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Herbaceous Sap Flow Sensor

Monitor sap movement in herbaceous plants

Miniature size heat pulse Sap Flow sensor ideal for smaller diameter stems and woody plants.



The Herbaceous Sap Flow Sensor uses the heat pulse velocity technique to assist with estimating plant water use, and is ideal for measurements in:


Plant Water flux

Estimate Plant transpiration

Irrigation scheduling

Sap Flow sensors are a simple, accurate and durable probe to be used in conjunction with Campbell Scientific Dataloggers.  


Although the sensor only requires only a Heater control interface and datalogger for proper use, 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 10mm x 1.27mm diameter

Temperature Sensors: 10K Precision Thermistor

Material: Epoxy and Delrin head, stainless steel needles

Cable length: 2m standard (additional cable available.)


The East 30 Sensors Herbaceous Sap Flow Sensor consists of three 10mm long stainless-steel needles spaced 6mm apart. One needle contains an Evanohm heater and the others contain a precision thermistor evenly placed at 5mm. The needles are inserted into holes drilled in the trunk of a tree with the heater placed between the thermistor. 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.


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.

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