Delta-T Devices WET-2 Portable Soil Moisture, Temperature & Electrical Conductivity Sensor
| Brand | Delta-T Devices |
|---|---|
| Origin | United Kingdom |
| Model | WET-2 |
| Type | Multi-parameter Soil Analyzer |
| Measurement Principle | Frequency Domain Reflectometry (FDR) |
| EC Range | 0–300 mS·m⁻¹ (default), extendable to 0–600 mS·m⁻¹ via calibration |
| Temp Range | −5 to +50 °C |
| Temp Accuracy | ±1.0 °C |
| Dielectric Constant Range | 1–80 |
| Dielectric Accuracy | ±2.5 |
| Volumetric Water Content Range | 0–100 %vol |
| VWC Accuracy | ±3 %vol |
| EC� | Resolution: 1.0 mS·m⁻¹ |
| Temp Resolution | 0.1 °C |
| VWC Resolution | 0.1 %vol |
| Probe Dimensions | 68 mm length × 3 mm diameter |
| Housing Dimensions | 55 × 45 × 10 mm |
| Weight | 75 g |
| IP Rating | IP67 (sensor), IP65 (connector) |
| Operating Temp | 0–50 °C |
| Response Time | <5 s |
| Excitation Frequency | 20 MHz |
| Data Storage | 2100 readings (via HH2 meter) |
| Power | 9 V alkaline battery |
Overview
The Delta-T Devices WET-2 is a compact, field-deployable multi-parameter soil sensor engineered for simultaneous, in-situ measurement of volumetric water content (VWC), bulk electrical conductivity (ECb), and soil temperature. Based on Frequency Domain Reflectometry (FDR) at 20 MHz, the WET-2 employs a calibrated three-electrode probe geometry to deliver rapid, repeatable measurements without requiring soil-specific calibration for standard mineral soils. Its robust stainless-steel probe and IP67-rated housing ensure reliable operation under variable field conditions—including saturated, frozen, or saline environments—making it suitable for long-term deployment in agronomic trials, ecological monitoring, horticultural research, and soil hydrological modeling.
Key Features
- Integrated triple-parameter sensing: simultaneous acquisition of VWC, ECb, and temperature within a single 68 mm probe
- FDR-based dielectric measurement with factory calibration traceable to NIST-standard reference soils
- High-speed response (<5 s per reading) and low power consumption enabling extended battery life on 9 V alkaline cells
- IP67-rated probe body and IP65-rated connector interface for resistance to dust ingress and temporary submersion
- Modular compatibility with Delta-T’s HH2 handheld meter (2100-point internal memory) and GP1/GP2 data loggers for autonomous, time-series monitoring
- Optional base calibration upgrade available for non-standard media—including peat, compost, wool, coal ash, and fibrous substrates—supporting method validation per ISO 11277 and ASTM D5534
Sample Compatibility & Compliance
The WET-2 is validated for use in mineral soils with particle size distributions conforming to USDA textural classes (sand to clay loam). Its FDR algorithm compensates for moderate salinity effects on permittivity, enabling stable VWC estimation across ECb ranges up to 300 mS·m⁻¹ (extendable to 600 mS·m⁻¹ with user-defined calibration). The sensor meets IEC 60529 for ingress protection and complies with electromagnetic compatibility (EMC) requirements per EN 61326-1 for laboratory and field instrumentation. When deployed with GP2 loggers and configured for audit-trail-enabled data capture, the system supports GLP-compliant workflows including timestamped metadata logging, operator ID tagging, and change history retention—facilitating alignment with ISO/IEC 17025 and FDA 21 CFR Part 11 data integrity expectations for regulated environmental studies.
Software & Data Management
Data collected via HH2 or GP-series loggers is exported in CSV format through Delta-T’s free PC software (WET-2 Utility v4.x), supporting batch processing, unit conversion (e.g., ECb to ECp using Rhoades model), and VWC correction for temperature-induced dielectric drift. The software includes built-in uncertainty propagation tools aligned with GUM (JCGM 100:2008) methodology. For networked deployments, GP2 units support SDI-12 output and Modbus RTU over RS-485, enabling integration into SCADA systems or cloud platforms (e.g., ThingSpeak, AWS IoT Core) via third-party gateways. All firmware updates and calibration certificates are digitally signed and version-controlled to maintain traceability throughout instrument lifecycle.
Applications
- Irrigation scheduling and deficit irrigation trials in precision viticulture and protected horticulture
- Salinity mapping and leaching requirement assessment in reclaimed coastal or arid-zone soils
- Root-zone monitoring in containerized nursery stock and vertical farming substrates
- Soil moisture–temperature–conductivity coupling analysis for biogeochemical process modeling (e.g., nitrification, denitrification)
- Validation of remote sensing soil moisture products (e.g., Sentinel-1 SAR, SMAP L-band) at field scale
- Long-term edaphic monitoring in LTER (Long Term Ecological Research) networks and UNESCO biosphere reserves
FAQ
Can the WET-2 be used in organic or high-OM soils?
Yes—when paired with the optional base calibration upgrade, the sensor supports empirical recalibration for organic media such as peat, coir, and compost, with documented accuracy maintained per ISO 14246 protocols.
Is temperature compensation applied automatically during VWC calculation?
Yes—the embedded firmware applies real-time temperature correction to dielectric readings using a polynomial fit derived from controlled lab validation across −5 to +50 °C.
What is the recommended insertion depth and spacing for representative sampling?
The 68 mm probe is optimized for topsoil (0–10 cm) characterization; for profile analysis, multiple probes should be installed at staggered depths with ≥10 cm horizontal separation to avoid electromagnetic interference.
Does the WET-2 require routine recalibration in the field?
No—factory calibration remains stable for ≥2 years under normal use; annual verification against gravimetric samples is recommended for critical applications per ISO 11465.
Can ECb data be converted to pore water conductivity (ECp)?
Yes—Delta-T’s software implements the Rhoades, van Genuchten, and Hilhorst models for ECb–ECp transformation, with user-selectable texture inputs to constrain parameterization.
