The dendrometer is a low-cost system to measure the diurnal change in grape trunk diameter for varying sizes of grapevines. Measurements of daily fluctuations in trunk size can be used to determine the amount of water stress a plant is under, as well as predict veraison of the fruit.
Working with Dr. Alexander Levin, the base modular system is being developed to measure the radial trunk fluctuations for a grapevine with a diameter between 10 and 20 mm.
A BOM can be found here.
A 3048L linear potentiometer with a 12 mm stroke is used to measure the radial change in grapevine trunks over the course of 24 hours. The current precision is in increments of 12.5 microns. Based on previous research, Conesa et al. (2016) recorded a maximum daily trunk shrinkage (MDS) of up to 200 μm. While this research was conducted on significantly older grapes (11-year old drip-irrigated table grapes), the dendrometer project is starting with younger vines in greenhouses.
A feather M0 and Adalogger Featherwing + RTC are used to store data collected by a linear potentiometer. Every 5 minutes a sample is collected by the sensor. When three samples have been stored, the average is taken and then written to the micro SD card, so that there will be one data point every 15 minutes.
The frame was designed using Autodesk Fusion 360 and printed on Fusion3 F410 printer. Brass M2 Heat inserts provide hold for the screws and 30 mm long steel socket head screws are used to
Conesa, M. R., Torres, R., Domingo, R., Navarro, H., Soto, F., & Pérez-Pastor, A. (2016). Maximum daily trunk shrinkage and stem water potential reference equations for irrigation scheduling in table grapes. Elsevier. Retrieved July 22, 2019.