Analysis of changes in the current supplied to heat dissipation sensors

Abstract

In this study we assessed the effects of heater wattage on sap flux estimates from heat dissipation sensors. We used a total of eight trees ranging from 3-6 cm in diameter. Our calibration experiment was performed with a modified tree-cut approach, which allowed us to estimate gravimetric water use manually by weighing 20-L buckets every 15 min, while sap flux was monitored on each tree. Our results indicate that the average percent error for each wattage was: 0.15 W = 9%, 0.19 W = 1%, 0.2 W = 4% and 0.25 W = 13%, and changing the current supplied to the heaters does not significantly influence sap flux estimates, as long as the maximum differential voltage (ΔTmax value) is properly determined for each current adjustment period, and natural temperature gradients are corrected. Using the original parameters, sap flux density and sap flow had an average underestimation of 53%, which according to our analysis was correlated to tree diameter (R2=0.5, linear regression). The results of our experiment may allow researchers to supply different currents to heat dissipation sensors to increase sensitivity or reduce power consumption. The relationship observed between estimation error and tree diameter indicates that correcting by diameter is an alternative to generate species-specific parameters in heat dissipation sensors.