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SFM1 Sap Flow Meter

The SFM1 Sap Flow Meter is a self contained, stand-alone instrument for the measurement of sap flow or transpiration in plants. The SFM1 is a complete package containing sap flow sensors, data logger, interface software and internal battery which can be charged with an external solar panel. The SFM1 Sap Flow Meter is a new model which replaces the HRM30 sap flow measurement sensor.

Utilising the Heat Ratio Method (HRM) principle the SFM1 Sap Flow Meter is able to measure high, low and reverse flow rates in both small woody stems & roots as well as large trees. Like the Heat Field Deformation (HFD) principle, the HRM Sap Flow Meter is the only instrument that can measure zero flow and reverse sap flow rates. The SFM1 Sap Flow Meter is the most powerful and flexible instrument for the direct measurement of plant water use.


  • Low & Zero Sap Flow Rates
  • Reverse Sap Flow Rates
  • Night Time Water Loss
  • Stem Sizes>10mm
  • Sap Flow in Roots
  • Arid Ecosystems & Drought
  • Radial Sap Velocity Profiles
  • Sap Flow of Grapevines

 Accessories include:

– SFT1 – Sap Flow Tool Software
– MCC1 – Wireless USB Radio communication device
– MCC2G – Remote Data Access Hub for Data To Web access via GSM
– SFM-SK1 – SFM Installation Kit
– SFM-55 – Pack of 10 Drill Bits
– SFM-TB – HRM block, Functional verification standard
– SP22 – 20 Watt Solar Panel and SPPM – Solar Panel Post Mount


Output Options Raw Temperatures: °C
Heat Pulse Velocity: cm hr-1
Sap Velocity: cm hr-1
Sap Flow: cm3 hr-1 (Litres hr-1)
Range -100 to +100 cm hr-1
Resolution 0.01 cm hr-1
Accuracy 0.5 cm hr-1
Measurement Duration 120 seconds


Computer Interface USB, Wireless RF 2.4 GHz
Data Storage MicroSD Card
Memory Capacity Up to 16GB, 4GB MicroSD card included.


Heat Pulse User Adjustable: 20 Joules (default) approx. Equivalent to a 2.5 second heat pulse duration, auto scaling.
User Adjustable: Minimum interval, 3 minutes, recommended minimum 10 minutes.


Needle Diameter 1.3 mm
Needle Length 35 mm
Measurement Positions 2 per measurement needle
Measurement Spacings 7.5 mm and 22.5 mm from the needle tip
Dimensions L x W X D 170 x 80 x 35 mm
Weight 400 g


Internal Battery Specifications
960mAh Lithium Polymer, 4.20 Volts fully charged
External Power Requirements
Bus Power 8-30 Volts DC, non-polarised, current draw is 190mA maximum at 17 volts per logger
USB Power 5 Volts DC
Internal Charge Rate
Bus Power 60mA – 200mA Variable internal charge rate, maximum charge rate of 200mA 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.
  • Approximately 1.5 days with a heat pulse of 50 Joules and a measurement interval of 30 minutes – no external power present to recharge battery.

The Heat Ratio Method

Developed by the University of Western Australia and partner organisations, ICRAF and CSIRO, the HRM principle has been validated against gravimetric measurements of transpiration and used in published sap flow research since 1998. Burgess, S.S.O., 2001 An improved heat pulse method to measure low and reverse rates of sap flow in woody plants Tree Physiology 21, 589-598. Heat Ratio Method (HRM) is an improvement of the Compensation Heat Pulse Method (CHPM). Being a modified heat pulse technique power consumption is very low using approx 70 mAmp per day at a 10 minute temporal sampling interval under average transpiration rates. The HRM needles have two radial measurement points for the characterisation of radial sap flow gradients making measurements more accurate.

 Installed SFM1
Through microprocessor control, the inner measurement point can be activated or deactivated dependent on the specific wood anatomy of the species being measured. This provides a great flexibility in stem diameter range from >10 mm diameter woody stems or roots to the world’s largest trees, thus enabling water flows to be monitored in stems and roots of a wide range of different species, sizes and environmental conditions including drought or water stress.

Instrument design

The SFM1 probes consist of three 35mm long needles integrally connected to a 16-bit microprocessor. The top and bottom probes contain two sets of matched and calibrated high precision thermistors located at 7.5mm and 22.5mm from the tip of each probe. The third and centrally located needle is a line heater that runs the full length of the needle to deliver a uniform and exact pulse of heat through the sapwood.

