Oxygen concentration measurement and control

Abstract

Method and apparatus are disclosed for measuring and controlling the concentration of oxygen in a gas. A sensor (10) is provided having a zirconium dioxide wall (12). One side of the wall is exposed to a reference gas having a known oxygen concentration while the other side is exposed to a gas having the unknown oxygen concentration. An electrical potential is developed at the sensor output, where the magnitude of the potential is dependent upon the relative oxygen concentrations on either side of the sensor wall and the temperature of the wall. The reference gas is selected such that variations in the electrical potential due to temperature changes are minimized over the expected range of temperatures to which the sensor will be subjected during the oxygen concentration measurements and over the range of oxygen concentrations which must be measured. The sensor temperature is measured by measuring the resistance of the sensor, which varies directly with temperature. An oscillator (28) provides an AC signal which is applied to the sensor (10) such that the AC signal is superimposed on the DC sensor output and has a magnitude dependent upon the resistance and therefore the temperature of the sensor. The AC and DC components are isolated from one another by two filters (32, 34) and separately utilized as temperature and oxygen concentration indications.

Dependencies are inferred from the claim text.