Huerta, R.; Mosqueiro, T.; Fonollosa, J.; Rulkov, N.; Rodriguez-Lujan, I. Chemometrics and intelligent laboratory systems Vol. 157, p. 169-176 DOI: 10.1016/j.chemolab.2016.07.004 Data de publicació: 2016-07-15 Article en revista
A method for online decorrelation of chemical sensor signals from the effects of environmental humidity and temperature variations is proposed. The goal is to improve the accuracy of electronic nose measurements for continuous monitoring by processing data from simultaneous readings of environmental humidity and temperature. The electronic nose setup built for this study included eight metal-oxide sensors, temperature and humidity sensors with a wireless communication link to external computer. This wireless electronic nose was used to monitor the air for two years in the residence of one of the authors and it collected data continuously during 537 days with a sampling rate of 1 sample per second. To estimate the effects of variations in air humidity and temperature on the chemical sensors' signals, we used a standard energy band model for an n-type metal-oxide (MOX) gas sensor. The main assumption of the model is that variations in sensor conductivity can be expressed as a nonlinear function of changes in the semiconductor energy bands in the presence of external humidity and temperature variations. Fitting this model to the collected data, we confirmed that the most statistically significant factors are humidity changes and correlated changes of temperature and humidity. This simple model achieves excellent accuracy with a coefficient of determination R2 close to 1. To show how the humidity–temperature correction model works for gas discrimination, we constructed a model for online discrimination among banana, wine and baseline response. This shows that pattern recognition algorithms improve performance and reliability by including the filtered signal of the chemical sensors.
Rodriguez-Lujan, I.; Fonollosa, J.; Vergara, A.; Homer, M.; Huerta, R. Chemometrics and intelligent laboratory systems Vol. 130, p. 123-134 DOI: 10.1016/j.chemolab.2013.10.012 Data de publicació: 2014 Article en revista
Weinvestigate optimal experiment selection to train a classifier on gas sensor arrays to get the maximal possible performance in a limited number of experiments. In gas sensing, while collecting data for a particular sensor array, one has to choose what gas and concentration level is going to be presented in the next experiment. It is an active decision by the operator selecting the experiments and training the classifiers. Can the algorithm be trained sooner rather than later? Can we minimize the costs of collecting the data in terms of the man-hour of the operator and the expenses of the experiment itself? Active control sampling provides a way to deal with the challenge of minimizing the calibration costs and is applicable to any situation where experimental selection is parameterized by an external control variable. Our results indicate that active sampling strategies can only improve a random selection of experiments over a wide range of concentration of gasses. However, random or uninformed selection is fairly close. Additionally, our active sampling methodology reveals that, when there is no prior knowledge about the range of concentrations to which the sensor will be exposed during real operation, sensor must be calibrated over the entire working range, not just high concentrations. In fact, our results show that it is especially important to include low concentrations in the calibration since the lack of these values would dramatically decrease the performance of the system.
Padilla, M.; Perera, A.; Montoliu, I.; Chaudry, A.; Persaud, K.C.; Marco, S. Chemometrics and intelligent laboratory systems Vol. 100, num. 1, p. 28-35 DOI: 10.1016/j.chemolab.2009.10.002 Data de publicació: 2010-01-15 Article en revista
Teodor, S.; Perera, A.; Pardo, A.; Hahn, S.; Marco, S.; Barsan, N.; Weimar, U. Chemometrics and intelligent laboratory systems Vol. 64, num. 2, p. 103-122 DOI: 10.1016/S0169-7439(02)00069-2 Data de publicació: 2002-11 Article en revista