'Electronic nose'--new condition monitoring devices for environmental applications.

The responses of individual odour sensors combined into an array, where each sensor possesses slightly different response selectivity and sensitivity towards the sample odours, when combined by suitable mathematical methods, can provide information to discriminate between many sample odours (Pearce et al., 2002). Arrays of gas and odour sensors, made using different technologies, are finding their way into a variety of specialized applications (Persaud, 2001). Software techniques and material science are important aspects of the development of the systems. These devices have become known as ‘electronic noses’ and consist of three elements: a sensor array which is exposed to the volatiles; conversion of the sensor signals to a readable format; and software analysis of the data to produce characteristic outputs related to the odour encountered. The output from the sensor array may be interpreted via a variety of methods—such as pattern recognition algorithms, principal component analysis, discriminant function analysis, cluster analysis and artificial neural networks—to discriminate between samples. We describe three different environmental applications for such technology and illustrate how the problems were resolved.