A Compact Optical Instrument with Artificial Neural Network for pH Determination Capel Cuevas, Sonia López Ruiz, Nuria Martínez Olmos, Antonio Cuéllar, Manuel P. Pegalajar Jiménez, María del Carmen Palma López, Alberto José Orbe Payá, Ignacio De Capitán Vallvey, Luis Fermín Portable instrument H coordinate HSV colour space pH sensor array Neural networks The aim of this work was the determination of pH with a sensor array-based optical portable instrument. This sensor array consists of eleven membranes with selective colour changes at different pH intervals. The method for the pH calculation is based on the implementation of artificial neural networks that use the responses of the membranes to generate a final pH value. A multi-objective algorithm was used to select the minimum number of sensing elements required to achieve an accurate pH determination from the neural network, and also to minimise the network size. This helps to minimise instrument and array development costs and save on microprocessor energy consumption. A set of artificial neural networks that fulfils these requirements is proposed using different combinations of the membranes in the sensor array, and is evaluated in terms of accuracy and reliability. In the end, the network including the response of the eleven membranes in the sensor was selected for validation in the instrument prototype because of its high accuracy. The performance of the instrument was evaluated by measuring the pH of a large set of real samples, showing that high precision can be obtained in the full range. 2013-10-21T10:45:14Z 2013-10-21T10:45:14Z 2012 info:eu-repo/semantics/article Capel-Cuevas, S.; et al. A Compact Optical Instrument with Artificial Neural Network for pH Determination. Sensors, 12(5): 6746-6763 (2012). [http://hdl.handle.net/10481/28497] 1424-8220 http://hdl.handle.net/10481/28497 10.3390/s120506746 eng http://creativecommons.org/licenses/by-nc-nd/3.0/ info:eu-repo/semantics/openAccess Creative Commons Attribution-NonCommercial-NoDerivs 3.0 License MDPI