Instrument Configuration & operation

All aspects of the instruments operation and calculations are controlled by the microprocessor which automatically converts the analogue microvolt signals to a calibrated output. Programming variables such as heat pulse interval, energy input, probe spacings, and measurement frequency are all held resident in non-volatile memory. The HRM Sap Flow Meter displays information such as external battery status, Serial Number, firmware version, SD Card Status, Measurement interval, Data reporting options and correction factors. The utility software enables the Sap Flow Meter to be used in manual mode. This provides the ability to evaluate the efficacy of pulse intervals by viewing the raw measured temperatures on screen. Subsequent reports can then be viewed detailing the the duration of time the heat pulse required to deliver the exact amount of heat energy in Joules, the temperature rise following the previous heat pulse, temperature ratios between measurement points, sap velocity or sap flow.
Combined Instrument Software Interface - Sap Flow

Data Analysis

Data can be manually processed using a spreadsheet program such as Excel to open the comma separated value (CSV) file provided by the Sap Flow Meter. More powerful and immediate processing can be achieved by directly importing the data file into the Sap Flow Tool Software. Thus providing instant 2 dimensional and 3D graphing of the raw heat pulse velocity and processing of sap velocity and sap flux. The entire data set can be instantly reprocessed if correction factors require modification or additional information becomes available.
Sap Flow Software


  • 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.
  • ICT CIS - Cloud Data Analysis and Display
    The ICT CIS and DataView.
  • 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 Communication
    Wireless USB Radio communication device.
  • Wireless Data Collector
    Wireless data logger. 4GB SD Card storage. Communicates with any ICT International instrument. Includes SPBP07 power supply.
  • SFM-SK1 Installation kit
    SFM-SK1 Installation kit
  • SFM-DR Dremel 8000
    Dremel 8000 for SFM1 installation
  • 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.
  • The HRM Test Block
    The HRM Sap Flow Meter Test Block is a functional verification standard for use with the HRM Sap Flow Meter.

The following papers either cite the SFM1 Sap Flow Meter or HRM30 Sensor on the SL-5 Smart Logger:

Ambrose, A. R., Sillett, S. C., Koch, G. W., Van Pelt, R., Antoine, M. E., & Dawson, T. E. (2010). Effects of height on treetop transpiration and stomatal conductance in coast redwood (Sequoia sempervirens). Tree Physiology. doi:10.1093/treephys/tpq064

Bleby, T. M., Burgess, S. S., & Adams, M. A. (2004). A validation, comparison and error analysis of two heat-pulse methods for measuring sap flow in Eucalyptus marginata saplings. Functional Plant Biology, 31(6), 645-658.

Buckley, T. N., Turnbull, T. L., Pfautsch, S., & Adams, M. A. (2011). Nocturnal water loss in mature subalpine Eucalyptus delegatensis tall open forests and adjacent E. pauciflora woodlands. Ecology and evolution, 1(3), 435-450.

Buckley, T. N., Turnbull, T. L., & Adams, M. A. (2012). Simple models for stomatal conductance derived from a process model: cross‐validation against sap flux data. Plant, cell & environment, 35(9), 1647-1662.

Buckley, T. N., Turnbull, T. L., Pfautsch, S., Gharun, M., & Adams, M. A. (2012). Differences in water use between mature and post-fire regrowth stands of subalpine Eucalyptus delegatensis R. Baker. Forest Ecology and Management, 270, 1-10.

Burgess, S. S., Adams, M. A., Turner, N. C., Beverly, C. R., Ong, C. K., Khan, A. A., & Bleby, T. M. (2001). An improved heat pulse method to measure low and reverse rates of sap flow in woody plants. Tree Physiology, 21(9), 589-598.

Burgess, S. S. O., M. A. Adams, N. C. Turner, C. K. Ong, A. A. H. Khan, C. R. Beverly and T. M. Bleby (2001) Corrections: An improved heat pulse method to measure low and reverse rates of sap flow in woody plants. Tree Physiology, 21(16), 1157. doi:10.1093/treephys/21.16.1157

Carbone, M. S., Park Williams, A., Ambrose, A. R., Boot, C. M., Bradley, E. S., Dawson, T. E., … & Still, C. J. (2013). Cloud shading and fog drip influence the metabolism of a coastal pine ecosystem. Global Change Biology, 19(2), 484-497.

De Groote, S. (2013). Impact of dew and rain on the water relations of the mangrove species Avicennia marina (Forssk.) Vierh (Doctoral dissertation, Master’s thesis, University Ghent, Faculty of Bioscience Engineering). Click to view Paper

Doronila, A. I., & Forster, M. A. (2015). Performance measurement via sap flow monitoring of three Eucalyptus species for mine site and dryland salinity phytoremediation. International journal of phytoremediation, 17(2), 101-108.

