnet Wireless Manager, and a HOBOnet Wireless Sensor, OR one HOBO MicroRX station (which has an integrated HOBOnet Wireless Manager) and a HOBOnet Wireless Sensor. HOBOnet Wireless Repeaters (RXW-RPTR-xxx or RXW-RPTR-B-xxx) can be added to extend the range.

 

Soil Moisture: Volumetric Water Content (VWC)
Measurement Range*	0.00 to 0.70 m³/m³ in mineral soils
Accuracy	±0.030 m³/m³ (±3%) typical from 0 to 50°C (32 to 122°F); ±0.020 m³/m³ (±2%) with soil specific calibration
Resolution	0.001 m³/m³
Dielectric Measurement Frequency	70 MHz
Temperature**
Measurement Range	-40 to 60°C (-40 to 140°F)
Accuracy	±0.5°C (0.9°F) from -40 to 0°C (-40 to 32°F) ±0.3°C (0.54°F) from 0 to 60°C (32 to 140°F)
Resolution	0.1°C (0.18°F)
Bulk Electrical Conductivity (EC)
Measurement Range	0 to 20 dS/m (bulk)
Accuracy	±5% of reading + 0.01 dS/m from 0 to 10 dS/m ±8% of reading from 10 to 20 dS/m
Resolution	0.001 dS/m
Wireless Mote
Operating Temperature Range	Sensor: -40 to 60°C (-40 to 140°F) Mote: -25° to 60°C (-13° to 140°F) with rechargeable batteries -40 to 70°C (-40 to 158°F) with lithium batteries
Radio Power	12.6 mW (+11 dBm) non-adjustable
Transmission Range	Reliable connection to 457.2 m (1,500 ft) line of sight at 1.8 m (6 ft) high Reliable connection to 609.6 m (2,000 ft) line of sight at 3 m (10 ft) high
Wireless Data Standard	IEEE 802.15.4
Radio Operating Frequencies	RXW-T12-900: 904–924 MHz RXW-T12-868: 866.5 MHz RXW-T12-921: 921 MHz RXW-T12-922: 916–924 MHz
Modulation Employed	OQPSK (Offset Quadrature Phase Shift Keying)
Data Rate	Up to 250 kbps, non-adjustable
Duty Cycle	<1%
Maximum Number of Motes	50 motes per one HOBOnet Wireless Sensor Network
Battery Type/ Power Source	Two AA 1.2V rechargeable NiMH batteries, powered by built-in solar panel or two AA 1.5 V lithium batteries for operating conditions of -40 to 70°C (-40 to 158°F)
Battery Life	With NiMH batteries: Typical 3–5 years when operated in the temperature range -20° to 40°C (-4°F to 104°F) and positioned toward the sun (see Deployment and Mounting), operation outside this range will reduce the battery service life With lithium batteries: 1 year, typical use
Memory	16 MB
Dimensions	Sensor: 7.47 x 9.4 x 2.39 cm (2.94 x 3.7 x 0.94 inches) Sensor needle length: 5.4 cm (2.13 inches) Sensor needle diameter: 0.32 cm (0.13 inches) Cable length: 5 m (16.4 ft) Mote: 16.2 x 8.59 x 4.14 cm (6.38 x 3.38 x 1.63 inches)
Weight	RXW-T12-xxx sensor and cable: 245 grams (8.64 oz) Mote: 223 g (7.87 oz)
Materials	Sensor: ASA plastic body with polyurethane epoxy filling and stainless steel pins Cable: PVC, UV resistant and rodent repellent Mote: PCPBT, silicone rubber seal
Environmental Rating	Mote: IP67, NEMA 6
Compliance Marks	See User Manual

* The sensor data can be post-calibrated if necessary (e.g. the sensor is used in non-mineral soil types or higher than standard accuracy is required). Users can apply a calibration equation to the data exported from HOBOlink. The VWC range will depend on the calibration equation.

** Temperature measurement, for applicable sensors, may not be accurate if sensor is not fully immersed in medium of interest, due to longer equilibration time.

Is calibration required for different soil types? And if so, how is calibration done?

HOBOnet TEROS 11 and TEROS 12 soil moisture sensors come calibrated for most soil types. However, for soil types with high sand or salt content, the standard calibration may not be accurate. In such cases, soil-specific calibration should be used.

To determine the soil-specific calibration formula, please refer to: https://www.onsetcomp.com/support/tech-notes/calibrating-ech2o-soil-moisture-sensors-application-note

Please note too that because the HOBOnet TEROS 21 sensor measures soil water potential, it does not require soil-specific calibration.