Using manual support adjustments, sweetpotatoes and peanuts have been grown consistently in experimental hydroponic systems designed for future long-term NASA space missions involving humans at the Tuskegee University NASA Center for Controlled Ecological Life Support Systems (CELSS) [I]. The hydroponic systems used for growing sweetpotatoes employ the Nutrient Film Technique (NFT) method. Such systems require accurate conitrol of nutrient solution volume, pH, temperature, and solution flow rate to improve nutrient and 02 delivery to the root system. The use of digital techniques in instrumentation are well established [2] - [4]. The National Instruments' LabVIEW is a programming system for data acquisition and control, data analysis, and data presentation using a Graphical Unit Interface (GUI) platform. LabVIEW offers an innovative programming technique in which software objects can be assembled graphically to form a virtual representation of the actual control system. With LabVIEW, block diagrams are assembled to represent the functioinalities expressed in the algorithms without worrying about the many syntactical
details of conventional programming. The objects in the block diagrams are connected by wires to pass data from one block to the next depending on the functionalities expressed in the algorithms - from simple arithmetic functions to complex data acquisition and complex analysis routines. The LabVIEW platform development is low cost, provides enhanced accuracy and added functionality, and saves time. An ulitrasonic sensor and pH sensor are interfaced to a PC through the National Instruments' plug-in data acquisition card. The LabVIEW provides functions to acquire and output data frorn the plug-in card. The purpose of this work is to present in detail algorithms for a virtual instrument (VI) that acquires data through a conventional plug-in data acquisition card to provide multifunction instrumentation for hydroponic crop production systems.
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