IEEE TRANSACTIONS ON INSTRUMENTATION AND MEASUREMENT, VOL. 52, NO. 3, JUNE 2003 921 Tin Oxide Gas Sensing: Comparison Among Different Measurement Techniques for Gas Mixture Classification Ada Fort, Nicola Machetti, Santina Rocchi, M. Belén Serrano Santos, Luca Tondi, Nicola Ulivieri, Valerio Vignoli, and Giorgio Sberveglieri Abstract—In this paper, a study is presented aimed at the se- lection of the most appropriate measurement technique for wine classification. In particular, the problem of detecting typical wine aroma components in mixtures where ethanol is present is taken into account. The literature proposes different solutions in order to enhance metal-oxide sensor selectivity. An interesting approach concerns the application of different measurement techniques. In this work, three methods based on chemical transient, ac measure- ments, and temperature modulation have been investigated. Index Terms—Chemical transients, electronic nose, semicon- ductor gas sensor, temperature modulation. I. INTRODUCTION E LECTRONIC noses are complex systems for odor clas- sification whose structure is somewhat inspired to the mammalian olfactory system [1], [2]. The basic concept is the use of a sensor array made up of many sensing elements. The selectivity of each element is low, nevertheless the combination of the responses of different elements with different sensitivities has a characteristic pattern that can be seen as a “signature” of each different chemical mixture. The electronic nose structure comprises the sensor array, a conditioning and signal processing electronic system aiming at enhancing the array sensitivity (analog and digital processing) and finally a classifier that per- forms a comparison with a reference data-base. Obviously, the database cannot be exhaustive (due to noise, sensor response drifts, etc.), hence the comparison is performed by complex algorithms able to generalize (e.g., neural networks, fuzzy systems). Electronic noses allow to obtain a fast evaluation (from tens of seconds to few minutes) of a given odor mixture at a relatively low cost. Their analysis provide a global evaluation (the “signature”) of the odor composition. Traditional methods, gas chromatography (GC) and mass spectrometry (MS) [3], [4], on the other hand, provide a quantitative evaluation (identi- fication of each component) of the chemical composition of an odor. These methods are in general confined to the laboratory field and require a longer operating time (tens of minutes) and a greater expense (for the purchasing and the maintenance) in Manuscript received May 27, 2001; revised December 17, 2002. A. Fort, N. Machetti, S. Rocchi, L. Tondi, N. Ulivieri, and V. Vignoli are with the Department of Information Engineering, University of Siena, Siena, Italy. M. B. Serrano Santos is with the Department of Earth Sciences, University of Siena, Siena, Italy. G. Sberveglieri is with INFM and the University of Brescia, Brescia, Italy. Digital Object Identifier 10.1109/TIM.2003.814362 (a) (b) Fig. 1. Transient sensor responses normalized with respect to the sensor resistance in air . (a) TGS 2610. (b) SnO Pt-doped sensor from the University of Brescia. comparison to the electronic nose based one [5]. Considering wine-making applications (where conventional methods are widely used), electronic noses constitute a promising approach providing on-site operation, low cost, and real-time analysis. 0018-9456/03$17.00 © 2003 IEEE