Downey A., Winter, W., Cull, P. (2013). Smart trees, smart kids – empowering a generation through the science of sap flow. ICT International. Downey et al Smart Trees Smart Kids – Empowering a Generation through the Science of Sap Flow

Drake, P. L., Coleman, B. F., & Vogwill, R. (2013). The response of semi‐arid ephemeral wetland plants to flooding: linking water use to hydrological processes. Ecohydrology, 6(5), 852-862.

Eller, C. B., Lima, A. L., & Oliveira, R. S. (2013). Foliar uptake of fog water and transport belowground alleviates drought effects in the cloud forest tree species, Drimys brasiliensis (Winteraceae). New Phytologist, 199(1), 151-162.

Falge, E., & Meixner, F. X. (2008). Validation of a 3D gas exchange model for a Picea abies canopy in the Fichtelgebirge, Germany. In Geophys. Res. Abstr (Vol. 10). Download PDF.

Forster, M. A. (2012). Quantifying water use in a plant–fungal interaction. Fungal Ecology, 5(6), 702-709.

Gharun, M., Turnbull, T. L., & Adams, M. A. (2013). Stand water use status in relation to fire in a mixed species eucalypt forest. Forest Ecology and Management, 304, 162-170.

Gharun, M., Turnbull, T. L., Pfautsch, S., & Adams, M. A. (2015). Stomatal structure and physiology do not explain differences in water use among montane eucalypts. Oecologia, 177(4), 1171-1181.

Mitchell, P. J., Veneklaas, E., Lambers, H., & Burgess, S. S. (2009). Partitioning of evapotranspiration in a semi-arid eucalypt woodland in south-western Australia. Agricultural and Forest Meteorology, 149(1), 25-37.

Palmer, A. R., Fuentes, S., Taylor, D., Macinnis‐Ng, C., Zeppel, M., Yunusa, I., & Eamus, D. (2010). Towards a spatial understanding of water use of several land‐cover classes: an examination of relationships amongst pre‐dawn leaf water potential, vegetation water use, aridity and MODIS LAI. Ecohydrology, 3(1), 1-10.

Patankar, R., Quinton, W. L., Hayashi, M., & Baltzer, J. L. (2015). Sap flow responses to seasonal thaw and permafrost degradation in a subarctic boreal peatland. Trees, 29(1), 129-142.

Pfautsch, S., Dodson, W., Madden, S., & Adams, M. A. (2015). Assessing the impact of large‐scale water table modifications on riparian trees: a case study from Australia. Ecohydrology, 8(4), 642-651.  PDF

Pfautsch, S., Keitel, C., Turnbull, T. L., Braimbridge, M. J., Wright, T. E., Simpson, R. R., … & Adams, M. A. (2011). Diurnal patterns of water use in Eucalyptus victrix indicate pronounced desiccation–rehydration cycles despite unlimited water supply. Tree physiology, 31, 1041-1051. doi:10.1093/treephys/tpr082

Pfautsch, S., Peri, P. L., Macfarlane, C., van Ogtrop, F., & Adams, M. A. (2014). Relating water use to morphology and environment of Nothofagus from the world’s most southern forests. Trees, 28(1), 125-136.

Resco de Dios, V., Díaz‐Sierra, R., Goulden, M. L., Barton, C. V., Boer, M. M., Gessler, A., … & Tissue, D. T. (2013). Woody clockworks: circadian regulation of night‐time water use in Eucalyptus globulus. New Phytologist, 200(3), 743-752.

Rosado, B. H., Oliveira, R. S., Joly, C. A., Aidar, M. P., & Burgess, S. S. (2012). Diversity in nighttime transpiration behavior of woody species of the Atlantic Rain Forest, Brazil. Agricultural and forest meteorology, 158, 13-20.

Staudt, K., Serafimovich, A., Siebicke, L., Pyles, R. D., & Falge, E. (2011). Vertical structure of evapotranspiration at a forest site (a case study). Agricultural and forest meteorology, 151(6), 709-729.

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.

Yang, L., Miki, N. H., Matsuo, N., Zhang, G., Wang, L., & Yoshikawa, K. (2014). Contribution of adventitious roots to water use strategy of Juniperus sabina in a semiarid area of China. Journal of Agricultural Science and Technology. A, 4(3A), 251-259.

Zeppel, M. J., Lewis, J. D., Medlyn, B., Barton, C. V., Duursma, R. A., Eamus, D., … & Tissue, D. T. (2011). Interactive effects of elevated CO2 and drought on nocturnal water fluxes in Eucalyptus saligna. Tree physiology, 31(9), 932-944.