Accuracy of Heat-Pulse Sensors for Determining Moisture of Capillary Mat Material Used to Support Plant Growth
Date of Award
Thesis - Open Access
Master of Science in Space Science
Dr. Mark Reynolds
Dr. Mehmet Sozen
Dr. John Mathis
Dr. Howard Levine
The accuracy and precision of Orbital Technologies (Orbitec, Madison, WI) Thermal and Moisture Acquisition System (TMAS) sensors were investigated for use in the WONDER space flight experiment. WONDER is studying the effect of multiple wetness level regimes and two different nutrient delivery systems (NDS) on plants grown in the microgravity of space. The following research concentrates on the porous tube NDS consisting solely of a capillary mat surrounding a bare porous tube used for water delivery. Sensors and plants will be attached to the capillary mat, which transports water by capillary action. The TMAS sensors, single probe heat-pulse moisture sensors, will measure the moisture level of the capillary mat as part of a moisture feedback irrigation control regime. Tests were done to determine temperature calibrations and the best mode of operation of the sensors in this unique medium. Then, repeatability, sensitivity, and verification investigations were completed as part of a moisture calibration. It was discovered that increasing the heating duration of the sensors enables better resolution of the different wetness level set-points. Furthermore, repeatability testing indicated a lack of precision in the sensors when used in this medium as readings on different days resulted in significantly different measurements. Relative water content (RWC) level differences of 15% were determined to be distinguishable for all sensors, while differences of 10% and even 5% were resolvable by some sensors. Also, when the moisture calibrations were subjected to verification testing there was found to be a dependence of the water content reading not only on the change in temperature of the probe, but also on its initial temperature. Inclusion of the initial temperature reduced the maximum mean arithmetic relative error of the calibration from 83.2 to 13.7%.
Scholarly Commons Citation
Wyssling, Marisa, "Accuracy of Heat-Pulse Sensors for Determining Moisture of Capillary Mat Material Used to Support Plant Growth" (2005). Master's Theses - Daytona Beach. 214.