This project is an innovative, reusable device for measuring sap flow through trees.
The concept of using sap flow to measure the amount of water a plant in using goes back to the 1940s [1]. However, commercial solutions can be very expensive, and home-made versions tend to be difficult to make and easy to break.
Our task was to improve on a design started two years ago by the OSU OPEnS lab and OSU College of Agriculture (with sponsorship from the Washington Fruit Growers Associations). Previous teams had performed a lot of experimentation, but produced designs approaching a full system. Critical pieces of the project were missing and undocumented. We were tasked with creating an accurate, affordable sap flow meter within the year.
We wanted to address four issues issues: durability, cost, accuracy, and convenience.
Commercial sap flow measurement systems can cost up to $1000 per unit for measurement systems and data loggers. The cost for deploying our system is $365, with each additional sensor costing roughly $300 apiece.
To make our technology convenient, we focused on using easy to acquire parts and integrating smooth user interfaces. For instance, rather than requiring physical connection to check data gathered by a particular probe, we implemented LoRa wireless transmissions and a raspberry pi hosted central database so all data could be monitored and compared from a central location. We also created a web interface for said data.
Probe durability was an important part of our design. Previous iterations of the Sap Flow project found that even with an experienced assembler, 30% of thermocouples would be dysfunctional immediately upon creation. Once a working probe was inserted, it would be nearly impossible to remove without damage. To combat this, we switched from thermocouples to flexible PCBs protected by small steel tubes. This change reduced the failure rate, allowing us to reuse probes multiple times.
Unfortunately, we were unable to meet the accuracy requirements originally set out in our engineering requirements. This was mostly due to lack of long term testing, which was prevented by covid-19
For more details on the technical implementation and features our project, feel free to browse our website, linked below.
References:
[1] Schubert, A. “Der Wasserhaushalt Der Meso- Und Hygrophyten.” SpringerLink, Springer, Dordrecht, 1 Jan. 1940, link.springer.com/chapter/10.1007/978-3-642-94678-3_47
