Implexx Sap Flow Sensor.

A Heat Pulse Velocity Sensor for Researchers.



  • A low cost, calibrated, SDI-12 enabled, heat pulse sap flow sensor;
  • A versatile digital solution so you can allocate more funds to sensors and less to data loggers;
  • Increase sample size and replication;
  • Output calibrated sap flow, heat velocity, stem water content, stem temperature, and more;
  • Calibrated and scientifically backed with peer-reviewed publications.


The Implexx Sap Flow Sensor is an advanced but easy to use sap flow sensor designed by scientists for scientists. The Implexx Sap Flow Sensor is a thermometric sensor based on heat pulse family of methods that have been used by researchers since at least 1930's (Huber, 1932). The Implexx Sap Flow Sensor enables researchers to focus on what they do best: research.

The Implexx Sap Flow Sensor a heat pulse probe which is a three needle design: a central heater needle with downstream and upstream temperature needles.

The Implexx Sap Flow Sensor is a versatile solution for measuring sap flow and plant water relations for scientists. Connect the Implexx Sap Flow Sensor to our range data logging solutions or we can assist you in connecting the Implexx Sap Flow Sensor to your existing dataloggers, IoT devices, RTU's, DAQ's and more.




Implexx Sap Flow Sensor Features
  • Easy to install and requires little ongoing maintenance;
  • Outputs a comprehensive range of 33 parameters per measurement;
  • Or simplifies it down to a single output of calibrated sap flow;
  • Output raw temperature data for your own models and equations;
  • SDI-12 protocol so it can be supported by a large range of data loggers.


Versatile Data Logging Solutions

The Implexx Sap Flow Sensor is supported by the SDI-12 protocol which gives it tremendous flexibility to connect to many data logging devices.

Implexx is supported by a world-wide team of dealers who can provide a comprehensive range of data logging solutions. This includes the complete range of Campbell Scientific data loggers and many more brands.

Alternatively, the Implexx Sap Flow Sensor can be integrated into your existing data logging infrastructure. Implexx provides a comprehensive range of guides and manuals to assist you, or you can contact us for further assistance.


Low Power, Less Management

The Implexx Sap Flow Sensor is a heat pulse style sap flow sensor therefore it requires relatively low power. The Implexx engineers have added features to the Implexx Sap Flow Sensor to further improve the power efficiency of our sap flow sensor. The Implexx Sap Flow Sensor is therefore an ideal sensor for measuring sap flow in forests and remote field sites.

In our experience, we've installed the Implexx Sap Flow Sensor at field sites with the following power requirements:

  • A 20W solar panel, with a 12V 9 amp hour battery, supporting 12 x Implexx Sap Flow Sensors plus a modem, 12 x dendrometers, soil moisture and air temperature sensors;
  • A 5W solar panel, with a 12V 7 amp hour battery, supporting 2 x Implexx Sap Flow Sensors;
  • A stand-alone 12V, 9 amp hour battery, with a 30-minute logging interval, supporting 1 x Implexx Sap Flow Sensor for 30 days.


Measure Fast, Slow and Reverse Sap Flow

The Implexx Sap Flow Sensor is the only commercially available heat pulse sensor that can measure the entire observable range of heat velocity and sap flow in plants.

The Implexx Sap Flow Sensor sensor utilizes the Dual Method Approach (DMA) heat pulse method which has a measurement range is between -200 to >1000 cm/hr (heat velocity) or -100 to >2000 cm³/cm²/hr (sap flux density).

The Implexx Sap Flow Sensor wide measurement range compares with the narrow range of the heat ratio method (HRM; -10 to +15 cm/hr), or the inability of the compensation heat pulse method (+5 to >1000 cm/hr) and Tmax (+10 to >1000 cm/hr) to measure at slow velocities (Forster, 2019). The inability of the other heat pulse methods to measure the entire range of sap flow in plants means they are unreliable, inaccurate and can lead to misinterpretation of data. The Implexx Sap Flow Sensor is the only reliable sensor that can measure the entire range of sap flow in plants.


