|  |

| |

Enabling better global research outcomes in soil, plant & environmental monitoring.

HFD8-100 Heat Field Deformation

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

  • Standalone system with integrated logger and battery

HFD8 Model Differences (HFD8-50 and HFD8-100)

The HFD8-50 differs from the HFD8-100 only in the length of the probe needles. HFD8-100 Measurement needles feature a 10mm spacing between sensors while the HFD8-50 Measurement probes feature a 5mm measurement point spacing, offering an improved sap flow resolution. The shorter needles of the HFD8-50 also significantly reduce the time required for installation.


  • Stand-alone logging
  • MicroSD expandable memory
  • 8GB MicroSD Removable Storage Card (capacity: 10+ years data storage)
  • Wireless connectivity and data transfer
  • Simple conversion and scripting
  • Flexible sensor calibration, look-up tables, and user scripts
  • 24-Bit resolution
  • IP65 rated water proof enclosure
  • Free Windows and Mac utility configuration software
  • Optional wireless logging

Power management:

  • Field: direct connected solar panel
  • Lab: mains DC power supply
  • Internal Lithium-Polymer battery
  • Internal Lithium-Polymer battery charger and power management

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.

One Week of Sap Flow Data, HFD – Almond Tree

a. Sap flux rates were observed to be highest in the outer sapwood area, near the cambium, and lowest towards the heartwood.
Sap Flux Density

b. Rainfall event on day three and cloud cover on day four represented by a reduction in sap flux rates, and total sapflow volumes.
Sap Flux Density 2d

c. Cumulative sap flow for one week was calculated to be 33.63L.
Sap Flow Rate

Principle of measurement

The HFD technique is a thermodynamic method based on measuring the dT 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 (dTsym) allows bi-directional (acropetal and basipetal) and very low flow measurements, whereas asymmetrical temperature difference (dTas) 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 dTs-a or dTas for a zero flow condition. Under flow conditions the parameter K can be extrapolated with accuracy using linear regression.The-ICT-International-Journey 150520

Instrument Logging

Resolution 0.00001V—24-Bit
Accuracy 0.001V
Minimum Logging Interval 1 second
Delayed Start Suspend Logging, Customised Intervals
Sampling Frequency 10Hz


Communications USB, Wireless Radio Frequency 2.4 GHz
Data Storage MicroSD Card, SD, SDHC & SDXC Compatible (FAT32 format)
Software Compatibility Windows 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, 8GB microSD card included.

Operating Conditions

Temperature Range -40°C to +80°C
R/H Range 0-100%
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
  • With a recommended power source connected, operation can be continuous.
  • CH24 - 24 Volt Power Supply
    The CH24 is a 100 - 240Volts AC Mains to 24Volts DC power supply adapter; capable of outputting up to 2.5Amps. For most ICT Instruments.
  • HFD Drill Bits 1.9 mm
    HFD Drill Bits 1.9 mm O.D x 150 mm long.
  • HFD Drill Bits 2.0 mm
    HFD Drill Bits 2.0 mm O.D x 150 mm long.
  • DR Dremel 800 Chuck Collet
    This DR Dremel 800 Collet is necessary in order that the small diameter drill bits, as used for the installation of the SFM1 needles, can be inserted into the SFM-DR Dremel Drill Chuck.
  • HFD Installation Kit
    Heat Field Deformation Sensor Installation Kit Includes: 5 x 1.9 mm and 5 x 2.0 mm Drill bits, 2 x locating Sleeves, 1 x SFM-IT insertion tool, inert grease in syringe to aid installation & thermal coupling of needle & sleeve to xylem installation video on DVD.
    Set of HFD needles. 3 x Temperature and 1 x Heater Needle.
    HFD sleeve set for one HFD8 logger installation (inclusive 4 pieces) Consists of 3 x 100mm long closed-end sleeves for measurement needles and 1 x 120mm long closed-end sleeve for the heater.
  • ICT Universal Telemetry Hub
    ICT Universal Telemetry Hub
  • MCC Mini
    The MCC Mini is a simple to use USB Serial to Radio Communications device providing a high level of integrity in data transfers. Its miniature design and minimalist approach make it an attractive solution for portable computers and less intrusive workstation setups where space and weight are of concern.
  • Data to the Web
    Wireless Communication Module - Includes; MCC Radio Frequency Logging Hub, Comms and ICT Data View Software, GSM/2G/3G modem, 3V 5Ah Lithium Polymer Battery, 11W solar panel, IP66 enclosure. 
  • Wireless Data Collector
    Wireless data logger. 4GB SD Card storage. Communicates with any ICT International instrument.
  • SFT1 Sap Flow Tool
    Sap Flow Tool software for HFD and HRM. Single License. Unlimited access to any number HRM or HFD datasets. Configured to analyse HRMx, CHPM, Tmax data from the SFM Sap Flow Meter. Visualise PSY1, soil moisture, and meteorological data.
  • SP22 - 20 Watt Solar Panel
    SP22 - 20 Watt Solar Panel with 4m cable suitable for powering our SFM1, PSY1, HFD, SOM1, SMM1 etc products.

David, T. S., David, J. S., Pinto, C. A., Cermak, J., Nadezhdin, V., & Nadezhdina, N. (2012). Hydraulic connectivity from roots to branches depicted through sap flow: Analysis on a Quercus suber tree. Functional Plant Biology, 39(2), 103–115. https://doi.org/10.1071/FP11185

Eliades, M., Bruggeman, A., Djuma, H., and Lubczynski, M. W. (2018). Tree Water Dynamics in a Semi-Arid, Pinus brutia Forest. Water, 10(8), 1039. https://doi.org/10.3390/w10081039

Eliades, M., Bruggeman, A., Lubczynski, M. W., Christou, A., Camera, C., Djuma, H. (2017). The water balance components of Mediterranean pine trees on a steep mountain slope during two hydrologically contrasting years. Journal of Hydrology, 562, 712–724. https://doi.org/10.1016/j.jhydrol.2018.05.048

Guyot, A., Ostergaard, K. T., Fan, J., Santini, N. S., & Lockington, D. A. (2015). Xylem hydraulic properties in subtropical coniferous trees influence radial patterns of sap flow: Implications for whole tree transpiration estimates using sap flow sensors. Trees, 29(4), 961–972. https://doi.org/10.1007/s00468-014-1144-5

Nadezhdina, N., Vandegehuchte, M. W., & Steppe, K. (2012). Sap flux density measurements based on the heat field deformation method. Trees, 26(5), 1439–1448. https://doi.org/10.1007/s00468-012-0718-3

Van de Wal, B. A., Guyot, A., Lovelock, C. E., Lockington, D. A., & Steppe, K. (2015). Influence of temporospatial variation in sap flux density on estimates of whole-tree water use in Avicennia marina. Trees, 29(1), 215–222. https://doi.org/10.1007/s00468-014-1105-z

Link, R. M., Fuchs, S., Arias Aguilar, D., Leuschner, C., Castillo Ugalde, M., Valverde Otarola, J. C., & Schuldt, B. (2020). Tree height predicts the shape of radial sap flow profiles of Costa-Rican tropical dry forest tree species. Agricultural and Forest Meteorology, 287, 107913. https://doi.org/10.1016/j.agrformet.2020.107913