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Bulk Moisture and Salinity SensorMeasurement and feedback control of nutrient solutions in plant root zones is critical to the development of healthy plants in both terrestrial and reduced-gravity environments. In addition to the water content, the amount of fertilizer in the nutrient solution is important to plant health. This typically requires a separate set of sensors to accomplish. A combination bulk moisture and salinity sensor has been designed, built, and tested with different nutrient solutions in several substrates. The substrates include glass beads, a clay-like substrate, and a nutrient-enriched substrate with the presence of plant roots. By measuring two key parameters, the sensor is able to monitor both the volumetric water content and salinity of the nutrient solution in bulk media. Many commercially available moisture sensors are point sensors, making localized measurements over a small volume at the point of insertion. Consequently, they are more prone to suffer from interferences with air bubbles, contact area of media, and root growth. This makes it difficult to get an accurate representation of true moisture content and distribution in the bulk media. Additionally, a network of point sensors is required, increasing the cabling, data acquisition, and calibration requirements. measure the dielectric properties of a material in the annular space of the vessel. Because the pore water in the media often has high salinity, a method to measure the media moisture content and salinity simultaneously was devised. Characterization of the frequency response for capacitance and conductance across the electrodes was completed for 2-mm glass bead media, 1- to 2-mm Turface (a clay like media), and 1- to 2-mm fertilized Turface with the presence of root mass. These measurements were then used to find empirical relationships among capacitance (C), the dissipation factor (D), the volumetric water content, and the pore water salinity.
Document ID
20130012688
Acquisition Source
Kennedy Space Center
Document Type
Other - NASA Tech Brief
External Source(s)
http://www.techbriefs.com/component/content/article/16115
Authors
Nurge, Mark (NASA Kennedy Space Center Cocoa Beach, FL, United States)
Monje, Oscar (Dynamac Corp. Cocoa Beach, FL, United States)
Prenger, Jessica (Dynamac Corp. Cocoa Beach, FL, United States)
Catechis, John (Dynamac Corp. Cocoa Beach, FL, United States)
Date Acquired
August 27, 2013
Publication Date
April 1, 2013
Publication Information
Publication: NASA Tech Briefs, April 2013
Subject Category
Man/System Technology And Life Support
Report/Patent Number
KSC-13039
Distribution Limits
Public
Copyright
Public Use Permitted.

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IDRelationTitle20130012640Collected WorksNASA Tech Briefs, April 2013
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