A Calibrated Sap Flow Sensor

Recent reviews of sap flow methods have strongly recommended that sap flow sensors are calibrated for the trees they are measuring (Steppe et al., 2010; Forster, 2017; Flo et al., 2019). Without a species-specific, or site-specific, calibration, the average error in sap flow estimation is 35% (Forster, 2017).

The Implexx Sap Flow Sensor is the only sap flow sensor available that has a built-in calibration. The Implexx Sap Flow Sensor calibration has been supported by scientific studies demonstrating its accuracy across taxonomically diverse range of 15 woody species. The main output from the Implexx Sap Flow Sensor is calibrated sap flow.

But, as any good scientists knows, you should always check a sensor's calibration against your own standard. Therefore, we provided all the raw data required to check measurements and to perform your own calculations.


Multiple Measurement Points

The Implexx Sap Flow Sensor is configured to measure two sapwood radial depths: outer and inner. Multiple measurement points in the sapwood are advantageous because:

  • increases the accuracy of the Implexx Sap Flow Sensor over older technology such as the thermal dissipation or Granier probe;
  • the outer and inner sapwood provide insights into plant physiological processes; and
  • the ratio of outer to inner sap flow has been used as a measure of water stress.

The outer and inner measurement depths are located at 10 and 20 mm, respectively.


Hydraulic Redistribution and Reverse Flow

The Implexx Sap Flow Sensor is a three-probe configuration with a downstream and upstream temperature needle to a central heater needle. The three-probe configuration means that sap flow can be measured in the positive (i.e. from the roots to the canopy) and reverse (i.e. from the canopy to the roots) direction. This feature cannot be found in single probe or two-needle designs. Therefore, any research on hydraulic redistribution must consider the the Implexx Sap Flow Sensor.

It is also possible to install the Implexx Sap Flow Sensor on the roots. Various configurations of the cable length can be designed to assist and accommodate, as best as possible, these types of research projects. Contact the team at Implexx for more information.


Canopy Stomatal Conductance

The Implexx Sap Flow Sensor, combined with an ATMOS 41 Weather Station, can also be used to measure canopy conductance (also referred to as canopy stomatal conductance).

The Implexx Sap Flow Sensor is installed on the trunk or stem of the plant or tree. Typically, the sensor is installed lower on the trunk beneath the crown. However, some experiments or hypotheses may test canopy conductance at various locations along the trunk such as upper versus lower branches or northern versus southern aspects.

The ATMOS 41 Weather Station is needed to measure atmospheric evaporative demand variables including vapour pressure deficit (VPD), wind, solar radiation, temperature, and relative humidity.

The weather station should be installed as close as possible to the measured plants while still following standard protocols on where to install a weather station (i.e. in the open and away from obstructions).

For detailed information, including equations, methods and statistical analysis, here is an article on how to measure canopy stomatal conductance with the Implexx Sap Flow Sensor.


A Comparison with Other Sap Flow Methods


Feature Specification
Measurement Range -200 to >1000 cm/hr (heat velocity) | -40 to >200 cm3/cm2/hr (sap flux density)
Measurement Accuracy ±0.1 cm/hr
Resolution 0.001 cm/hr
Needle Dimensions 30 mm Length x 1.3 mm Diameter
Position of Thermistors Outer: 10 mm | Inner: 20 mm
Distance Between Needles 6 mm
Epoxy Body Dimensions 40 x 16 mm
Probe Materials 316 marine grade stainless steel
Temperature Range -30 to +70 °C
Thermistor Response Time 200 mSec
Heater Resistance | Output 39 ohms (typical) | 400 J/m (typical)
Power Input 12 VDC
Power Consumption Idle: 4 mA; | Measure: 270 mA | Typical Measurement Cycle: 0.4 mAhr
Sensor Output SDI-12 (ver. 1.4)
Cable Length 5 m (standard) | 60 m (maximum)


The Implexx Sap Flow Sensor Installation Video


Part One: An Introduction to Sap Flow Methods



Part Two: Heat Pulse Velocity Sap Flow Methods



Part Three: The Accuracy of Heat Pulse Methods



Part Four: The Dual Method Approach (DMA)



Part Five: Sap Flow Data Analysis



Manuals & Docs

Excel Workbook

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