For the measurement of sap flow or transpiration in plants.
The Heat Field Deformation (HFD) technique is ideally suited to sap flow research projects that require the measurement of extended radial sap flow profiles to accurately map hydraulic architecture of trees. Similar to the HRM sap flow sensor the HFD sensor can measure high sap flow rates as well as low to zero and reverse sap flow.
Heat Field Deformation – Sap Flow Meter Features
|Minimum Logging Interval||1 second|
|Delayed Start||Suspend Logging, Customised Intervals|
|Communications||USB, Wireless Radio Frequency 2.4 GHz|
|Data Storage||MicroSD Card, SD, SDHC & SDXC Compatible (FAT32 format)|
|Software Compatibility||Windows 7, 8, 8.1, 10 and Mac|
|Data Compatibility||FAT32 compatible for direct exchange of SD card with any Windows PC or Mac|
|Data File Format||Comma Separated Values (CSV) for compatibility with all software programs|
|Memory Capacity||Up to 16GB, 4GB microSD card included.|
|Temperature Range||-40°C to +80°C|
|Dual Firmware||User Upgradeable firmware using USB boot strap loader function|
|Length x Width x Depth||340 x 84 x 35 mm|
|Weight||915g (Including mounting brackets)|
|Internal Battery Specifications|
|4.8Ah Lithium Polymer, 4.20 Volts fully charged|
|External Power Requirements|
|Bus Power||8-30 Volts DC, non-polarised, current draw is 340mA maximum at 17 volts per logger|
|USB Power||5 Volts DC|
|Internal Charge Rate|
|Bus Power||60mA – 700mA Variable internal charge rate, maximum charge rate of 700mA active when the external voltage rises above 16 Volts DC|
|USB Power||100mA fixed charge rate|
|Internal Power Management|
|Fully Charged Battery||4.20 Volts|
|Low Power Mode||3.60 Volts – Instrument ceases to take measurements|
|Discharged Battery||2.90 Volts – Instrument automatically switches off at and below this voltage when no external power connected.|
|Battery Life varies|
The Heat Field Deformation (HFD) technique is a radically new method for measuring sap flow. It is ideally suited to sap flow research projects that require the measurement of extended radial sap flow profiles to accurately map hydraulic architecture of trees. Similar to the HRM sap flow sensor the HFD sensor can measure high sap flow rates as well as low to zero and reverse sap flow. Hence as both sensors can measure in the same range the HFD sensor provides an extension of the HRM method making both sensors highly complimentary to each other in most sap flow measurement applications.
Developed by Dr. Nadezda Nadezhdina, (Mendel University, Czech Republic) the HFD technique has been used in published sap flow research since 1998 to study many previously unanswered plant physiological questions.
Nadezhdina N., Ferreira M. I., Silva R., Pacheco C.A. (2008) Seasonal variation of water uptake of a Quercus suber tree in Central Portugal. Plant and Soil, 305: 105-119.
The HFD technique is a thermodynamic method based on measuring the ΔT of the sapwood both symmetrically (in the axial direction, above and below) and asymmetrically (in the tangential direction or to the side) around a line heater.
The heater is continuously heated at approx 50 mA and generates an elliptical heat field under zero flow conditions. Sap flow significantly deforms the heat field by elongating the ellipse as shown in the photo of a thermal image of a HFD measurement. The symmetrical temperature difference (ΔTsym) allows bi-directional (acropetal and basipetal) and very low flow measurements, whereas asymmetrical temperature difference (ΔTas) is primarily responsible for the magnitude of medium and high sap flow rates.
By using the ratio of measured temperature differences and applying correction for each measurement points local conditions using the adjustable K-values the common features of the medium (such as variable water content, natural temperature gradients and, wound effects) have negligible impact on sap flow calculations.
The value for parameter K is equal to the absolute value of ΔTs-a or ΔTas for a zero flow condition. Under flow conditions the parameter K can be extrapolated with accuracy using linear regression.