Indirect thermoelectric gas sensors

This introductory section will describe the various issues that are motivating research on direct thermoelectric gas sensors before presenting a brief introduction to thermoelectric power for the general reader. The principles of direct and indirect thermoelectric gas sensors are then outlined, while early research work is reviewed in the final subsection. 

Thermoelectric gas sensors can be divided more or less arbitrarily into direct and indirect thermoelectric gas sensors. Until recently, research has been mainly addressed to indirect gas sensors, and DTEGs have rarely been studied. Figure 7.1 explains the working principle for both types of thermoelectric gas sensor. 

Indirect thermoelectric gas sensors use the heat of an exothemfic reaction that stems from a combustible analyte. The temperature on a catalytically coated area of a (usually planar) substrate increases with the concentration of the analyte (Shin et al., 2003). The temperature difference between a catalytically inactive area on the substrate is usually measured either by thermocouples or by thermopiles. Therefore, this type of sensor is called an indirect thermoelectric gas sensor . Its measurement prmdple is similar to peUistor sensors (Willet, 2005). The thermoelectric material itself should not be catalytically active. The catalytically active coating of the thermoelectric... 

Principle of the set-up of (a) indirect, and (b) and (c) direct, thermoelectric gas sensors. The difference between (b) and (c) is the method of measuring the temperature difference AT. Reprinted from Rettig (2008) with permission from Shaker-Verlag. 

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