sensor for overvakning of sothalt in exhaust gases, especially from diesel engines

摘要

An insulating support body, for example an aluminum oxide ceramic, supports two electrodes spaced from each other by a small gap, for example 0.1 mm, which will have therebetween a high resistance. Upon collection of soot, the resistance between the electrodes across the gap will drop, which can be indicated by sensing current through the electrodes upon connection to a source of electrical energy. To remove soot upon termination of smoking, or soot contents in the gases, the electrodes are applied over, or embedded in a layer of essentially non-conducting catalyzing material which, in the presence of oxygen, catalyzes the oxidation of soot located in the gap between the electrodes to thereby remove the soot by oxidation and restore the resistance of the path between the electrodes and hence the sensitivity of the sensor for subsequent detection of accumulation of soot in the gap. Preferably, the non-conductive catalyzing material is a mixture of platinum, or a platinum metal, or a platinum metal alloy and a metal oxide which is compatible with, or identical to the ceramic base, for example aluminum oxide. The essentially electrically non-conductive layer can be applied by thick-film technology, and the electrodes also by thick-film technology thereover, or the electrodes may be in the form of fine platinum wires extending through the catalyzing electrically non-conductive layer. The sensing element can be held in a housing or socket, similar to a spark plug socket.