Distributed chemical sensing

When a gas mixture is passed over a catalytic surface its composition will change due to the catalytic activity of the surface. Different molecules have different reaction rates and this fact can be used in combination with distributed chemical sensors to increase the discriminating capability of the sensors. in a measurement cell (palladium covered or non-covered) a row of identical Pd-MOSFET sensors was mounted along the flow direction. The catalytically active measurement cell changed the concentration of detected molecules (hydrogen or ethanol) considerably compared to the non-catalytic cell. It was observed that even catalytic combustion in the lid 1 mm above the sensor row influenced the sensor responses significantly. When comparing hydrogen and ethanol it was found that the two molecules were influenced to different degrees when passing the catalytic surfaces. Hydrogen was consumed at a much faster rate, which could tie seen when comparing the sensor responses along the row. A distributed sensor system thus shows an increased discriminating power. It was also found that chemical sensing was much more temperature dependent for ethanol than for hydrogen. (C) 1997 Elsevier Science S.A.