Servicio de Información Comunitario sobre Investigación y Desarrollo - CORDIS

Self diagnostic gas sensors for safety and the environment

The project concerns the development of self diagnostic gas sensors for safety and the environment. The sensors are novel multi-electrode devices which provide more detailed information about the gaseous environment in which they are placed, provide information on the validity of the information which is being generated, and give an indication if the sensors are failing through poisoning or some other ageing mechanism.

Planar thick film sensors have, until the present, had just two gold electrodes acting as contacts with the oxide ceramic so that its resistance can be measured. Now, differentially spaced electrodes have been introduced. The narrow gap electrode is employed to probe regions of the sensor close to the alumina substrate. In contrast the wide gap electrode pair is employed to monitor reactions occurring throughout the thickness of the sensor, allowing probing of reactions occurring at the outermost regions of the sensor. When gases react with the porous ceramic material a concentration gradient of target gases and reaction products is generally produced. Such a sensor can be calibrated empirically for a particular combination of gases. The electrode configurations were combined with three active semiconducting oxide materials which offer contrasting properties in terms of their gas detection response. These three different materials are suitable for detecting reducing gases and flammable gases, reducing toxic gases such as hydrogen sulphide, carbon monoxide and ammonia, and a material for detecting oxidizing gases such as ozone, chlorine, nitrogen dioxide and nitrous oxide.

In order to interrogate the sensors satisfactorily it was necessary to investigate simple electronic interface circuits, and the method adopted was an equi-potential approach wherein the voltage of each measuring electrode with respect to the common is the same irrespective of the resistance of that spacing. Signals derived from this interface circuit were employed in signal processing systems.


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