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Tmax Method

The Tmax method employs a temperature needle downstream (below) a line heater needle. The amount of time taken for the maximum rise in temperature following a heat pulse from the heater needle is recorded. According to well defined heat transport equations, derived from Marshall (1958), the heat velocity is calculated.

The SFM1 Sap Flow Meter can be configured to measure sap flow via the Tmax method. Raw temperature data is collected by the SFM1 instrument and later downloaded into the Sap Flow Tool software. In Sap Flow Tool, raw data can be quickly and easily manipulated to give heat velocity and sap flow data via the Tmax equations.


Output Options

Raw Temperatures:°C
Heat Pulse Velocity cm hr-1
Sap Velocity: cm hr-1
Sap Flow: cm3 hr-1(Litres hr-1)


-100 to +100 cm hr-1


0.01 cm hr-1


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


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. 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.

Instrumentation for Total Tree Water Use and “Behaviour”

Instrument design

The HRM probes consists 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 an 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 nonvolatile memory. The HRM Sap Flow Meter displays information such as external battery status, Serial Number, firmware version, SD Card Status, Measurement interval, Data reporting option, & correction factors. The utility software enables the Sap Flow Meter can be used in the 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.

SFM Software


Data Analysis

Data can be manually processed using a spreadsheet such as Excel by opening the comma separated values (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
  • 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.
  • 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.

Ambrose, A R., S. C. Sillett, G. W. Koch, R. v. Pelt, M. E. Antoine and T. E. Dawson (2010) Effects of height on treetop transpiration and stomatal conductance in coast redwood (Sequoia sempervirens). Tree Physiology, 30: 1260-1272.


Bleby, T. M., S. S. O. Burgess and M. A. Adams (2004) A validation, comparison and error analysis of two heat-pulse methods for measuring sap flow in Eucalyptus marginata saplings. Functional Plant Biology, 36: 645-658.


Buckley, T. N., T. L. Turnbull, S. Pfautsch and M. A. Adams (2011) Nocturnal water loss in mature subalpine Eucalyptus delegatensis tall open forests and adjacent E. pauciflora woodlands. Ecology and Evolution, Open Access


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


Buckley, T. N., T. L. Turnbull, S. Pfautsch, M. Gharun and M. A. Adams (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. O., M. A. Adams, N. C. Turner, C. R. Beverly, C. K. Ong, A. A. H. Khan and T. M. Bleby (2001) An improved heat pulse method to measure low and reverse rates of sap flow in woody plants. Tree Physiology, 21: 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) Correction: An improved heat pulse method to measure low and reverse rates of sap flow in woody plants. Tree Physiology, 21: 1157.


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


Doronila, A. I. and M. A. Forster (2013) Performance measurement via sap flow monitoring of three Eucalyptus species for mine site and dryland salinity phytoremediation. International Journal of Phytoremediation.


Drake, P. L., Coleman, B.F., and R. Vogwill (2012) The response of semi-arid ephemeral wetland plants to flooding: linking water use to hydrological processes. Ecohydrology, 6: 852-862.


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


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


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


Mitchell, P.J., E. Veneklaas, H. Lambers and S. Burgess (2009) Partitioning of evapotranspiration in a semi-arid eucalypt woodland in south-western Australia. Agricultural and Forest Meteorology, 140: 25-37.


Palmer, A. R., S. Fuentes, D. Taylor, C. Macinnis-Ng, M. Zeppel, I. Yunusa and D. Eamus (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: 1-10.


Pfautsch, S., C. Keitel, T. L. Turnbull, M. J. Braimbridge, T. E. Wright, R. R. Simpson, J. A. O’Brien and M. A. Adams (2011) Diurnal patterns of water use in Eucalyptus victrix indicate pronounced desiccation–rehydration cycles despite unlimited water supply. Tree Physiology, 31: 1041-1051.


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


Resco de Dios V, R. Diaz-Sierra, M. L. Goulden, C. V. M. Barton, M. M. Boer, A. Gessler, J. P. Ferrio, S. Pfautsch and D. T. Tissue (2013) Woody clockworks: circadian regulation of night-time water use in Eucalyptus globulus. New Phytologist, 200: 743-752.


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


Staudt, K., A. Serafimovicha, L. Siebickea, D. Pyles and E. Falgec (2011) Vertical structure of evapotranspiration at a forest site (a case study). Agricultural and Forest Meteorology, 151: 709-729.


Zeppel, M. J. B., J. D. Lewis, B. Medlyn, C. V. M. Barton, R. A. Duursma, D. Eamus, M. A. Adams, N. Phillips, D. S. Ellsworth, M. A. Forster and D. T. Tissue (2011) Interactive effects of elevated CO2 and drought on nocturnal water fluxes in Eucalyptus saligna. Tree Physiology, 31: 932-934.