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Sap Flow 


Sensors are available in two and three needle configurations

High accuracy, low cost Sap Flow sensors for use in many applications.


The East 30 Sensors Sap Flow sensor uses the Heat Pulse Velocity technique to obtain specific and reliable results in all situations including:

Orchard and vineyard water use

Large-scale forest watershed monitoring


Species specific water requirements

Tree health monitoring

Irrigation scheduling

Sap Flow sensors are available in 2 and 3 needle designs to take the measurements you need.

Both styles use Heat Pulse Velocity to make a sap velocity measurement.

One needle contains an evanohm heater, and in the other needles contain 3 thermistors placed at 5mm, 17.5mm, and 30mm depths to accurately monitor sap flow across the entire depth of the sapwood.

Sap Flow sensors are a simple, accurate and durable probe to be used in conjunction with Campbell Scientific Dataloggers. For more information see Datalogger Compatibility or turnkey solutions if you have never worked with Campbell loggers before.


The Sap Flow sensor requires only a Heater control interface and datalogger for proper use, but the following are recommended to improve accuracy and installation ease:

·       Drilling Guide: for precise spacing of needles in the tree, a drilling guide is recommended for more accuracy in spacing as well as increased ease of installation.

·       Size 55 drill bit for best fitting installation

·       Mini hex chuck to hold drill bit securely for drilling.

·       Reflective insulation for temperature regulation

The Heater control interface, drilling guide, drill bits, mini hex chuck, and reflective insulation are available for purchase from East 30 Sensors. See Accessories for more info.




  • Head 45mm x 15mm;

  • Needles 35mm x 1.27mm diameter

Temperature Sensors:

  • 10K Precision Thermistor


  • Epoxy and Delrin head

  • Stainless steel needles

Cable length:

  • 2m standard (additional cable available.)


The East 30 Sensors Sap Flow Sensor consists of two or three (depending on model) 35mm long stainless-steel needles spaced 6mm apart. One needle contains an Evanohm heater and the others contain three precision thermistor sensors evenly spaced at 5mm, 17.5mm, and 30mm. The needles are inserted into holes drilled in the trunk of a tree with the heater placed below (upstream from) the thermistors in the two needle style or between in the three needle style. A current is applied to the heater for 8 seconds, at which time the temperature of the thermistors is monitored. The flowing sap carries the heat pulse to the sensors. The time taken for the pulse peak to reach the temperature sensors is monitored. This time is directly related to the sap flow velocity. The velocity is used, along with the sapwood area, to compute the transpiration rate of the tree. The three thermistors provide measurements of flow at three depths in the sapwood, from which the velocity profile can be deduced. In the three needle variation, the direction of sap flow can also be easily determined.


Cohen, Y., M. Fuchs, and G.C. Green 1981. Improvement of the heat pulse method for determining sap flow in trees. Plant, Cell and Environment 4:391-397

Green, S., et al. 2003. Theory and practical application of heat pulse to measure sap flow. Agronomy Journal 95: 1371-1379.

Pearsall, K.R., et al 2014. Evaluating the potential of a novel dual heat-pulse sensor to measure volumetric water use in grapevines under a range of flow conditions. Functional Plant Biology 41: 874-883.

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