Project lead:

Brett Stoddard,


Dongjun Lee,

Jonathan Fookes,

Luke Goertzen,

Thermal Sap Flow


Thermal sap flow sensors were initially proposed in the paper "Untersuchungen über den Transpirationsstrom der Nadelhölzer und den Wasserbedarf von Fichte und Lärche (Studies on the transpiration flow of conifers and the water requirements of spruce and larch)" in 1940 by A. Schubert, et al. Since then, several key improvements have created a sensor that is semi-popular among researchers. However, their current high price point has limited adoption.

A good case study for the modern state of commercial thermal sap flow sensors are the ones produced by Dynamax. Their probe style sap flow sensor costs ~$350 for a single sensor with no data logger or voltage controller. That price can reach near $2000 with those included.

By using a few tricks in the design, we at the OPEnS Lab in collaboration with Friend of Trees hope to design a sap flow sensor that costs less an $50 to produce including labor (priced at $50/hour) that rivals the performance of current designs. I plan to do this by redesigning almost everything to incorporate modern surface mount manufacturing techniques and open sourced communication protocols.


  • Create SMD based Sap Flow design

  • Validate that design with in-situ testing

  • Further calibrate that design with lab trials

  • Produce sensors for Friends of Trees deployment Fall 2018


Current State

The newest prototype is installed in a cherry tree. It currently can record data for seven days continuously on the same battery with the new energy saving updates.


Sap flow, sap, thermal method, Grainier Method


  • Schubert, A. “Der Wasserhaushalt Der Meso- Und Hygrophyten.” SpringerLink, Springer, Dordrecht, 1 Jan. 1940,


How a thermal sap flow sensor works in theory.

How a thermal sap flow sensor works in theory.