Development of a Sensor for Continuous and Accurate Monitoring of Air Flow for Open-System Whole Canopy Gas-Exchange Measurements

The research describes the development and set-up of a simple and accurate solid-state device for continuous monitoring of airflow forced into an open-flow gas-exchange chamber for whole-canopy transpiration and photosynthesis measurements. The ventilation system was formed by a centrifugal fan powered by an electric motor and a PVC pipe (0.193 m inner diameter). To damp airflow turbulence, 50 cm of the main pipe was filled with a bundle of smaller PVC pipes (3 cm inner diameter). The measurement principle of the sensor is the thermal balance of an electrically heated copper plate compared to an unheated one. Calibration of the sensor was performed by two independent methods: gas dilution (from a pure CO2 tank) and air velocity profiles measured by a hot-wire anemometer. Non-linear regressions fitted to the relationships between ΔT and both reference airflow measurements resulted in highly significant correlations with high r2 values (> 0.98).