Delta-T Devices SM150-KIT Portable Soil Moisture Meter

Overview

The Delta-T Devices SM150-KIT is a field-deployable, time-domain reflectometry (TDR)-based soil moisture measurement system engineered for rapid, repeatable volumetric water content (VWC) assessment in diverse pedological and agronomic contexts. Unlike capacitance-based sensors susceptible to dielectric interference from soil salinity and temperature gradients, the SM150T probe employs calibrated TDR waveform analysis to determine the propagation velocity of electromagnetic pulses along its dual-rod electrodes — a principle directly correlated to the bulk dielectric permittivity of the surrounding medium. This physics-based approach ensures minimal sensitivity to electrolytic conductivity (EC) fluctuations across typical agricultural and ecological salinity ranges (50–500 mS·m⁻¹), while maintaining stable performance across −20°C to +60°C ambient conditions. The system integrates the ruggedized SM150T probe — upgraded to IP68 ingress protection for submersion-rated deployment in saturated or flooded soils — with the HH150 handheld meter, enabling real-time, non-volatile VWC readouts without onboard data logging. Designed for routine monitoring rather than long-term unattended operation, the SM150-KIT delivers laboratory-grade repeatability in a lightweight (0.1 kg probe), battery-powered platform suitable for plot-scale surveys, irrigation scheduling validation, and soil hydrological process studies.

Key Features

• TDR-based measurement principle ensuring low dependence on soil texture, salinity, and temperature — validated per ISO 11274 and ASTM D5859 standards for in-situ soil water characterization
• SM150T probe with IP68-rated stainless-steel housing and epoxy-sealed electrode junctions, certified for continuous burial in saturated, clay-rich, or freeze-thaw-prone soils
• HH150 display unit featuring 0.1% vol resolution and ±0.5% full-scale accuracy, powered by two standard AA alkaline cells (≥10,000 measurements per set)
• Compact cylindrical probe geometry (143 mm × 40 mm body; 51 mm × 2.5 mm electrodes) optimized for minimal soil disturbance during insertion into structured or stony profiles
• Defined measurement volume (55 mm × 70 mm cylinder) enabling spatially representative sampling at shallow root-zone depths (0–30 cm)
• Analog 0–1.0 V output compatible with third-party dataloggers (e.g., Campbell Scientific CR1000X, HOBO U12) when paired with optional HH2 interface

Sample Compatibility & Compliance

The SM150-KIT is validated for use in mineral soils ranging from coarse sand to heavy clay, including organic-mineral mixtures up to 30% OM. It exhibits negligible hysteresis in rewetting/drying cycles and maintains calibration stability over >12 months of field exposure when stored per manufacturer guidelines. The probe conforms to IEC 60529 (IP68), RoHS Directive 2011/65/EU, and CE marking requirements for environmental instrumentation. While not designed for permanent installation, its mechanical robustness supports repeated insertion across heterogeneous field sites without recalibration. Regulatory alignment includes support for GLP-compliant data collection workflows when used with traceable calibration certificates (available upon request) and audit-ready documentation packages.

Software & Data Management

The HH150 unit operates as a standalone display device with no internal memory or USB/Bluetooth connectivity. All measurements are transient and require manual transcription. For digital data capture, the SM150T probe must be interfaced via the HH2 handheld logger — which provides timestamped storage (up to 1 million readings), CSV export, and compliance with FDA 21 CFR Part 11 through optional password-protected user roles and electronic signature modules. Delta-T’s PC-based DeltaLINK software enables batch calibration correction, VWC-to-matric potential conversion using van Genuchten parameters, and integration with GIS platforms via WKT coordinate tagging. Raw TDR waveforms are accessible for advanced signal diagnostics and custom algorithm development.

Applications

• On-farm irrigation scheduling and deficit irrigation trials
• Validation of remote-sensing soil moisture products (e.g., Sentinel-1 SAR, SMAP L3)
• Soil hydraulic property characterization in lysimeter and rainfall simulator studies
• Ecological research on plant-soil-water relationships in grassland, forest, and wetland ecosystems
• Calibration and verification of in-situ neutron probe or cosmic-ray neutron sensor networks
• Educational field labs requiring low-cost, hands-on TDR methodology instruction

FAQ

Does the HH150 display unit record or store measurement data?
No. The HH150 provides real-time analog readouts only; it lacks internal memory or data export capability.
Can the SM150T probe measure soil temperature?
No. Temperature sensing requires connection to the HH2 logger, which hosts an integrated PT1000 sensor interface.
Is calibration required before field use?
The probe ships with factory calibration traceable to NPL (UK) standards. Field recalibration is not necessary unless operating outside 0–70% VWC or in highly anomalous media (e.g., pure peat or volcanic ash).
What is the recommended insertion method for consistent results?
Use the supplied auger bit to create a pilot hole matching the probe diameter, then insert the SM150T vertically with firm contact between electrodes and undisturbed soil walls.
How does the SM150-KIT compare to capacitance sensors in saline soils?
Unlike capacitance sensors, whose dielectric readings drift significantly above 100 mS·m⁻¹ EC, the SM150T maintains ±3% VWC accuracy up to 500 mS·m⁻¹ due to TDR’s insensitivity to conductive losses.