Patent ID: 6566894
Filing Date: 2003-05-20
Classification: B01D,G01N,Y02A

Abstract:
A method for detecting oxidizable and/or reducible gases in the air for the purpose of controlling ventilation plants in buildings or motor vehicles and for the purpose of monitoring combustion processes or waste gas catalyst plants, comprisingemploying at least one electrically conductive and heated sensor (5.1; 7.2) furnished with contact electrodes (5.9; 5.10) and with a metallic sensor material; employing an electric evaluation circuit; passing an alternating current through the sensor (5.1; 7.2) wherein the alternating current either comprises at least two alternating currents of different frequency or is switched between at least two frequencies; evaluating a changing of the capacities between the sensor material and the contact electrodes (5.9; 5.10) depending on a presence of reducible gases and on a presence of a standard gas by the evaluation circuit as an indicator on the one hand; and evaluating a changing of the capacities within the mass of the sensor material (sensitive material) depending on a presence of oxidizable gases and on a presence of a standard gas as an indicator on the other hand; furnishing the sensor (5.1) as a component of an oscillating circuit (5.8; 7.1) for generating two different frequencies; periodically changing the oscillation of the oscillating circuit by switching frequency-determining components between at least two frequencies; individually evaluating and comparing the respective frequencies to the respective frequencies determined during operation of the sensor in standard air; employing frequency deviations as a measure for the concentration of groups of gas present; coordinating high frequencies always to reducible gases in the evaluation circuit and low frequencies always to oxidizable gases in the evaluation circuit; and determining the phase shifts, caused by the sensor-internal capacities, at individual frequencies; and decomposing the output signal into an imaginary part and into a real part, wherein the imaginary part and the real part represent a measure for the presence and kind of gases relative to values determined for standard air.