Computer assisted evaluation of gas sensors : theory and applications

Abstract: The application of a low cost computer as program control in a laboratory experimental situation is valuable for the evaluation of a complex measurement problem. The first step in a computer assisted evaluation is to design the experimental methods and construct the apparatus. The second step is to evaluate the results obtained by the use of the experimental system. The scientist does not need to take part himself in the experiment and has thus no possibility to influence the results of the investigation during this part of the investigation.  his is positive in the name of objectivity.This thesis contains a description of a computer system, the computer programs and measurement techniques applied to the evaluation of a solid state gas sensor. The sensor studied is a palladium-silicon dioxide-silicon structure with large sensitivity and selectivity for hydrogen in air. This is due to a "channel" open for hydrogen atoms only to reach the palladium-oxide interface, where they give rise to a voltage drop. Through the use of the computer assisted evaluation of the gas induced changes of the surface and interface potential it was possible to propose a model for the catalytic reactions between hydrogen and oxygen on the palladium surface. Three discrete modes of the short term behavior of the sensor were identified, and described by a physical model which incorporate a competion between hydrogen and oxygen for adsorption sites on the metal surface. This had probably not been possible without the use of computer assisted evaluation.It was shown that in porous palladium films also other species than hydrogen atoms reach the palladium-oxide interface. It was thus possible to detect other gases, like carbon monoxide, with a porous metal gate.The gas sensor was originally developed as a hydrogen sensor to be used in air. In the thesis it is shown that the non-porous palladium gate gas sensor is also very useful as an oxygen sensor in an oxygen free background. This application is interesting for the analysis of the oxygen content in e.g. blood or in an inert (food) storage atmosphere.