Dynamax EXO-Skin™ Wrap-Around Stem Flow Sensor
| Brand | Dynamax |
|---|---|
| Origin | USA |
| Model | EXO-Skin™ |
| Sensor Type | Heat-Balance-Based Wrap-Around Sap Flow Sensor |
| Diameter Range | 9.5–25 mm |
| Height | 70–120 mm |
| Input Voltage | 4.5 V DC |
| Typical Power Consumption | 0.13–0.48 W |
| Thermocouple Pairs | 2 per unit |
| Enclosure | PTFE-Composite Vapor-Permeable Waterproof Membrane |
| Mounting | Velstretch® Elastic Nylon Band (Breathable, Hydrophobic, Growth-Accommodating) |
Overview
The Dynamax EXO-Skin™ Wrap-Around Stem Flow Sensor is an engineered evolution of the established heat-balance principle for continuous, non-invasive sap flow measurement in woody and semi-woody plant stems. Unlike thermal dissipation (TDP) or heat pulse methods, the EXO-Skin operates on a steady-state axial heat balance model—where a controlled, low-power heater introduces a known thermal input into the stem cross-section, and dual thermocouple pairs measure the resulting temperature gradient upstream and downstream of the heating zone. This gradient, under calibrated conditions, correlates directly with volumetric sap flux density (g·cm−2·s−1). Designed specifically for long-term field deployment in orchards, vineyards, agroforestry systems, and ecological monitoring networks, the EXO-Skin eliminates the need for invasive probe insertion or frequent recalibration—making it suitable for GLP-aligned phenotyping trials and USDA-ARS–supported water-use efficiency studies.
Key Features
- Wrap-around architecture: Single-piece, flexible sensor body conforms to irregular stem geometries without mechanical stress or girdling risk—validated for stems ranging from 9.5 mm to 25 mm in diameter.
- Velstretch® mounting system: Breathable, porous elastic nylon band provides secure adhesion while accommodating radial growth; eliminates re-tensioning or sensor replacement during seasonal expansion.
- Vapor-permeable waterproof membrane: PTFE-based composite outer sheath allows H2O vapor transmission (≥1500 g·m−2·day−1) while blocking liquid water ingress—even under sustained rainfall or high-humidity canopy conditions.
- Modular electronics integration: Separated heater and sensing elements reduce thermal crosstalk and improve signal-to-noise ratio; thermocouple junctions are laser-welded for long-term stability (>5 years in situ).
- Low-power operation: Optimized for solar-powered data loggers (e.g., Campbell Scientific CR1000X, Onset HOBO RX3000); typical draw ranges from 0.13 W (SGEX-9) to 0.48 W (SGEX-25), enabling multi-year deployments with 12 Ah battery packs.
Sample Compatibility & Compliance
The EXO-Skin is validated for use on deciduous and evergreen species including Vitis vinifera, Prunus persica, Malus domestica, Eucalyptus globulus, and Pinus taeda. Its non-invasive design complies with ISO 17025–accredited calibration protocols for plant physiological instrumentation and supports audit-ready data collection under FDA 21 CFR Part 11–enabled logging platforms when paired with Agrisensors Cloud. The sensor’s material composition meets RoHS Directive 2011/65/EU requirements, and its encapsulation system conforms to IEC 60529 IP67 specifications for dust and temporary immersion resistance.
Software & Data Management
Raw thermocouple voltage (µV) and heater voltage/current outputs are compatible with standard analog-input data loggers. Calibration coefficients and real-time sap flux calculations are implemented via the open-source SapFlowPy Python library (v3.2+), which incorporates species-specific allometric corrections and temperature-compensated thermal conductivity models. When deployed with the Agrisensors Cloud Platform, EXO-Skin data undergoes automated QA/QC filtering—including outlier detection based on diurnal pattern deviation, thermal equilibrium validation, and moisture-induced signal drift correction. Audit trails, user access logs, and electronic signatures satisfy GLP/GMP documentation requirements for regulatory submissions.
Applications
- High-resolution irrigation scheduling in commercial vineyards and orchards
- Long-term drought response phenotyping across germplasm collections
- Carbon–water coupling analysis in eddy-covariance flux tower footprints
- Validation of land surface models (e.g., CLM5, ORCHIDEE) at plot scale
- Rootstock–scion hydraulic trait screening under controlled deficit irrigation
- Urban tree water use assessment in municipal green infrastructure monitoring
FAQ
How does the EXO-Skin differ from traditional TDP sensors?
The EXO-Skin uses axial heat balance rather than radial thermal dissipation—enabling direct quantification of total cross-sectional sap flow without empirical K-factor derivation.
Can the sensor be reused across growing seasons?
Yes—its vapor-permeable membrane and growth-accommodating mount allow multi-season deployment on perennial species without physical damage or recalibration drift.
Is calibration required before installation?
Factory calibration is provided per model (SGEX-9 through SGEX-25); field verification using zero-flow nighttime baselines is recommended but not mandatory for comparative studies.
What environmental conditions limit measurement accuracy?
Accuracy degrades below −5 °C (risk of ice formation in xylem) and above 45 °C ambient (exceeding thermocouple linear range); dew point differentials >15 °C may require supplemental ventilation.
Does the EXO-Skin support wireless telemetry?
It outputs analog signals only—but integrates natively with LoRaWAN-enabled gateways (e.g., SensoScientific S2-LR) via compatible analog-to-digital transceivers.
