Temperature compensation of pH Measurements Using a Fuzzy Inference System and Genetic Algorithms

Abstract

pH is a crucial variable in hydroponic crops that indicates the solution's acidity or alkalinity. It is necessary to control and adjust the pH in the nutrient solution of the crop since it affects the transference of nutrients to the root. The pH measurement compares the solution's potential with unknown [H+] with a known reference. At the same time, the function of the pH meter is to convert the voltage ratio between a reference and a sensing half-cell into pH values. In acidic or alkaline solutions, the voltage at the outer membrane sur-face changes proportionally to changes in [H+]. However, temperature affects the pH measurement, producing inaccurate measurements. The most complex sensors integrate Automatic Temperature Compensation (ATC) since they accurately adjust the electrode calibration for pH when the temperature changes. Nevertheless, ATC cannot correct for the pH/temperature effects of samples that are unknown. This research proposes a fuzzy interference system to compensate for the effects of temperature on pH measurement through a Mamdani interference system besides genetic algorithms to tune the vertices in the output arrays.