A Control System for Managing and Replenishing Nutrient Solution Based on Electrical Conductivity

An automated nutrient replenishment system has been developed in order to provide a constant electrical conductivity (EC) value for the nutrient solution over the period of plant growth. A single nutrient film technique (NFT) system developed by the Tuskegee University NASA Center was equipped with the EC control system for growth trials with sweetpotatoes. The system is completely controlled and monitored by a PC through the use of LabView instrumentation and data acquisition software. A submersible EC probe driven by an EC controller measures the EC of the nutrient solution reservoir. EC values are passed from the controller to the PC through analog outputs. If the EC is outside a given range, the PC sends a signal to one of two solenoid valves that allow concentrated stock solution or deionized water to enter the reservoir to either raise or lower the EC respectively. For this application the set point is 1200μS cm ^-1 , with a dead band from 1180 to 1220μS cm ^-1 . To aid in nutrient solution replenishments, an ultrasonic sensor was added in order to monitor and maintain constant nutrient solution levels in the reservoir. A similar growth channel (the experimental control) is set up for comparison using a manual method of nutrient solution replenishment. During the initial test run, the automated system held the EC within the designated range throughout the sweetpotato growth cycle.

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See papers presented at International Conference On Environmental Systems, July 1998, Danvers, MA, USA, Session: Regenerative Life Support Systems and Processes

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