Controlling nutrients in a hydroponic growing system

Sammanfattning: Hydroponics is a method for cultivating plants with their roots suspended in water. This means that the nutrients normally present in the soil have to be supplied artificially, in an appropriate amount. Electrical conductivity can be used to measure the nutrient concentration in a hydroponic solution. This thesis implements a small-scale model of an automated hydroponic farm. The nutrient concentrate is controlled automatically in a closed-loop system using conductivity measurements as input. Process control is realized through a pump delivering concentrated liquid nutrients. Trials are conducted by growing lettuce to evaluate the performance. Temperature variations are identified as a source of measurement errors. A compensation method is tested using a separate temperature sensor. Additional input signal filters, which may be used for improved results, are also discussed.